package com.example.ex4_4;import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.View;public class MyView extends View {private int textX=20,textY=20;/*** 重写父类构造函数* @param context*/public MyView(Context context) {super(context);//设置焦点setFocusable(true);}/**** 重写按键按下事件* @param  keyCode 当前用户点击的按键* @param  event 按键的动作事件队列，此类还定义了很多静态常量键值*/@Overridepublic boolean onKeyDown(int keyCode, KeyEvent event) {//判定用户按下的键值是否方向键的"上下左右"键if(keyCode==KeyEvent.KEYCODE_DPAD_UP){//"上"按键被点击，应该让文本的Y坐标变小textY-=2;}else if(keyCode==KeyEvent.KEYCODE_DPAD_DOWN){//"下"按键被点击，应该让文本的Y坐标变大textY+=2;}else if(keyCode==KeyEvent.KEYCODE_DPAD_LEFT){//"左"按键被点击，应该让文本的X坐标变小textX-=2;}else if(keyCode==KeyEvent.KEYCODE_DPAD_RIGHT){//"右"按键被点击，应该让文本的X坐标变大textX+=2;}return super.onKeyDown(keyCode, event);}/*** 重写按键抬起事件*/@Overridepublic boolean onKeyUp(int keyCode, KeyEvent event) {//invalidate();不能在当前子线程中循环调用执行//postInvalidate(); 可以在子线程中循环调用执行invalidate();//重新绘制画布return super.onKeyUp(keyCode, event);}/*** 重写触屏事件函数*/@Overridepublic boolean onTouchEvent(MotionEvent event) {//获取用户手指触屏的X坐标赋值与文本的X坐标int x = (int)event.getX();//获取用户手指触屏的Y坐标赋值与文本的Y坐标int y = (int)event.getY();textX=x;textY=y;//重绘画布
        invalidate();return true;}/*** 重写父类绘图函数*/@Overrideprotected void onDraw(Canvas canvas) {//创建一个画笔实例Paint paint = new Paint();//设置画笔颜色
        paint.setColor(Color.WHITE);//设置画笔文本大小paint.setTextSize(18);//绘制文本canvas.drawText("Hi，你好！", textX, textY, paint);super.onDraw(canvas);}}

public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(new MyView(this));
}
}

android:theme="@android:style/Theme.Black.NoTitleBar.Fullscreen"