Fix memory leak (#210)

* Configure LeakCanary in the sample project
* Clean listener references in every single point where permission requests end

dexter/src/main/java/com/karumi/dexter/DexterInstance.java

@@ -125,6 +125,7 @@ void onActivityReady(Activity activity) {
    */
   void onActivityDestroyed() {
     isRequestingPermission.set(false);
+    listener = EMPTY_LISTENER;
   }
 
   /**
@@ -322,6 +323,7 @@ private void checkMultiplePermissions(final MultiplePermissionsListener listener
           }
           isRequestingPermission.set(false);
           listener.onPermissionsChecked(report);
+          DexterInstance.this.listener = EMPTY_LISTENER;
         }
       });
     } else {

dexter/src/test/java/com/karumi/dexter/DexterInstanceTest.java

@@ -132,6 +132,7 @@ public void onCheckPermissionMoreThanOnceThenThrowException() {
   }
 
   @Test public void onPermissionFailedByRuntimeExceptionThenNotifiesListener() {
+    givenPermissionIsChecked(ANY_PERMISSION, PackageManager.PERMISSION_DENIED);
     givenARuntimeExceptionIsThrownWhenPermissionIsChecked(ANY_PERMISSION);
     givenShouldShowRationaleForPermission(ANY_PERMISSION);
 

sample/build.gradle

@@ -34,6 +34,7 @@ dependencies {
   implementation 'com.android.support:appcompat-v7:27.1.1'
   implementation 'com.android.support:design:27.1.1'
   implementation 'com.jakewharton:butterknife:8.6.0'
+  implementation 'com.squareup.leakcanary:leakcanary-android:1.5.4'
   annotationProcessor 'com.jakewharton:butterknife-compiler:8.6.0'
   implementation project(':dexter')
   androidTestImplementation 'com.android.support.test:runner:0.5'

sample/src/main/AndroidManifest.xml

@@ -23,6 +23,7 @@
   <uses-permission android:name="android.permission.RECORD_AUDIO"/>
 
   <application
+      android:name=".SampleApplication"
       android:allowBackup="true"
       android:label="@string/app_name"
       android:icon="@mipmap/ic_logo_karumi"

sample/src/main/java/com/karumi/dexter/sample/SampleApplication.java

@@ -0,0 +1,19 @@
+package com.karumi.dexter.sample;
+
+import android.app.Application;
+import com.squareup.leakcanary.LeakCanary;
+
+public class SampleApplication extends Application {
+
+  @Override public void onCreate() {
+    super.onCreate();
+    configureLeakCanary();
+  }
+
+  private void configureLeakCanary() {
+    if (LeakCanary.isInAnalyzerProcess(this)) {
+      return;
+    }
+    LeakCanary.install(this);
+  }
+}