Caused by: java.lang.ClassCastException: android.widget.LinearLayout$LayoutParams

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/ll"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >

<RelativeLayout
android:id="@+id/rl"
android:layout_width="match_parent"
android:layout_height="match_parent">

以上是布局文件代码，我想在代码中重新设置rl的宽度

RelativeLayout relativeLayout = (RelativeLayout)this.findViewById(R.id.rl);
RelativeLayout.LayoutParams param = new RelativeLayout.LayoutParams(100, LayoutParams.MATCH_PARENT);
relativeLayout.setLayoutParams(param);

就会报这个错 Caused by: java.lang.ClassCastException: android.widget.LinearLayout$LayoutParams cannot be cast to android.widget.LinearLayout$LayoutParams 。

解决方法：relativeLayout 是LinearLayout的子控件，它的LayoutParams 应该是LinearLayout给他的。所以应该是LinearLayout.LayoutParam 。如果relativeLayout 有子控件的话，那它的子控件用的的就是relativeLayout 给他们的，才是RelativeLayout.LayoutParam。