android - 使用 LayoutParams 以编程方式从 FrameLayout 中删除边距

Question

我有一个如下所示的 FrameLayout:

 <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>

但是，当我以编程方式更改边距时，我得到了 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);

这是我正在尝试的方式:

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

这是 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)

我不明白这里如何涉及RelativeLayout？

Answer 1

LayoutParams 类由父级而不是子级指定。影响 FrameLayout 的 LayoutParams 是一个 RelativeLayout.LayoutParams。影响 FrameLayout 的 child 的 LayoutParams 将是 FrameLayout.LayoutParams。