Gsm voip gateway asterisk android jobs

I'm looking for an Android developer to work on my application. It will run on various platforms including Mobile device, Android TV OS, and Tablet. Existing Application will be shared with you . Key features of the application will include: - BLE Capture: Ensure the application can capture BLE data in real-time. - Data Uploading: Implement a mechanism for uploading collected data to the cloud. - Single Page Display: Design a single, easy-to-navigate page for the application. - Settings Page with Reports: Add a settings page where users can configure the app and view reports. - Devices Settings: Create a section for managing connected devices/settings. Key requirements: - Proven experience in developing Android apps, especially those involving BLE capture and ...

Looking for someone to develop a simple mobile app that will work on both iOS and android. That would mean utilizing one of those frameworks such as React Native or Cordova (or something else similar). The app will basically just allow the user to search for an order (done through a Rest API) and then select photos on the device and upload those to the selected order (also though a Rest API). Detailed Requirements: Setup screen where system URL and API key can be entered and then saved so subsequent uses of app doesn't require it to be reentered Ability to search and find order using order number, customer name, or company name Ability to select multiple photos and upload at once (although API call needs to be made for each file) Ability to take picture with camera right i...

I'm looking for an Android developer to create a simple news app for me. The key feature that I'd like to prioritize is an offline reading capability, which is essential for my users who may not have constant internet access. The news articles should be displayed in a list of headlines. This layout will allow users to quickly scan through the news and pick out articles of interest. The ideal candidate for this project would be a developer with experience in Android app development, particularly in working with APIs. Experience in designing user-friendly and intuitive interfaces would also be a plus.

...redesign with new idea. - Current website: , which is based on a PHP platform. - File delivery HTML based on Bootsrap template. Ideal skills for this project include: - Proficiency in website design with a strong portfolio showcasing similar projects - Excellent understanding of user experience and interface design - Experience in e-commerce website development, particularly with payment gateway integration - Knowledge of SEO best practices to ensure high visibility for our target audience. Proposal Submission: Important note: Before the project is handed over to you and discussed, Please submit an initial design concept or a sample idea that reflects your vision for the website along with your proposal. This will help us evaluate your understanding and approach towards th...

Android Developer - SMS Processing and Remote Management App We are looking for a talented Android developer to build a secure and feature-rich mobile application along with a Laravel-based admin panel for remote management. Responsibilities: Develop an Android application (minimum Android 8) with the following functionalities: Read incoming SMS and identify target keywords. Send identified keywords to a designated remote server. Receive and display SMS messages triggered from the admin panel. Implement a sync button to synchronize SMS data and send details to the remote server. Design and develop a secure admin panel using Laravel 10, MySQL 8, and PHP 8: User registration and management. Device registration with approval workflow. Device blocking functionali...

I am looking for an experienced freelancer to help me build a comprehensive website for selling furniture. The website should include the following features: - User-friendly design and navigation - Responsive design for mobile and desktop - E-commerce functionality with a secure payment gateway - Product catalog with high-quality images and detailed descriptions - User account management - SEO optimization - Integration with social media platforms - Analytics and reporting tools Please provide your portfolio, estimated timeline, and a detailed quote for the project. I am looking for someone who can deliver high-quality work and has a proven track record in developing e-commerce websites. Examples like : It should

I am looking for a skilled designer to help create an engaging Shopify website. I need the website to include a product catalog, a shopping cart, and an integrated payment gateway. I do not have a specific design in mind, and I welcome your creative suggestions. My preference, however, lies towards a minimalistic design with easy navigation. The ideal freelancer for this job would have: - Experience in designing Shopify websites. - A knack for minimalistic and intuitive design. - Accomplished skills in product catalog setup, shopping cart implementation, and payment gateway integration. - A creative mindset and the ability to incorporate my suggestions and ideas into the design. Your proposal will be more appealing to me if it includes links to previous Shopify websites yo...

Required a dot net developer. Speacialized in Microservices acrhitecture based solution. Dotnet Core, C#, SQL, Data transformation, API gateway, Auth based security.

...should provide tools for student registration, tracking student progress, and managing student profiles. - Lesson Scheduling: Users should be able to schedule lessons, view lesson details, and manage their availability. - Progress Tracking: The system must include features for tracking student progress, including test scores, attendance, and performance analysis. - Payment Gateway: Integration with a secure payment gateway to facilitate online transactions for course fees. Ideal Skills: - Strong PHP programming skills and expertise in building web applications - Proficiency in creating user-friendly and intuitive interfaces for various types of users - Experience in integrating payment gateways into web applications - Understanding of educational management systems or sim...

I am in need of an experienced app developer to create an Android E-commerce app. The primary function will be online shopping with a specific focus on an audit feature. Key Requirements: - Expertise in Android app development - Strong understanding of E-commerce app functionalities - Must be able to implement an Audit feature to ensure product verification. Your previous experience in building similar E-commerce platforms will be a huge advantage. Please provide a summary of your past projects when bidding.

I'm in need of an Android app developer to bring my idea to life.I have a ride hailing source code, i want someone who can install it in my playstore store console. this an urgent task apply if you can start immediately

...can create a clean and professional website that is also fully responsive and mobile-friendly. Ideal Skills & Experience: - Proficient in web development - Experienced in creating professional websites - Skilled in creating responsive and mobile-friendly designs Workflow: Customer fills out the booking form on our website with their details and preferences. Customer proceeds to the payment gateway (Razor pay) to complete the booking transaction. Upon successful payment, the booking details are stored in our database, and a unique booking ID is generated. Admin reviews new bookings via the admin dashboard and assigns cars and drivers based on availability. Customers receive confirmation of their booking along with trip details. Trips proceed as scheduled, with drivers provi...

...user privacy. - API Development & Integration: Develop new APIs and integrate with existing ones, for seamless communication between various components of the platform. - Data Processing & Analytics: Implement robust data processing and analytics functionalities to make informed decisions and gain insights from user interactions and other data sources. You will also be responsible for: - Payment Gateway Integration: Integrate payment gateways to facilitate transactions within the platform. - Social Media Integration: Implement connections with social media platforms to enable user sharing, login, or other interactions. - Maps and Location Services Integration: Incorporate maps and location services in the application where needed. Ideal candidates should be proficient i...

...search of an experienced professional mobile app developer to help in the creation of an educational app that will revolutionize the way users learn. Key functionalities: - Application of core educational tools and principles - User-friendly interface design Although the operating system compatibility is yet to be decided upon, the developer should ideally have experience with both iOS and Android. Showcase of cross-platform app building capabilities would be a significant advantage. A passion for creating educational tools and initiatives is paramount, and experience in that specific field would put you to the front of the line. Skills and Experiences: - Proven experience in mobile app development - Familiarity with common mobile interface designs - Strong understanding of e...

I am looking for a skilled PHP developer with experience in PHP frameworks, MySQL database, and E-commerce development to build a website. The developer should also have experience with Wordpress and int...and user-friendly online stores. - Proficiency in MySQL database is required. - The website will require integrating payment gateways, social media, and email marketing platforms. Hence, the developer should have experience in these areas. Ideal skills and experience: - PHP frameworks (Laravel, Symfony, CodeIgniter) - Wordpress - E-commerce site development - MySQL database management - Payment gateway integration - Social media integration - Email marketing integration If you have the expertise and skills required to execute this project effectively, please don't hesitate ...

...admin login section for authorization of completed job cards. We would like the system to export completed jobs to CSV file for automated invoice generation in Quickbooks Online. We will also require the system to import the customer database from Quickbooks in CSV format. Key Functionalities: - Creation and Editing of Jobs - Ability to use system on-site / remotely through the use of iOS or Android web browsing. Some - Ability to select a simple job status from a drop-down combo box eg. In-progress, waiting for collection, waiting on parts, not started, completed. - Ability to search by customer, PO number, job status, date, part on both active jobs and completed archived jobs in the past. - Ability to allow the upload of PDF files, pictures, notes etc for each job. - Abilit...

...suitable for adults on both Android and IOS platforms. Key Requirements: - **Game Type:** The ideal candidate should have a good grasp of designing puzzle games with a 3D interface. The game should be engaging and challenging, yet not overly complex. - **Target Audience:** The target demographic for this game is adults. I expect the freelancer to cater the game’s design, difficulty levels and overall gameplay to this age group. - **Graphical Quality:** The game should be designed with a 'cartoonish and simple' aesthetic. This means our target is a game that is visually pleasing but not overly complex or demanding on resources. Skills & Experience: - Experience in designing 3D games, particularly 3D puzzle games, would be highly beneficial. - Understandi...

I'm in need of an experienced app developer to create an e-commerce app for both iOS and Android platforms. The primary goal of this app is to support online purchases and transactions. Key features I'm looking for include: - A user-friendly interface for making purchases - Secure payment gateways for transactions - A robust product catalogue and search functionality - A system for tracking orders and managing accounts - Notifications for order alerts and promotional offers Experience in creating e-commerce apps is a must. Your expertise in both iOS and Android platforms is crucial, as the app needs to be developed for both. The app will need to be reliable, user-friendly, and secure to handle online transactions.

As I'm looking to establish a new SMM panel, I need a skilled developer who can integrate key features into the script. Here's an overview of what the project entails: - **Core Features**: Implement a User Management System, API Integration and Payment Gateway Integration. Given the sensitivity of the data involved, it's crucial that these features are robust, secure and user-friendly. Build a cross-functional SMM panel that generates and sells traffic for all social media platforms. - **Security**: Incorporate Two-Factor Authentication and an IP Whitelisting system. Additionally, the script should have an extensive Activity Log Monitoring mechanism. - **Performance**: Develop a script that prioritizes speed and responsiveness. This includes a Fast Loading Service, ...

I'm seeking a talented web developer to build an engaging e-commerce website for me. The website should be built on WordPress, or on framework like react aligning with the following specifications: - Includes standard e-commerce functionalities, such as a shopping cart, customer reviews, and payment gateway. - Integrates a unique 'grow a plant' game feature for users to interact with. The ideal freelance candidate for this project should have significant experience in e-commerce development, particularly on WordPress. The freelancer should also have a creative flair for integrating engaging features into a website. Previous experiences with gaming features will be an added advantage.

My project involves the development of an Android mobile app, primarily as a business tool with accounting capabilities. Key Features: - Splash Screen & Login with Auth Module: The app should have a splash screen and a login page that is modern and sleek in design. Your Skills: - Strong experience in Java for Android app development. - Knowledge in creating authentication systems. - Familiarity with inventory management and accounting concepts. I'm looking for a skilled developer who can bring these elements together in a user-friendly manner. The design should be modern and clean, reflecting the professional nature of the app's purpose.

...The interface should be intuitive and user-friendly, making it easy for users to navigate and interact with the application. - **Integration and Third-Party Services** I'd like to incorporate the following integrations: - Social media integration: The ability for users to share content and interact with the application through social media platforms. - Payment gateway integration: A reliable and secure payment gateway to facilitate transactions. - Email marketing services integration: Integration with email marketing services to streamline communication with users. Your expertise with Core Java, Java 8 features, J2EE, JDBC, servlets, MySQL, JSPs, HTML, Spring MVC, Spring Boot, ORM, MVC Architecture, and API Development will be essential. Additionally,...

...business. Key Requirements: - Product Management: The website should be able to support a catalog of 51-100 products. It should allow for easy addition, modification, and removal of products. - Shopping Cart: A seamless shopping cart feature is essential for a smooth customer experience. It should be user-friendly and support multiple purchases. - Payment Gateway: Integration of a secure and reliable payment gateway is a must. The gateway should support major credit cards and other common payment methods. Please note that the project is for the website setup only. The design aspect will be handled separately. Experience in e-commerce website development, specifically on the Shopify platform, is a significant advantage. A strong understanding of FMCG businesses an...

I'm in need of an experienced PHP developer, well-versed in Core PHP and Wordpress Development. The ideal candidate must be able to work on various projects with the following requ...websites. - Database Integration and Management: Proficiency in MySQL is a must. The developer will be responsible for managing and integrating databases effectively into our sites. - Payment Gateway Integration: The developer will have to implement payment gateways, ensuring a smooth and secure payment process for our users. Ideal Skills: - Proficiency in Core PHP and Wordpress Development - Strong understanding and experience with MySQL - Previous experience in User Authentication and Authorization - Previous experience in Database Integration and Management - Previous experience in Payment G...

I'm looking for an experienced app developer to create a comprehensive e-commerce application for both iOS and Android platforms. Key Features: - Implement a functional and secure shopping cart system - Develop user profiles with seamless registration and profile management - Integration of a reliable payment gateway for smooth transactions Ideal Skills and Experience: - Proficient in cross-platform app development - Proven experience in e-commerce app creation - Knowledge of implementing and securing payment gateways - UI/UX design skills to ensure user-friendly interface

I'm seeking a skilled developer to integrate the Razerpay payment gateway into my custom-built website. The project will include the following requirements: - Integration of Razerpay payment gateway: The developer should be experienced in integrating payment gateways and should have specific experience integrating Razerpay. - Multi-currency support: The payment gateway should be able to handle transactions in multiple currencies. This may require additional configurations on both the gateway and the website itself. Ideal Skills: - Proficient in web development - Experience with custom-built websites - Experience with Razerpay integration - Knowledge of multi-currency payment processing

I'm in need of a skilled mobile game app designer who can create a virtual workspace game for both iOS and Android platforms. The primary genre will be a Virtual Work Space, which is a unique concept. It's a mix of productivity tools and a game. Key Features: - The app should have audio sharing capabilities where users can share audio files with each other. - The app will also have a feature which creates a virtual lecture hall where users can attend virtual lectures. Ideal Skills: - Strong experience in mobile game app design, especially for iOS and Android platforms. - Understanding of virtual workspaces and productivity tools. - Previous experience with audio sharing and lecture hall features would be highly advantageous.

I'm in need of an E-commerce app for Android devices. It should be designed to support credit card payments exclusively. Key Features: - E-commerce Platform: The app should facilitate online sales through an intuitive and responsive interface. - Payment Integration: The app should provide seamless credit card transactions. - User Accounts: The app should offer user accounts with profile customizations and purchase history tracking. Requirements: - Proficiency in Android app development. - Previous experience with E-commerce platforms and payment gateways. - Ability to implement and manage user account systems. - A keen eye for UI/UX design and user experience optimization. Please only apply if you have a solid portfolio of similar projects.

Make an Android app which can be installed on customer phone(new/old) and if customer defaults EMI payments, I can lock customers' phone remotely.

I am in need of a React Native developer to create a digital HR face recognition app for attendance marking. Key Requirements: - The app should be compatible with Android devices. It will not be deployed to iOS. - The facial recognition data should be secured with standard encryption. - No integration with existing HR software is needed. The ideal candidate should have experience with: - React Native and building mobile apps. - Implementing facial recognition technology. - Ensuring data security through encryption. I am open to suggestions and ideas on how to enhance the app's performance and usability. Looking forward to your proposals.

I'm encountering a recurring issue where my Azan Android service stops every few hours, causing the prayer time notifications to cease. I need to restart mobile or reselect the Muezzin again then the service works few hours and then again dies. I need an expert in Android development to help me address this issue and enhance the stability of the service. service code I will provide, the freelancer needs to find the bug in the code and resubmit the file. Please include in your bid an overview of how you would approach this problem and your relevant experience. Regards

I am in need of an experienced Android developer with a demonstrable background in creating utility apps. The core features should include: - Synchronization across devices: The app should seamlessly synchronize data and tasks across various devices. - Offline usability: It's of utmost importance that this app retains full functionality even when offline. - User analytics: The ability to analyse user activity within the app will be a key feature to help modify and improve usability. The ideal candidate will have a strong understanding of Android development, and previous experience with device synchronization, offline usability, and user analytics. You must demonstrate your experience in these areas for your bid to be considered.

As an Android developer, I am seeking a professional with expertise in Android Studio using Java who can support me in executing key tasks for my app. The main areas of support needed are app functionality and bug fixing. Key Tasks: - App Functionality: Your role will involve implementing and refining specific functionalities within the app. This includes features like push notifications and user authentication. Ideally, you will have a strong understanding of Android development best practices and be able to translate user requirements into tangible features that enhance the app's overall usability and appeal. - Bug Fixing: Being able to troubleshoot and resolve any technical issues or bugs that may arise during the development process is crucial. Your ability ...

Integrate payment gateway. Payment gateway dont have suitable sdk for flutter. Flutter App.

*Project Title:* Developer Needed for Social Media App Development *Project Description:* We are seeking an experienced and talented developer to create a social media application for both iOS and Android platforms. The app will allow users to create profiles, describe their interests, post videos, and comment on others' posts. Our goal is to build a user-friendly platform that fosters engagement and community. *Key Features:* - *User Profiles:* Users can create and customize profiles, including personal information and interests. - *Video Posting:* Users can upload, share, and view videos. - *Commenting:* Users can comment on videos posted by others. - *Like and Share:* Users can like and share posts within the app

I'm looking for a skilled PHP developer with experience in CodeIgniter for...HTML5, and CSS3 - Knowledge of MySQL and other relational databases - Familiarity with RESTful APIs and Web Services - Ability to work with version control systems like Git The primary goal of the project is to create a robust, scalable, and user-friendly e-commerce platform. The platform should be able to handle a large number of products, facilitate smooth transactions, provide a secure payment gateway, and have a user-friendly interface. A key part of the role will be to ensure the system is built with scalability and maintainability in mind, to support future growth and modifications. If you have experience in CodeIgniter and e-commerce development, please reach out with your portfolio and relev...

...including MacOS and iPhone.*** I require a skilled Flutter developer with specific experience in OpenVPN, as well as iOS and Android app development. I have early built iOS project built with swift and I want you to recreate this iOS project to Flutter with 1:1 conversion. I will share the project if you have proven experience with flutter, iOS and Android. This app should also work properly on Android TVs also. Key Project Details: - Development for both iOS and Android platforms - Primary function: OpenVPN connectivity - Utilization of pre-existing iOS project for design Key Responsibilities: - Develop an OpenVPN application with Flutter for both iOS and Android - Ensure the app is functional and performs as expected - Utilize the existing iOS proj...

I'm looking for a skilled UX designer to create a social networking app for both iOS and Android. - The goal is to create a user-friendly, visually appealing interface that encourages engagement and social interaction. - The design should be fully customizable, allowing users to personalize their profiles to suit their preferences. Ideal candidates should have experience in UX design, particularly in the social networking space, and a strong understanding of mobile app design principles. Proficiency in tools like Sketch, Adobe XD, or Figma is a plus. Please provide relevant samples of your previous work in your proposal.

I need a dedicated Android developer to create an intuitive and secure membership application. The app is expected to include the following core features: - User Registration: A seamless and user-friendly registration process that captures necessary details. - Login: A secure login system that ensures data protection. - Profile Management: An easy-to-navigate profile section that allows users to update and manage their information. Additionally, the application must integrate a payment processing system. In this regard, the app should support credit card payments. Ideal skills and experience for this project include: - Proficiency in Android development - Expertise in UI/UX design and user flow - Prior experience in developing membership or payment applications - Demonst...

I'm looking for a skilled programmer to help me convert my invention into an app for iOS and Android devices. It is preferred that you're located here in SAN DIEGO, CA...however it's not absolute. Key requirements: - I'm open to the programming language, so your expertise in Python, Java, or C and C ++ would be beneficial in guiding the decision. - The main functions the app should possess are user authentication and data storage. I will require a Non Disclosure Agreement [NDA] to proceed with details of the invention. If you've got experience in app development [Coding] and can help me bring my invention to life on mobile devices, please reach out. Looking forward to working with you! Thanks, Mike

I need a proficient PHP developer to address an integration issue I'm experiencing with the Ccavenue payment gateway on my website. Key Tasks: - Resolve the integration issue occurring at a specific stage of the payment process. - Implement the necessary changes to ensure the payment gateway functions seamlessly. - Integrate a new control panel in the admin panel. Ideal Skills and Experience: - Strong command of PHP, particularly in relation to payment gateway integration. - Previous experience with Ccavenue payment gateway is highly preferred. - Proficiency in admin panel development. - Ability to troubleshoot and identify issues efficiently.

...including MacOS and iPhone.*** I require a skilled Flutter developer with specific experience in OpenVPN, as well as iOS and Android app development. I have early built iOS project built with swift and I want you to recreate this iOS project to Flutter with 1:1 conversion. I will share the project if you have proven experience with flutter, iOS and Android. This app should also work properly on Android TVs also. Key Project Details: - Development for both iOS and Android platforms - Primary function: OpenVPN connectivity - Utilization of pre-existing iOS project for design Key Responsibilities: - Develop an OpenVPN application with Flutter for both iOS and Android - Ensure the app is functional and performs as expected - Utilize the existing iOS proj...

I require an experienced PHP developer who can quickly resolve two broken links on my e-commerce website. The first issue is in the search line reset menu, while the second is between the cart and the payment gateway. Key Responsibilities: - Fixing two broken links in the e-commerce page - Ensuring the page stops looping - Ensuring the page retains user details between stages - Enabling users to progress to the payment page The fix needs to be completed in the next week. Ideal Candidate: - Proficient in PHP, particularly in e-commerce settings - Strong understanding of custom coding - Ability to work efficiently and meet deadlines - Experience in troubleshooting and resolving similar issues I have existing documentation and code comments available for the sections with issue...

Hi, We’re looking for a skilled female app developer to build a quick MVP and convert a physical card game into a mobile app game for both iOS and Android platforms. Quick note: I appreciate those who feel the need to start a chat and not so much those who have not bothered to read the brief before wanting to chat. I'll only start a chat if you have at least 2 to 4 links to card games you have published. Skills and experience required for this project: Experience converting physical card deck games into digital game experiences would be the ideal provider. The game brief overview: "Ello" is a two-player game played with a standard 52-card deck, where each player starts with 26 cards. The game assigns values to only four cards in the deck. In each turn...

Website Development for Education Purpose - I am looking for a developer to create a website for education purposes. - The website will primarily be used for uploading question papers in PDF format and providing a student login dashboard. - I prefer the website to be developed on WordPress. - The key functionalities I require are user registration and ...dashboard. _Conducting online quiz with ranking and candidate wise SWOT analysis. Ideal Skills and Experience: - Proficiency in WordPress development - Experience in creating user registration and login systems - Ability to implement content upload and download features - Knowledge of creating interactive dashboards - Familiarity with education-related websites and requirements Payment gateway and social media integration...

I am seeking a WordPress developer with experience in e-commerce website development. The project primarily involves customizing a theme for e-commerce functionality and developing plugins, particularly for product customization and payment gateway integration. Key Tasks: I need to build like Ideal Skills and Experience: - Proficiency in WordPress, including theme customization and plugin development - Experience in e-commerce web development - Knowledge of product customization and payment gateway integration - Strong problem-solving skills and ability to work independently If you have a solid understanding of WordPress and e-commerce, and you're able to work on the specified tasks, I would like to hear from you.

...user-friendly and efficient, streamlining the grocery shopping and delivery process. - Integration with PayPal and a European payment gateway is necessary. - The inventory management system must be integrated with WooCommerce. Support and Deployment: - Your role will extend beyond development; you'll be required to provide detailed support to my in-house tech team for deployment and maintenance. - The final product should be fully functional and ready for use. Skills and Experience: - Proficiency in full-stack development, with experience in creating and deploying similar applications. - A strong understanding of e-commerce, inventory management, and payment gateway integration. - Experience with WooCommerce is highly preferred. - Knowledge of European language tran...

I'm looking for a skilled app developer with expertise in both iOS and Android platforms. The primary function of the app is car service booking. It should have a clean, intuitive interface and be secure to ensure user trust. Ideal Skills and Experience: - Expertise in developing apps for both iOS and Android - Experience in developing service booking apps - Knowledge of secure app development - Strong UI/UX skills Features to Include: - Users should be able to book and pay for services - The app should store previous service records for easy rebooking - Should have a system to compare prices from different service providers. Your proposal should include a timeline and cost estimates for the project.

...the platform onto various social media channels. Qualifications: Proven experience as a PHP Laravel Developer, with a strong portfolio of completed projects. Proficiency in PHP, Laravel, MySQL, HTML, CSS, JavaScript, and related technologies. Strong understanding and experience in user management systems, role and permission setups, and user profile management. Previous experience with payment gateway integration. Prior work with social media sharing feature implementations. Ability to dedicate full-time to the project is crucial. Familiarity with version control systems (e.g., Git). Strong problem-solving skills and attention to detail. Ability to work independently and as part of a team. Excellent communication and collaboration skills. Preferred Skills: Experience with front...

I require development of a website and apps for iOS and Android platforms, with matching features and functionalities for a mobile data plan service. This project necessitates: - The creation of user accounts and profile management system. - Capabilities for subscribing to various mobile data plans - Seamless synchronization between website and mobile apps Ideal candidates should have prior experience in eCommerce site design and mobile app development, and be fluent in creating user-friendly interfaces. A grasp on data security measures for user account management and subscription systems is also essential. cellForRowAtIndexPath.