Run task before compilation using Android Gradle plugin

Question

I have a very simple build.gradle file with the following content:

buildscript {
    repositories {
        mavenCentral()
    }

    dependencies {
        classpath 'com.android.tools.build:gradle:0.4.1'
    }
}

apply plugin: 'android'

android {
    buildToolsVersion "17.0.0"
    compileSdkVersion 17

    sourceSets {
        main {
            manifest.srcFile 'AndroidManifest.xml'
            res.srcDirs = ['res']
            assets.srcDirs = ['assets']
        }
    }
}

task generateSources {
    doFirst {
        def script = "python GenerateSources.py".execute()
        script.in.eachLine {line -> println line}
        script.err.eachLine {line -> println "ERROR: " + line}
        script.waitFor()
    }
}

What I want is to run generateSources task before java compilation is started. I found several solutions how to do that, like compileJava.dependsOn("generateSources"), but unfortunately they give an error:

A problem occurred evaluating root project 'Android'.
> Could not find property 'compileJava' on root project 'Android'.

I don't know Gradle and can't understand what's wrong with this code. So I would like to know how I can fix this error.

Solution 1

The proper way to run a task before Java compilation on Android is to make a compilation task for each variant depend on your task.

afterEvaluate {
  android.applicationVariants.all { variant ->
    variant.javaCompiler.dependsOn(generateSources)
  }
}

Solution 2

Apparently, the android plugin doesn't add a compileJava task (like the java plugin would). You can check which tasks are available with gradle tasks --all, and pick the right one for your (otherwise correct) dependency declaration.

EDIT:

Apparently, the android plugin defers creation of tasks in such a way that they can't be accessed eagerly as usual. One way to overcome this problem is to defer access until the end of the configuration phase:

gradle.projectsEvaluated {
    compileJava.dependsOn(generateSources)
}

Chances are that there is a more idiomatic way to solve your use case, but quickly browsing the Android plugin docs I couldn't find one.

Solution 3

You can see task execution in terminal running task for example gradle assemble. Try this one, it is started practically before anything.

android {
    ...
    gradle.projectsEvaluated {
         preBuild.dependsOn(generateSources)
    }
    ...
}

Edit, this may not work in Android Studio, as the Android Gradle DSL does not have a projectsEvaluated method.

Solution 4

Try this:

buildscript {
    repositories {
        mavenCentral()
    }

    dependencies {
        classpath 'com.android.tools.build:gradle:0.4.1'
    }
}

apply plugin: 'android'

android {
    buildToolsVersion "17.0.0"
    compileSdkVersion 17

    sourceSets {
        main {
            manifest.srcFile 'AndroidManifest.xml'
            res.srcDirs = ['res']
            assets.srcDirs = ['assets']
        }
    }
}

task generateSources {
    def script = "python GenerateSources.py".execute()
    script.in.eachLine {line -> println line}
    script.err.eachLine {line -> println "ERROR: " + line}
    script.waitFor()
}

project.afterEvaluate {
    preBuild.dependsOn generateSources
}

clean.dependsOn generateSources
clean.mustRunAfter generateSources

The last two lines are optional - they will invoke the "generateSources" task when executing a gradle clean

View more solutions

Comments

[Peter Niederwieser]

What is it that doesn't work, and what's the exact error message?

[Michael]

The problem is the same as before: Could not find property 'compileDebug' on root project 'Android'.

[Peter Niederwieser]

And you verified that compileDebug exists? Does gradle compileDebug work? Did you add the dependency declaration at the bottom of the build script? You can also try tasks.compileDebug, but it shouldn't make a difference.

[Michael]

gradle compileDebug works fine. At the bottom of the file I added compileDebug.dependsOn("generateSources"). When I write tasks.compileDebug instead of compileDebug gradle gives me an error Could not find property 'compileDebug' on task set.

[Peter Niederwieser]

Browsing the Android plugin docs, I realized that it works quite differently from most other plugins. Does gradle.projectsEvaluated { tasks.compileDebug.dependsOn(generateSources) } work? Probably there's a more idiomatic way though.

[Michael]

Yeah, seems it works! Could you please add it to the answer and explain what it means?

[slott]

Awesome - have been at this for days now not understanding why the usual dependsOn failed for the pre defined tasks. Now I can finally add a dependency to the connectedCheck.

[Dhrupal]

Hello Peter Niederwieser, it giving me below error. Could not find property 'compileJava' on com.android.build.gradle.AppExtension_Decorated@44b35022.

[ento]

The task name seems to have changed to compileDebugJava.

[treesAreEverywhere]

I've got a task that needs to run before the Android build. Task copies a jar file into the libs directory. Somehow, this happends too late for the Android build. My android build always fails the first time after a clean. Then the second time it works ( since the jar file is there then). How do run the task that copies the jar file soon enough?

[treesAreEverywhere]

@PeterNiederwieser any chance you can update your answer? It's seems to be quite out of date. (Sorry if this sounds a bit rude, it's not meant that way)

[Peter Niederwieser]

Why is it out of date?

[Greg Ennis]

Well, your answer still says "compileJava.dependsOn(...)" which doesnt work, as discussed in comments.

[IgorGanapolsky]

Where are you calling your custom task here?

[Michael]

generateSources is the custom task. And javaCompiler tasks becomes dependent on generateSources.

[Martin Zeitler]

./gradlew tasks --all in the project directory also shows the task's description.

[IgorGanapolsky]

What? I get an error: Could not find property 'preBuild' on root project

[IgorGanapolsky]

I get an error: Could not find property 'android' on root project

[IgorGanapolsky]

I get an error: Could not find property 'preBuild' on project ':app'

[Michael]

You have to apply the Android plugin before this code.

[Henadzi Rabkin]

So, probably it doesn't exists now on newer versions of Gradle

[IgorGanapolsky]

Did it ever exist in Android Studio? Or were you generally speaking about Gradle...

[Henadzi Rabkin]

It was used in one of my projects Igor

[Merk]

@IgorGanapolsky just put prebuild.dependsOn('someTask') within the android { } block, works like a charm. No need to invoke projectsEvaluated.

[Compaq LE2202x]

@Michael how do you do that? I'm using Android Studio

[Michael]

You just have to put this code into your build.gradle file.

[Compaq LE2202x]

@Michael How do I do this for multiple tasks?

[Michael]

You can call variant.javaCompiler.dependsOn(taskName) for every task. Another approach is to have a chain of task and call variant.javaCompiler.dependsOn(taskName) for the root one.

[ottago]

This is bad since it will run for every invocation. Including things like clean which probably isn't what you want. Depending on what it does it could trigger uptodate checks to do more things.

[Shubham AgaRwal]

Any suggestion who can get build type related info in Gradle task 'generateSources'

[Khongor Bayarsaikhan]

variant.javaCompiler is now obsolete, you should use variant.javaCompileProvider.get()

[lasec0203]

tsk...tsk..spent hours struggling with getting a task to run because I was putting related code ouside of the android {} block

[Henadzi Rabkin]

@lasec0203 thanks for pointing this out. I have made an appropriate edit,