的FrameLayout到RelativeLayout的ClassCastException异常，即

在我的应用程序，我有其中有一个布局RelativeLayout ，而我想在运行时以编程方式设置页边距。但是，当我做到这一点，它给了我ClassCastException说FrameLayout无法投射到RelativeLayout 。我没有使用任何的FrameLayout，也没有进口FrameLayout 。不过问题依然存在。我使用的XML是：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/rl_root"
android:background="@color/menu_bg"
android:layout_width="wrap_content"
android:layout_height="fill_parent" >

<RelativeLayout
    android:id="@+id/ll_lhs_menu"
    android:layout_width="300dip"
    android:layout_height="fill_parent"
    android:background="@color/menu_bg"
    android:orientation="vertical">

    .....

</RelativeLayout>

<RelativeLayout
    android:id="@+id/rl_right"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:layout_alignParentRight="true"
    android:background="@drawable/capture_port"
    android:scrollbars="none" >

    ....

</RelativeLayout>

</RelativeLayout>

这是我的onCreate，我设置页边距父布局：

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.menu);

 _rootLayout = (RelativeLayout) findViewById(R.id.rl_root);
RelativeLayout.LayoutParams _rootLayoutParams = new RelativeLayout.LayoutParams(_rootLayout.getWidth(), _rootLayout.getHeight());
_rootLayoutParams.setMargins(300, 0, 300, 0);
_rootLayout.setLayoutParams(_rootLayoutParams);
}

这里是logcat的：

    07-18 21:12:39.410: E/AndroidRuntime(7663): FATAL EXCEPTION: main
    07-18 21:12:39.410: E/AndroidRuntime(7663): java.lang.ClassCastException: android.widget.RelativeLayout$LayoutParams cannot be cast to android.widget.FrameLayout$LayoutParams
    07-18 21:12:39.410: E/AndroidRuntime(7663):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:268)
    07-18 21:12:39.410: E/AndroidRuntime(7663):     at android.view.View.measure(View.java:10828)
    07-18 21:12:39.410: E/AndroidRuntime(7663):     at android.widget.LinearLayout.measureVertical(LinearLayout.java:764)
    07-18 21:12:39.410: E/AndroidRuntime(7663):     at android.widget.LinearLayout.onMeasure(LinearLayout.java:519)
    07-18 21:12:39.410: E/AndroidRuntime(7663):     at android.view.View.measure(View.java:10828)
    07-18 21:12:39.410: E/AndroidRuntime(7663):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4355)
    07-18 21:12:39.410: E/AndroidRuntime(7663):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:267)
    07-18 21:12:39.410: E/AndroidRuntime(7663):     at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:1912)
    07-18 21:12:39.410: E/AndroidRuntime(7663):     at android.view.View.measure(View.java:10828)
    07-18 21:12:39.410: E/AndroidRuntime(7663):     at android.view.ViewRoot.performTraversals(ViewRoot.java:960)
    07-18 21:12:39.410: E/AndroidRuntime(7663):     at android.view.ViewRoot.handleMessage(ViewRoot.java:2062)
    07-18 21:12:39.410: E/AndroidRuntime(7663):     at android.os.Handler.dispatchMessage(Handler.java:99)
    07-18 21:12:39.410: E/AndroidRuntime(7663):     at android.os.Looper.loop(Looper.java:132)
    07-18 21:12:39.410: E/AndroidRuntime(7663):     at android.app.ActivityThread.main(ActivityThread.java:4128)
    07-18 21:12:39.410: E/AndroidRuntime(7663):     at java.lang.reflect.Method.invokeNative(Native Method)
    07-18 21:12:39.410: E/AndroidRuntime(7663):     at java.lang.reflect.Method.invoke(Method.java:491)
    07-18 21:12:39.410: E/AndroidRuntime(7663):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
    07-18 21:12:39.410: E/AndroidRuntime(7663):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
    07-18 21:12:39.410: E/AndroidRuntime(7663):     at dalvik.system.NativeStart.main(Native Method)

我要去哪里错了？

Answer 1:

尝试设置FrameLayout.LayoutParams，而是如果RelativeLayout.LayoutParams。当您在运行时设置布局参数，可以你必须设置的那些从它的父。

因此，这将是：

FrameLayout.LayoutParams _rootLayoutParams = new FrameLayout.LayoutParams(_rootLayout.getWidth(), _rootLayout.getHeight());
_rootLayoutParams.setMargins(300, 0, 300, 0);
_rootLayout.setLayoutParams(_rootLayoutParams);

Answer 2:

有一次，我以前吃过这个错误，那是因为我想投而不是创建一个新的实例参数。我希望这有帮助。

就在这儿：

RelativeLayout.LayoutParams _rootLayoutParams = new RelativeLayout.LayoutParams(_rootLayout.getWidth(), _rootLayout.getHeight());

应该：

RelativeLayout.LayoutParams _rootLayoutParams = new RelativeLayout.LayoutParams(_rootLayout.getLayoutParams());

现在你已经从父（根）布局中的所有布局参数，你可以用它们来为您的孩子认为你正在膨胀的参数。

// Example usage:   
// viewGroup is the parent in this case whose parameters we want as a reference point.
RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(viewGroup.getLayoutParams());

// Now we can add a rule stating that we want to center our new view both horizontally and vertically in the parent (viewGroup) view.
params.addRule(RelativeLayout.CENTER_IN_PARENT);

// Add more rules here if you would like
params.addRule(newRule2);

// After all of your new parameters are laid out, assign them to the view you want them applied to  
newView.setLayoutParams(params);

// Add the view to your hierarchy and enjoy
viewGroup.addView(newView);

Answer 3:

我建议@ ID / rl_root的母公司必须是FrameLayout里未在此xml显示。 LayoutParam的类型应与其父本身并不相同。