View 处理程序未提取要查看的数据

我试图使用处理程序将消息传递给

视图
类；但我不知道我错在哪里。请纠正我。从处理程序获取值后，我从未使用画布进行绘制

提前谢谢

运行此程序后，我的日志cat在
onDraw
方法上显示
NullPointerException
。因此无法绘制线条

public class List extends Activity{

Handler handler=new Handler();
Message msg=new Message();
Bundle bundle=new Bundle();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(new TestView(this));
    bundle.putFloat("x1", 10);
    bundle.putFloat("y1", 10);
    bundle.putFloat("x2", 100);
    bundle.putFloat("y2", 100);
    msg.setData(bundle);
    handler.sendMessage(msg);

}


}

 class TestView extends View {

Paint p;
float x1;
float y1;
float x2;
float y2;

public TestView(Context context) {
    super(context);
    Paint p=new Paint();
    p.setColor(Color.BLUE);
    Handler handler=new Handler(){

        @Override
        public void handleMessage(Message msg) {
            Looper.prepare();
            Bundle bundle=msg.getData();
            x1=bundle.getFloat("x1");
            y1=bundle.getFloat("y1");
            x2=bundle.getFloat("x2");
            y2=bundle.getFloat("y2");
            Looper.loop();
        }

    };

}



boolean isDrawing=true;

@Override
protected void onDraw(Canvas canvas) {

      canvas.drawLine(x1, y1, x2, y2, p);

    invalidate();
}


}

处理程序总是只连接到一个线程，除非并直到我们没有线程，否则它无法工作。i、 e在主线程和后台线程之间发送或接收数据

视图类的正确程序应如下所示：

public class List extends Activity{


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(new TestView(this));


}


}

 class TestView extends View {


Bitmap bitmap=Bitmap.createBitmap(1000, 1000, Config.ARGB_8888);
Canvas canvas=new Canvas(bitmap);
Paint p=new Paint();


Handler handler=new Handler(){

    @Override
    public void handleMessage(Message msg) {

        p.setColor(Color.BLUE);
        Bundle bundle=msg.getData();
        String name=bundle.getString("Name");
        Toast.makeText(getContext(), name, Toast.LENGTH_LONG).show();



    }

};

public TestView(Context context) {
    super(context);
    Paint p=new Paint();
    p.setColor(Color.BLUE);
    new Thread(){
        public void run(){

            Message msg=new Message();
            Bundle bundle=new Bundle();
            Bundle bundle1=new Bundle();
            Looper.prepare();
            bundle.putString("Name", "Nishant");
            bundle1.putString("Name", "Neha");
            msg.setData(bundle);
            handler.sendMessage(msg);
            Message m1=new Message();
            m1.setData(bundle1);
            handler.sendMessage(m1);




        }
    }.start();


}


@Override
protected void onDraw(Canvas canvas) {


}





}