Android Studio - no debuggable applications

Just click the "Bug" icon and you will be good to go.

I had the same problem and that did the trick. hope it helps someone.

You also should have Tools->Android->Enable ADB Integration active.

The solution is to turn on debuggable flag (debuggable true) in application's gradle file:

apply plugin: 'com.android.application'

android {
    compileSdkVersion 19
    buildToolsVersion "20.0.0"

    defaultConfig {
        applicationId "org.example"
        minSdkVersion 14
        targetSdkVersion 19
        versionCode 1
        versionName "1.0"
    }

    buildTypes {
        debug {
            debuggable true
        }
    }
}

After Android Studio synced Gradle with project files and reinstalled an application, the debugging start working.