setLayoutParams（）方法不起作用

我正在制作一个代码，根据应用程序提供的屏幕大小来改变其大小 . 它通过View的onSizeChanged（）和onDraw（）方法获取整个宽度和高度（或其适当的视图的w和h） .

它在另一个代码中工作得很好但是现在每当我尝试输入命令'setLayoutParams（）时它都显示错误消息你能帮我解决这个问题吗？ setLayoutParams（）实际上在代码中的任何地方都不起作用 . 下面是主类代码 .

public class ManipulateDesign extends Activity {
    private LinearLayout ll;
    private ScrollView sv;
    private TextView tv;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        ll = (LinearLayout) findViewById(R.id.ll);
        sv = (ScrollView) findViewById(R.id.sv);
        tv = new TextView(this);

        tv.setText("You're in the first ScrollView\n" +
                "- Living Universe \n" +
                "Wish (upon a star) Hope to (be again)\n" +
                "The one you find, when all is done and through!\n" +
                "If all, made a wish to save, the star would it be in vain?\n" +
                "So much it holds, too dear to part, many ways to see the light of answers!\n" +
                "For all was once, just taken away, that one hope all disappeared so none can break nor brittle my heart\n" +
                "no, never again, until the end");

        sv.addView(tv);
        ChangeSizeView csv = new ChangeSizeView(getApplicationContext());
        ll.addView(csv);
    }

    class ChangeSizeView extends View{
        int newWidth;
        int newHeight;

        public ChangeSizeView(Context context) {
            super(context);
        }

        @Override
        protected void onSizeChanged(int w, int h, int oldw, int oldh) {
            newWidth = w;
            newHeight = h;
            super.onSizeChanged(w, h, oldw, oldh);
        }

        @Override
        protected void onDraw(Canvas canvas) {
            // THIS COMMAND MAKES AN ERROR(not just in this method but anywhere in the entire code) BUT WORKED WELL IN ANOTHER CODE     
            sv.setLayoutParams(new LayoutParams(LayoutParams.WRAP_CONTENT, (newHeight - 100)));         

            super.onDraw(canvas);
        }
    }
}

这是我的main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:id="@+id/ll"
    >
    <ScrollView android:id="@+id/sv"
                android:layout_height="wrap_content"
                android:layout_width="wrap_content">
    </ScrollView>
</LinearLayout>

这是显示错误消息的logcat徽标

04-11 06:39:52.148: ERROR/AndroidRuntime(2952): FATAL EXCEPTION: main
04-11 06:39:52.148: ERROR/AndroidRuntime(2952): java.lang.ClassCastException: android.view.ViewGroup$LayoutParams
04-11 06:39:52.148: ERROR/AndroidRuntime(2952):     at android.widget.LinearLayout.measureVertical(LinearLayout.java:355)
04-11 06:39:52.148: ERROR/AndroidRuntime(2952):     at android.widget.LinearLayout.onMeasure(LinearLayout.java:304)
04-11 06:39:52.148: ERROR/AndroidRuntime(2952):     at android.view.View.measure(View.java:8171)
04-11 06:39:52.148: ERROR/AndroidRuntime(2952):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3132)
04-11 06:39:52.148: ERROR/AndroidRuntime(2952):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:245)
04-11 06:39:52.148: ERROR/AndroidRuntime(2952):     at android.view.View.measure(View.java:8171)
04-11 06:39:52.148: ERROR/AndroidRuntime(2952):     at android.widget.LinearLayout.measureVertical(LinearLayout.java:526)
04-11 06:39:52.148: ERROR/AndroidRuntime(2952):     at android.widget.LinearLayout.onMeasure(LinearLayout.java:304)
04-11 06:39:52.148: ERROR/AndroidRuntime(2952):     at android.view.View.measure(View.java:8171)
04-11 06:39:52.148: ERROR/AndroidRuntime(2952):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3132)
04-11 06:39:52.148: ERROR/AndroidRuntime(2952):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:245)
04-11 06:39:52.148: ERROR/AndroidRuntime(2952):     at android.view.View.measure(View.java:8171)
04-11 06:39:52.148: ERROR/AndroidRuntime(2952):     at android.view.ViewRoot.performTraversals(ViewRoot.java:801)
04-11 06:39:52.148: ERROR/AndroidRuntime(2952):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1727)
04-11 06:39:52.148: ERROR/AndroidRuntime(2952):     at android.os.Handler.dispatchMessage(Handler.java:99)
04-11 06:39:52.148: ERROR/AndroidRuntime(2952):     at android.os.Looper.loop(Looper.java:123)
04-11 06:39:52.148: ERROR/AndroidRuntime(2952):     at android.app.ActivityThread.main(ActivityThread.java:4627)
04-11 06:39:52.148: ERROR/AndroidRuntime(2952):     at java.lang.reflect.Method.invokeNative(Native Method)
04-11 06:39:52.148: ERROR/AndroidRuntime(2952):     at java.lang.reflect.Method.invoke(Method.java:521)
04-11 06:39:52.148: ERROR/AndroidRuntime(2952):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
04-11 06:39:52.148: ERROR/AndroidRuntime(2952):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
04-11 06:39:52.148: ERROR/AndroidRuntime(2952):     at dalvik.system.NativeStart.main(Native Method)