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2016/8/24 App Inventor Extensions App Inventor Extensions App Inventor extensions Initial Release 1.0 (part of MIT App Inventor Release nb149) DRAFT: September 27, 2015 sample extensions are at: http://appinventor.mit.edu/extensions/ source code for sample extensions at: http://appinventor.mit.edu/extensions forum for feedback and comments: Extensions section of the appinventor forum Please help us test and provide your feedback. The extensions feature is still under development, and the internal formats are not yet stable. If you build extensions, be aware that you will probably need to rebuild them when the system changes. This applies not only the the extensions themselves, but to the projects that import them. For now, use this document to experiment with building extensions for your own use. If you publish your extensions for others to import into their own projects, be sure to warn people that your extensions may go of date and will need to be updated. Note: App Inventor extensions are supported only on Android devices running API Level 8 (Android system 2.2 Froyo) and above. This applies to creating extensions, building projects that import extensions, and running packaged APKs of projects that use extensions. 1. Overview of App Inventor extension components 2. Testing the current prototype 3. How to use extension components 3.1 Importing extension components 3.2 Some sample extensions to try 3.3 Building projects with extension components 3.4 Deleting extension components 3.5 Sharing projects that use extension components 3.6 Extension component repositories 3.6 Naming extension components 3.7 Updating projects that use extensions 4. How to create extension components 4.1 Practice building a simple component 4.2 Create your extension as an ordinary component and test it 4.2.1 Restrictions on extension components 4.2.2 Requesting permissions for the extensions you define 4.2.3 Using external libraries 4.3 Choose a package name for your extension 4.3.1 Change your extension to have the desired package name 4.4 Create the aix file for your new component 4.5 Sharing your extension Acknowledgements Appendix A: Temporary instructions for obtaining the source code 1. Overview of App Inventor extension components App Inventor apps are built using components. Components let the apps use the builtin features of the mobile device (like Camera or LocationSensor) or services on the Web (like Twitter or FusionTables). App Inventor includes a large collection of components, and the App Inventor development team adds new capabilities to the system by implementing new components. https://docs.google.com/document/d/1orlYWGlHOY0hmAC0zjadQ4DET2K8U34C8hv5zmuxZLU/pub#h.5z6xqsl8lmwf 1/14

2016/8/24 App Inventor Extensions There have been many requests to include additional features in App Inventor. Some of these are specialpurpose features that would have only a few users, where it would be undesirable to include these in the core system for everyone. Other features might be good additions to the core system, but the App Inventor development team’s effort has gone to other priorities. Anyone can use the App Inventor free and open source code to implement their own components, but until now the only way to make these available to others has been to include them in private versions of App Inventor that are hosted and managed individually. App Inventor Extensions lets anyone create Extension Components. Extension components can be used in building projects, just like other components. The difference is that extension components can be distributed on the Web and loaded into App Inventor dynamically: they do not have to be built into the App Inventor system, and they can be imported into projects as needed. With extensions, the range of App Inventor apps can be virtually unlimited. One use of extensions, for example, is for educators and educational software developers to provide extension components tailored to specific lessons and activities that students can use in building apps. Examples might be simulations or data analysis tools. Those apps might be unfeasible to create directly with the builtin App Inventor blocks, either because of processing speed or programming complexity. But those same apps might be readily programmable in the App Inventor framework, using extension components that perform the necessary processing. Anyone can create extension components. This requires gaining familiarity with the App Inventor source code (located on Github) and programming the extension in Java. Extension components are packaged as aix files. Once you create an extension component, anyone can use it in their App Inventor projects. Extension component aix files can be housed anywhere on the Web. The aix files need not be stored at MIT or any other particular place, although MIT hosts a repository where people can make aix files available for sharing and public use. Note: One limitation of the current extension component implementation is that it creates nonvisible components only (i.e., components that do not show on the designer screen). MIT plans to remove this restriction in future versions of the extension component system. 2. Testing the current prototype Please send your comments and reports on you experiences with the test instance, by reporting them in the App Inventor Support forum under the extensions category. Caution: Do not transfer projects between the current testing instance and main MIT App Inventor. If a project uses extensions, it cannot run on the main MIT App Inventor system. You can take an ordinary project and upload it to the test system and add an extension, but the result cannot be exported back into the main MIT App Inventor. 3. How to use extension components You use an App Inventor extension component just as you would use an ordinary builtin component, except that you’ll first need to import the extension into your project. 3.1 Importing extension components Before you can import an extension component, you must have a project open. Start a new project, or open an existing one. To import an extension, look in the components palette at the left of the screen under Extensions and click the “Import extension” link as in the figure below. This will bring up a window that lets you specify an extension to import. Extensions are defined by aix files. You can import an extension from an aix file on your computer or you can specify a URL to import from the Web. https://docs.google.com/document/d/1orlYWGlHOY0hmAC0zjadQ4DET2K8U34C8hv5zmuxZLU/pub#h.5z6xqsl8lmwf 2/14

2016/8/24 App Inventor Extensions When you import an extension, App Inventor will give you the opportunity to rename it, as shown in the figure. Figure 1: Importing an extension https://docs.google.com/document/d/1orlYWGlHOY0hmAC0zjadQ4DET2K8U34C8hv5zmuxZLU/pub#h.5z6xqsl8lmwf 3/14

2016/8/24 App Inventor Extensions Figure 2: Renaming an extension when you import it. You’ll generally want to keep the default name. See the section below on naming for cases where you might want to choose a different name. Once you import an extension, it will appear in the components palette under the extensions category as shown in the figure below. After importing an extension, make sure to restart the companion app, else an error may occur. https://docs.google.com/document/d/1orlYWGlHOY0hmAC0zjadQ4DET2K8U34C8hv5zmuxZLU/pub#h.5z6xqsl8lmwf 4/14

2016/8/24 App Inventor Extensions Figure 3: An imported extension shown in components palette 3.2 Some sample extensions to try Here are some sample extension components to experiment with. You can find these in the MIT App Inventor Extensions repository at http://appinventor.mit.edu/extensions/. MIT will be adding more examples to this collection, and would like to evolve it into a site for people to share extensions. You can import the extensions using the URL indicated, or you can download the aix files to your local computer and import the files from there. ● VectorArithmetic created by Ethan Hon Takes in two vectors and can add them to return a result vector. https://drive.google.com/uc? export=download&id=0B22N7pfciq0CSHlFQVBCRk5OYlB3U3FDWFNlNDhvOVp5bDM4 ● ImageProcessor created by Justus Raju ImageProcessor can do a weighted combine of two images, return the greyscale of an image. http://appinventor.mit.edu/extensions/data/extensions/ai.cdk.justus.ImageProcessor.aix Here is a clean project that demos the use of the component. You can import this aia directly too. http://appinventor.mit.edu/extensions/data/demo/ImageProcessorDemo.aia ● SoundAnalysis created by Mouhamadou Oumar Sall Multimedia component that analyzes the pitch of a sound through the microphone and returns it. It can be used as an input to different situations, for instance to control some components with a specific sound whistle(pitch > 500Hz) or clap(pitch > 2000Hz). https://drive.google.com/uc? export=download&id=0B22N7pfciq0CUTZONWpKZUw2YXJlWHBMcERuaUliZWREdU5R ● ScaleDetector created by Hal Abelson This component add a pinch detector capability to a Canvas. For an explanation, see Using App Inventor extensions to implement multitouch. 3.3 Building projects with extension components https://docs.google.com/document/d/1orlYWGlHOY0hmAC0zjadQ4DET2K8U34C8hv5zmuxZLU/pub#h.5z6xqsl8lmwf 5/14

2016/8/24 App Inventor Extensions Once you have imported an extension component into a project, it will appear in the component palette under the Extensions section. You use the extension component just like any other component by dragging it from the palette to the designer screen, where it will appear under the designer screen as an nonvisible component. (Currently, all extension components are nonvisible components.) You’ll also see it in the Blocks Editor, together with blocks for its methods, properties and events. The figures below illustrate how an imported ImageProcessor extension would appear the Blocks Editor. Figure 4: Blocks for an imported ImageProcessor component 3.4 Deleting extension components To delete an extension from the project, click the X beside the extension. This will remove all uses of the extension and its blocks from the the project and you will not see it in Extensions palette panel anymore. https://docs.google.com/document/d/1orlYWGlHOY0hmAC0zjadQ4DET2K8U34C8hv5zmuxZLU/pub#h.5z6xqsl8lmwf 6/14

2016/8/24 App Inventor Extensions Figure 5: Click the X to delete an imported extension. 3.5 Sharing projects that use extension components You export and import projects that use extension components just like other App Inventor projects, as aia files. You need not do anything different in publishing the project than in publishing other App Inventor projects. If someone imports a project (aia file) that uses an extension, they do not have to import the extension (aix file) separately: When they open the project, the extension will appear in the components palette (under Extensions) together with the project’s other components. 3.6 Extension component repositories Extensions can be downloaded from any URL (provided you have access to it). Anyone who creates extensions can make the aix files available however they choose. It might also be convenient to create collections of extensions, called extension component repositories for private or shared use. For instance, an educator might create a repository of extension components for use in a course. The MIT AppInventor project has created a public repository for general use, to encourage people to create and share extensions. The repository is located at http://appinventor.mit.edu/extensions. 3.6 Naming extension components Extensions are created by different people working independently. So it’s likely that different extensions might have the same name. For example, there might be two different extensions called ImageProcessor, and you’d like to import them both. There’s no problem using the two extensions if you use them in different projects (other than that you might get confused). But you can’t import two extension with the same name into a single project. When you import and extension to a project, App Inventor will give you the opportunity to rename it, as shown in Figure 2. This will let you keep the extension names unique and also (should you prefer) choose names for the extensions that are more convenient for you than the original names. https://docs.google.com/document/d/1orlYWGlHOY0hmAC0zjadQ4DET2K8U34C8hv5zmuxZLU/pub#h.5z6xqsl8lmwf 7/14

2016/8/24 App Inventor Extensions (warning when you give the extension a name that already exists in the project) ` If you are developing extensions (not just using them) you can choose extension package names help minimize name conflicts. See the section on packages below. 3.7 Updating projects that use extensions We have not addressed the issue of what happens when extensions are updated and how people using the extension can be notified about this. There are two scenarios to consider: 1. The extension developer creates a new version of the extension, but the old version still works. 2. The App Inventor system is updated so that the extension no longer works. In either case, people importing the extension will need to look to extension developer to provide information about updating projects that import the extension Warning: The extensions system is still experimental and the internal format of extensions is changing. If you create a project (aia file) that imports an extension, it is possible that the extension (and the project) will stop working when the extensions system in upgraded. You’ll have to rely on the extension developer to provide an updated extension. 4. How to create extension components NOTE: As of 06/19/2016 Extensions must *not* be built in the com.google.appinventor.components.runtime package. You should use a different package name. See section 4.3.1 for more information. Extension components are created by programming in Java. The Java code can be original code that you write, and it can also include Java libraries (jar files) from other sources. You can create extension components for private use, or you can share them by sending people the aix files or making the files available on the Web. The process of creating an extension component is essentially the same as what people go through in creating an ordinary App Inventor components, both for MIT App Inventor or for local versions built using the App Inventor free and open source code. The difference is that the only way to make an ordinary component available to other people is to host your own App Inventor instance, whereas with an extension component, you can publish the aix files so that anyone can import it into any version of App Inventor. Building an extension component is no more difficult than building an ordinary component but then again, it’s no easier. If you’ve never created a component before, you should start by reading the these guides: ● How to Build App Inventor from the MIT sources This shows how to get the MIT App Inventor sources and how to use them to create a local App Inventor instance on your own computer for personal use Note: Please see Appendix A: Temporary instructions for obtaining the source code. This shows how to get the source for the extensions version of App Inventor, during this period when we are still testing. ● How to Add a Component https://docs.google.com/document/d/1orlYWGlHOY0hmAC0zjadQ4DET2K8U34C8hv5zmuxZLU/pub#h.5z6xqsl8lmwf 8/14

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