Button为何一旦添加监听setOnClickListener之后就抛异常了呢？
我在自定义的一个View上添加了一个Button，添加之后很正常，但问题是一旦为这个Button添加监听后，程序就挂了，控制台抛异常，琢磨半天没明白，还请坛友看看
Activity类：

public class ActivityMain extends Activity {


private Button btnOK;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        btnOK = (Button)findViewById(R.id.btn);
        btnOK.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {


}
});
        this.setContentView(R.layout.main);
        
    }
}

layout：

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
    
    <com.app.ViewMain
android:layout_width="fill_parent"
android:layout_height="fill_parent"/>
<TextView  
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_x="100dip"
android:layout_y="100dip"
    android:text="@string/hello"/>
<Button android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="OK"
android:id="@+id/btn"/> 
</FrameLayout>

ViewMain:

public class ViewMain extends View {

public ViewMain(Context context, AttributeSet attrs) {

super(context, attrs);


}

@Override
protected void onDraw(Canvas canvas) {
canvas.drawColor(Color.WHITE);
super.onDraw(canvas);
}

}

问题就来自Activity中的

        btnOK.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {


}
});

不添加这段代码，程序没问题，但一旦添加，程序就挂了

LogCat就会抛出如下信息：

01-26 15:03:17.669: ERROR/AndroidRuntime(2197): FATAL EXCEPTION: main
01-26 15:03:17.669: ERROR/AndroidRuntime(2197): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.app/com.app.ActivityMain}: java.lang.NullPointerException
01-26 15:03:17.669: ERROR/AndroidRuntime(2197):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
01-26 15:03:17.669: ERROR/AndroidRuntime(2197):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
01-26 15:03:17.669: ERROR/AndroidRuntime(2197):     at android.app.ActivityThread.access$2300(ActivityThread.java:125)
01-26 15:03:17.669: ERROR/AndroidRuntime(2197):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
01-26 15:03:17.669: ERROR/AndroidRuntime(2197):     at android.os.Handler.dispatchMessage(Handler.java:99) 
 
01-26 15:03:17.669: ERROR/AndroidRuntime(2197):     at android.os.Looper.loop(Looper.java:123)
01-26 15:03:17.669: ERROR/AndroidRuntime(2197):     at android.app.ActivityThread.main(ActivityThread.java:4627)
01-26 15:03:17.669: ERROR/AndroidRuntime(2197):     at java.lang.reflect.Method.invokeNative(Native Method)
01-26 15:03:17.669: ERROR/AndroidRuntime(2197):     at java.lang.reflect.Method.invoke(Method.java:521)
01-26 15:03:17.669: ERROR/AndroidRuntime(2197):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
01-26 15:03:17.669: ERROR/AndroidRuntime(2197):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
01-26 15:03:17.669: ERROR/AndroidRuntime(2197):     at dalvik.system.NativeStart.main(Native Method)
01-26 15:03:17.669: ERROR/AndroidRuntime(2197): Caused by: java.lang.NullPointerException
01-26 15:03:17.669: ERROR/AndroidRuntime(2197):     at com.app.ActivityMain.onCreate(ActivityMain.java:19)
01-26 15:03:17.669: ERROR/AndroidRuntime(2197):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
01-26 15:03:17.669: ERROR/AndroidRuntime(2197):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
01-26 15:03:17.669: ERROR/AndroidRuntime(2197):     ... 11 more

[解决办法]
btnOK = (Button)findViewById(R.id.btn);
btnOK.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {


}
});
this.setContentView(R.layout.main);
顺序错了，应该是：
this.setContentView(R.layout.main);
btnOK = (Button)findViewById(R.id.btn);
btnOK.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {


}
});


[解决办法]
at com.app.ActivityMain.onCreate(ActivityMain.java:19)

你主程序的19行出错了，你自己看一下吧。
[解决办法]
老大，你不先设置this.setContentView(R.layout.main);，去哪找(Button)findViewById(R.id.btn);的btn id号啊
[解决办法]

引用:

哎，惭愧惭愧....呵呵呵

呵呵，这种问题属于一时笔误吧。
------解决方案--------------------

看着的确感觉别扭，setview感觉位置靠后了