Multiple dex files define Landroid/support/v4/accessibilityservice/AccessibilityServiceInfoCompat

Run gradle -q dependencies (or gradle -q :projectName:dependencies) to generate a dependency report. You should see where r7 is coming from, such as:

compile - Classpath for compiling the main sources.
+--- com.commonsware.cwac:camera-v9:0.5.4
|    +--- com.actionbarsherlock:actionbarsherlock:4.4.0
|    |    \--- com.google.android:support-v4:r7
|    +--- com.commonsware.cwac:camera:0.5.4
|    \--- com.android.support:support-v4:18.0.+ -> 18.0.0
\--- com.android.support:support-v4:18.0.+ -> 18.0.0

Then, use the exclude directive to block that dependency. In my case, it is coming from my CWAC-Camera library, and so I use:

dependencies {
    compile('com.commonsware.cwac:camera-v9:0.5.4') {
      exclude module: 'support-v4'
    }

    compile 'com.android.support:support-v4:18.0.+'
}

(where the second compile statement indicates what version you actually want)

That should clear matters up, as you will see if you run the dependency report again:

compile - Classpath for compiling the main sources.
+--- com.commonsware.cwac:camera-v9:0.5.4
|    +--- com.actionbarsherlock:actionbarsherlock:4.4.0
|    \--- com.commonsware.cwac:camera:0.5.4
\--- com.android.support:support-v4:18.0.+ -> 18.0.0

I solved similar error by adding following piece of code to my build.gradle file inside the android block.

android {
    dexOptions {
        preDexLibraries = false
    }
}

Since A picture is worth a thousand words

To make it easier and faster to get this task done with beginners like me. this is the screenshots that shows the answer posted by @edsappfactory.com that worked for me:

First open the Gradle view on the right side of Androidstudio, in your app's item go to Tasks then Android then right-click androidDependencies then choose Run:

Second you will see something like this :

The main reason i posted this that it was not easy to know where to execute a gradle task or the commands posted above. So this is where to excute them as well.

SO, to execute gradle command:

First:

Second:

Easy as it is.

Thats it.

Thank you.