Android d.ts Generator

A tool that generates TypeScript declaration files (.d.ts) from Jars/Aars

Because there are certain incompatibilities between Java and TypeScript, definitions MAY NOT always be completely accurate. They will however compile and provide auto complete feature inside a modern text editor supporting typings.

Quirks

Interfaces are represented by classes, this will allow you to extend them by using the new syntax, as well as show you all its members that need to be implemented
Classes from the package java.util.function don't have their typings generated, as function is a reserved keyword in TypeScript and JavaScript
Classes returning values of Type in the package java.util.function will return any instead
Classes using methods with parameters of Type in the package java.util.function will take any instead
Classes implementing java.util.Iterator, android.animation.TypeEvaluator, java.lang.Comparable do not implement those interfaces in the generated definitions for compatibility-related issues

Prerequisites

Gradle
Built gradle wrapper. Read more

Generate definitions following any of the approaches described below. Once you have run any of commands, you can find the generated typings in dts-generator/out directory.

Generate definitons for Android SDK

cd dts-generator
./gradlew jar
java -jar build/libs/dts-generator.jar -input %ANDROID_HOME%/platforms/android-<Platform Level (21/22/23/24)>/android.jar

Generate definitions for any Jar/Aar

cd dts-generator
./gradlew jar
java -jar build/libs/dts-generator.jar -input <Path to your Jar/Aar>

Pass multiple jars/aars to generator

cd dts-generator
./gradlew jar
java -jar build/libs/dts-generator.jar -input <jar1> <jar2> <jar3>

Another option is to pass the folder containing the jars you want to pass

cd dts-generator
./gradlew jar
java -jar build/libs/dts-generator.jar -input <jarFolder>

Note: Check the Makefile for sample usage

Test

In order to test the tool there are some predefined androuidx packages. We are running the tool and comparing the output with the expected output commited in the repo. To run the test:

make test-compare-output

Then check whether the make command will return an error comparing the files.

Note: If the libs folder content is changed, the expected output should also be changed

Generate definitions for .aar

Pass the aar as input as you would normally do

Complex typings generation

Generating the typings corresponding to the android and android-support jar files is a bit tricky operation, so here's a detailed explanation how to do it. There are different andoid support versions and they depend on main android classes it is a little bit complicated to generate those typings. One option is to generate a big d.ts file with all the libraries inside. The downside of this approach is that you have to generate a big file for every API level and if the android support version is changed all those d.ts files need to be regenerated. To avoid this there's some functionality in the tool for passing dependencies when generating typings. There are two type of dependencies that can be passed:

Super class jars - this is needed when the current jar has classes which are extending classes from another jar file, but we don't want to have all that jar files' typings in a single output file. To achieve this we can provide the super class jar with the super argument(which works the same way as input for multiple files). For instance if we want to generate typings for android.support.v4.view.ViewPager and we don't pass the super classes jar the generated typings won't extend any class as there's no information in the jar that contains the ViewPager. However this class extends android.view.ViewGroup class which is a part of the android jar file(any of the API levels). So if we pass one of the android.jar files as a super class jar file the generated typing will contain extends android.view.ViewGroup.
Input generics - When trying to get the type of a parameter which is a generic class we cannot really get the generic types of that class, so we cannot generate working typings. To fix this we are adding information about the generics of each package at the end of the file with comments starting with //Generics information:. So to fix this we need to provide a file with all the generic information for the packages the current jar relies on. You need to create a file and copy all the generic informations of the related packages and provide it in the input-generics argument. This will make all the generic classes referenced without passing types to pass any so that the ouput will be valid.

Adding all implements for generic types

There is an option all-generic-implements which is disabled by default which controls whether to add implements for all interfaces (if they are more than one) to generic type declarations. The problem is that in most of the cases one of those interfaces is actually an extend, so it should be manual reviewed and fixed after generation.

Finding package dependencies

If you want to generate typings of a package but you are not sure how you can get all the needed dependencies you can follow the steps bellow:

Open dts-generator/build.gradle file and locate dependencies part.

Add as a testCompileOnly dependency the one that you want to generate typings for:

dependencies {
    implementation 'org.apache.bcel:bcel:6.2'
    implementation 'commons-io:commons-io:2.6'
    implementation 'com.google.code.findbugs:findbugs:3.0.1'

    // add your dependency bellow
    testCompileOnly  "com.android.support:support-v4:27.0.1"
}

Open the dts-generator folder in your terminal
Run the following command:
```
./gradlew extractAllJars
```
The command above will get the needed jar files for your dependency and will output them in the dts-generator/jar-files folder (or you can optionaly pass another output folder -PjarsOutput=another-folder)
You can run the following command to check what are the dependencies between the packages:
```
./gradlew dependencies --configuration testCompileOnly
```
Run the dts-generator tool passing as input arguments the path to the output jars folder

Androidx specifics

To get all the jar files for androidx follow the steps above. You can find the jar files for androidx 1.0.0 in the current repository As androidx needs the base android jar file to create its typings you need to pass the android.jar file as a super parameter to the generator. To avoid having typings for every different API level you can reuse typings built with API level 17 for all API levels until 23. It's quite easy to test this:

Run the typings generator for androidx passing android-17/android.jar as a supper jar
Add /// <reference path="android-17.d.ts"/> at the top of the generated typings file where android-17.d.ts is the typings file of the android API level 17
Run tsc passing the generated typings file and there shouldn't be errors
Now start replacing the reference file with the files from other API level while the tsc execution completes with no error
If there's an error this means that you need to generate the android support typings with the same android API level super jar

By repeating the steps above we've found that:

Androidx 17 typings(built with supper jar from android API 17) can be reused until android API 22
Androidx 23 typings(built with supper jar from android API 23) can be reused until android API 25
Androidx 26 typings(built with supper jar from android API 26) can be reused for API 26 and 27

The corresponding typings files can be found in the tns-platform-declarations package. The repo's Makefile can be used as a reference for creating these typings files

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