如何为线性布局元素设置setLayoutParams

LinearLayout

setLayoutParams()

MainActivity.java

layoutParams = new LinearLayout.LayoutParams(LayoutParams.WRAP_CONTENT, 50);
imageview1.setLayoutParams(layoutParams); // line no 50

layoutParams = new LinearLayout.LayoutParams(LayoutParams.WRAP_CONTENT, 50);
textview1.setLayoutParams(layoutParams);

layoutParams = new LinearLayout.LayoutParams(LayoutParams.FILL_PARENT,LayoutParams.WRAP_CONTENT);
listview01.setLayoutParams(layoutParams);

<?xml version=\"1.0\" encoding=\"utf-8\"?>
<LinearLayout xmlns:android=\"http://schemas.android.com/apk/res/android\"
android:orientation=\"vertical\"
android:layout_width=\"wrap_content\"
android:layout_height=\"wrap_content\"
android:stackFromBottom=\"true\"
>
<ImageView
android:id=\"@+id/imageview1\"
android:layout_width=\"wrap_content\"
android:layout_height=\"50px\"
android:background=\"@drawable/applicationbar\"
android:layout_x=\"0px\"
android:layout_y=\"0px\"
>
</ImageView>
<TextView
android:id=\"@+id/textview1\"
android:layout_width=\"wrap_content\"
android:layout_height=\"50px\"
android:text=\"TextView\"
android:layout_x=\"0px\"
android:layout_y=\"55px\"
>
</TextView>
<ListView android:id=\"@+id/ListView01\"
android:layout_width=\"fill_parent\"
android:layout_height=\"wrap_content\"
android:layout_marginLeft=\"10px\" 
android:layout_marginRight=\"10px\"
android:layout_marginTop=\"35px\" 
android:layout_marginBottom=\"40px\"
android:paddingLeft=\"0px\"
android:paddingRight=\"0px\" />
</LinearLayout>

04-19 16:47:22.221: ERROR/AndroidRuntime(3437): Uncaught handler: thread main exiting due to uncaught exception
04-19 16:47:22.221: ERROR/AndroidRuntime(3437): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.android/com.android.Listview}: java.lang.NullPointerException
04-19 16:47:22.221: ERROR/AndroidRuntime(3437):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2496)
04-19 16:47:22.221: ERROR/AndroidRuntime(3437):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512)
04-19 16:47:22.221: ERROR/AndroidRuntime(3437):     at android.app.ActivityThread.access$2200(ActivityThread.java:119)
04-19 16:47:22.221: ERROR/AndroidRuntime(3437):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863)
04-19 16:47:22.221: ERROR/AndroidRuntime(3437):     at android.os.Handler.dispatchMessage(Handler.java:99)
04-19 16:47:22.221: ERROR/AndroidRuntime(3437):     at android.os.Looper.loop(Looper.java:123)
04-19 16:47:22.221: ERROR/AndroidRuntime(3437):     at android.app.ActivityThread.main(ActivityThread.java:4363)
04-19 16:47:22.221: ERROR/AndroidRuntime(3437):     at java.lang.reflect.Method.invokeNative(Native Method)
04-19 16:47:22.221: ERROR/AndroidRuntime(3437):     at java.lang.reflect.Method.invoke(Method.java:521)
04-19 16:47:22.221: ERROR/AndroidRuntime(3437):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
04-19 16:47:22.221: ERROR/AndroidRuntime(3437):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
04-19 16:47:22.221: ERROR/AndroidRuntime(3437):     at dalvik.system.NativeStart.main(Native Method)
04-19 16:47:22.221: ERROR/AndroidRuntime(3437): Caused by: java.lang.NullPointerException
04-19 16:47:22.221: ERROR/AndroidRuntime(3437):     at com.android.Listview.onCreate(Listview.java:40)
04-19 16:47:22.221: ERROR/AndroidRuntime(3437):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
04-19 16:47:22.221: ERROR/AndroidRuntime(3437):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2459)