Rimuovere periodicamente margine da FrameLayout con LayoutParams - android, relativelayout, classcastexception, framelayout

Ho un FrameLayout che assomiglia a questo:

 <RelativeLayout
android:layout_width="match_parent"
android:layout_height="wrap_content">

<FrameLayout
android:layout_marginTop="56dp"
android:layout_marginBottom="50dp"
android:id="@+id/main_frag"
android:layout_width="match_parent"
android:layout_height="match_parent" />

// other stuff


</RelativeLayout>

Tuttavia, quando cambio i margini programmaticamente ottengo una ClassCastException.

        FrameLayout fl = (FrameLayout) findViewById(R.id.main_frag);
FrameLayout.LayoutParams params = (FrameLayout.LayoutParams) fl.getLayoutParams();
params.setMargins(50, 0, 0, 0);
fl.setLayoutParams(params);

Ecco come sto provando:

        FrameLayout fl = (FrameLayout) findViewById(R.id.main_frag);
FrameLayout.LayoutParams params = (FrameLayout.LayoutParams) fl.getLayoutParams();
params.setMargins(50, 0, 0, 0);
fl.setLayoutParams(params);

Qui è LogCat:

04-25 16:18:08.385: E/AndroidRuntime(27682): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.---.---/com.------.---.MainFragmentActivity}: java.lang.ClassCastException: android.widget.RelativeLayout$LayoutParams cannot be cast to android.widget.FrameLayout$LayoutParams
04-25 16:18:08.385: E/AndroidRuntime(27682):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2314)
04-25 16:18:08.385: E/AndroidRuntime(27682):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2388)
04-25 16:18:08.385: E/AndroidRuntime(27682):    at android.app.ActivityThread.access$800(ActivityThread.java:148)
04-25 16:18:08.385: E/AndroidRuntime(27682):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1292)
04-25 16:18:08.385: E/AndroidRuntime(27682):    at android.os.Handler.dispatchMessage(Handler.java:102)
04-25 16:18:08.385: E/AndroidRuntime(27682):    at android.os.Looper.loop(Looper.java:135)
04-25 16:18:08.385: E/AndroidRuntime(27682):    at android.app.ActivityThread.main(ActivityThread.java:5312)
04-25 16:18:08.385: E/AndroidRuntime(27682):    at java.lang.reflect.Method.invoke(Native Method)
04-25 16:18:08.385: E/AndroidRuntime(27682):    at java.lang.reflect.Method.invoke(Method.java:372)
04-25 16:18:08.385: E/AndroidRuntime(27682):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
04-25 16:18:08.385: E/AndroidRuntime(27682):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)
04-25 16:18:08.385: E/AndroidRuntime(27682): Caused by: java.lang.ClassCastException: android.widget.RelativeLayout$LayoutParams cannot be cast to android.widget.FrameLayout$LayoutParams
04-25 16:18:08.385: E/AndroidRuntime(27682):    at com.---.---.MainFragmentActivity.onCreate(MainFragmentActivity.java:81)
04-25 16:18:08.385: E/AndroidRuntime(27682):    at android.app.Activity.performCreate(Activity.java:5953)
04-25 16:18:08.385: E/AndroidRuntime(27682):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1128)
04-25 16:18:08.385: E/AndroidRuntime(27682):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2267)

Non capisco come RelativeLayout è coinvolto qui?

risposte:

Il LayoutParams la classe è dettata dal genitore, non dal figlio. Il LayoutParams che influenzano il FrameLayout è un RelativeLayout.LayoutParams. Il LayoutParams che colpisce il bambino del FrameLayout sarebbe un FrameLayout.LayoutParams.