Use Lambda expressions and Butterknife

Question

I tried to use Lambda expressions in my code and I got this error : lambda expressions are not supported at this language level

I just search for it on SO and found a solution adding this to gradle file :

compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }

defaultConfig {
        ...
        jackOptions {
            enabled true
        }
    }

Then I got a new error : Error:Could not get unknown property 'classpath' for task ':app:transformJackWithJackForDebug' of type com.android.build.gradle.internal.pipeline.TransformTask.

Searched on SO again and found this is because I can't use jack and apt at the same time... so I remove apt deleting those lines :

apply plugin: 'com.neenbedankt.android-apt'

dependencies {
        ...
        classpath 'com.neenbedankt.gradle.plugins:android-apt:1.8'
        ...
    }

And got a new error because ButterKnife needs apt...

So how use Lambda and Butterknife in the same project ?

Answer 1

You should use annotation processor for Butter-knife library in the build.gradle

 compile 'com.jakewharton:butterknife:8.4.0'
 annotationProcessor 'com.jakewharton:butterknife-compiler:8.4.0'

Full Gradle Looks like:

buildscript {
repositories {
   ....
}

dependencies {
    classpath 'com.neenbedankt.gradle.plugins:android-apt:1.8'
    classpath 'me.tatarka:gradle-retrolambda:3.4.0'
   .....
}}
apply plugin: 'me.tatarka.retrolambda'
......

android{
.....
 compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}

repositories {
}
dependencies {
    ..........
    compile 'com.jakewharton:butterknife:8.4.0'
    annotationProcessor 'com.jakewharton:butterknife-compiler:8.4.0'
 }
}

NOTE: Don't use jackOption = Enabled