View和SurfaceView的刷屏方式

1、View的刷屏方式

View主要是调用onDraw(Canvas canvas)方法，利用Canvas(画布)来绘制图形，再利用invalidate()/postInvalidate()方法来进行重绘，达到类刷屏的效果。

下面通过“随手指移动的小球”为例子，展示View的刷屏方式，代码如下：

继承View的MyView类：

package com.example.huawei;

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 = 100, textY = 100;

    public MyView(Context context){
        super(context);
        //setFocusable(true);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        // TODO Auto-generated method stub
        Paint paint = new Paint();
        paint.setColor(Color.WHITE);
        canvas.drawCircle(textX, textY, 20, paint);
        super.onDraw(canvas);
    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        // TODO Auto-generated method stub
        return super.onKeyDown(keyCode, event);
    }

    @Override
    public boolean onKeyUp(int keyCode, KeyEvent event) {
        // TODO Auto-generated method stub
        return super.onKeyUp(keyCode, event);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        // TODO Auto-generated method stub
        int x = (int)event.getX();
        int y = (int)event.getY();
        if(event.getAction() == MotionEvent.ACTION_DOWN){
            textX = x;
            textY = y;
        }else if(event.getAction() == MotionEvent.ACTION_UP){
            textX = x;
            textY = y;
        }else if(event.getAction() == MotionEvent.ACTION_MOVE){
            textX = x;
            textY = y;
        }
        invalidate();
        //return super.onTouchEvent(event);
        return true;
    }
}

使用MyView类的MainActivity类：

package com.example.huawei;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;

public class MainActivity extends Activity{

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

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }
}

随手指移动的效果图，如下所示：

继承View类的MyView类，刷屏主要是通过重写onDraw(Canvas canvas)方法来实现的。View的画图方式，主要是在onDraw()方法内，利用画布canvas进行绘制。
但是，onDraw()方法只会在View视图开始创建的时候，执行一遍而已。要想在新的画布上，进行图形绘制，需要调用View内的两个方法：
invalidate()
postInvalidate()
上面两个调用onDraw()进行重新绘制画布的方法，其主要区别：
invalidate()方法不能在当前自己创建的子线程中循环调用执行(可以在系统的UI线程中执行)。
postInvalidate()方法可以在当前创建的子线程中循环调用。
如果不在当前View创建线程循环重绘画布的话，这两种重绘画布的函数，并没有什么区别，都可以使用。

2、SurfaceView的刷屏方式
继承SurfaceView类的执行类，使用SurfaceHolder类的对象的lockCanvas()方法，获得画布canvas，在上面进行图形绘制。

下面的例子，是利用SurfaceView类，来实现“随手指移动的小球”，代码如下：

package com.example.huawei;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.SurfaceHolder.Callback;

public class MySurfaceView extends SurfaceView implements Callback{
    private SurfaceHolder surfaceHolder;
    private Paint paint;
    private int textX = 100, textY = 100;

    public MySurfaceView(Context context){
        super(context);
        //实例化SurfaceHolder
        surfaceHolder = this.getHolder();
        //为surfaceHolder添加状态监听
        surfaceHolder.addCallback(this);
        //实例化一个画笔
        paint = new Paint();
        //设置画笔颜色为白色
        paint.setColor(Color.WHITE);
    }

    @Override
    public void surfaceChanged(SurfaceHolder arg0, int arg1, int arg2, int arg3) {
        // TODO Auto-generated method stub

    }

    @Override
    public void surfaceCreated(SurfaceHolder arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void surfaceDestroyed(SurfaceHolder arg0) {
        // TODO Auto-generated method stub

    }

    public void myDraw(){
        Canvas canvas = surfaceHolder.lockCanvas();
        canvas.drawCircle(textX, textY, 20, paint);
        surfaceHolder.unlockCanvasAndPost(canvas);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        // TODO Auto-generated method stub
        textX = (int)event.getX();
        textY = (int)event.getY();
        myDraw();
        return true;
    }
}

使用MySurfaceView类的MainActivity类：

package com.example.huawei;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;

public class MainActivity extends Activity{

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

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }
}

随手指移动的效果图，如下所示：

从上面的效果图可以看到，MySurfaceView类不断调用myDraw(0方法进行图形绘制，但是，canvas并没有换，还是原来的画布。因此，在上面绘制的小球越来越多。这是因为MySurfaceView类没有更换canvas，没有进行刷屏。
对于SurfaceView类的刷屏方式，主要有四种：

2.1、每次绘画之前，在画布上，填充一种颜色，将先前绘制的图形覆盖掉：

    public void myDrawColor() {
        Canvas canvas = surfaceHolder.lockCanvas();
        canvas.drawColor(Color.BLACK);
        canvas.drawCircle(textX, textY, 20, paint);
        surfaceHolder.unlockCanvasAndPost(canvas);
    }

2.2、每次绘画之前，在画布上，指定RGB颜色来填充画布(类似于方法一)，将先前绘制的图形覆盖掉：

    public void myDrawRGB() {
        Canvas canvas = surfaceHolder.lockCanvas();
        canvas.drawRGB(0, 0, 0);
        canvas.drawCircle(textX, textY, 20, paint);
        surfaceHolder.unlockCanvasAndPost(canvas);
    }

2.3、每次绘画之前，绘制一个等同于屏幕大小的Rect图形，将先前绘制的图形覆盖掉：

    public void myDrawRect() {
        Canvas canvas = surfaceHolder.lockCanvas();
        canvas.drawRect(0,0,this.getWidth(),this.getHeight(),paint);
        canvas.drawCircle(textX, textY, 20, paint);
        surfaceHolder.unlockCanvasAndPost(canvas);
    }

2.4、每次绘图之前，绘制一张等同于屏幕大小的图片，将先前绘制的图形覆盖掉：

    public void myDrawBitmap() {
        Canvas canvas = surfaceHolder.lockCanvas();
        canvas.drawBitmap(bitmap, 0, 0, paint);
        canvas.drawCircle(textX, textY, 20, paint);
        surfaceHolder.unlockCanvasAndPost(canvas);
    }

使用SurfaceView的刷图方式，实现“随手指移动的小球”，其主要的实现代码如下：

package com.example.huawei;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.SurfaceHolder.Callback;

public class MySurfaceView extends SurfaceView implements Callback{
    private SurfaceHolder surfaceHolder;
    private Paint paint;
    private int textX = 100, textY = 100;
    private Bitmap bitmap;

    public MySurfaceView(Context context){
        super(context);
        //实例化SurfaceHolder
        surfaceHolder = this.getHolder();
        //为surfaceHolder添加状态监听
        surfaceHolder.addCallback(this);
        //实例化一个画笔
        paint = new Paint();
        //设置画笔颜色为白色
        paint.setColor(Color.WHITE);
        BitmapDrawable bitmapDrawable = (BitmapDrawable)(context.getResources().getDrawable(R.drawable.ic_launcherbit));
        bitmap = bitmapDrawable.getBitmap();
    }

    @Override
    public void surfaceChanged(SurfaceHolder arg0, int arg1, int arg2, int arg3) {
        // TODO Auto-generated method stub

    }

    @Override
    public void surfaceCreated(SurfaceHolder arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void surfaceDestroyed(SurfaceHolder arg0) {
        // TODO Auto-generated method stub

    }

    public void myDraw(){
        Canvas canvas = surfaceHolder.lockCanvas();
        canvas.drawCircle(textX, textY, 20, paint);
        surfaceHolder.unlockCanvasAndPost(canvas);
    }

    public void myDrawColor() {
        Canvas canvas = surfaceHolder.lockCanvas();
        canvas.drawColor(Color.BLACK);
        canvas.drawCircle(textX, textY, 20, paint);
        surfaceHolder.unlockCanvasAndPost(canvas);
    }

    public void myDrawRGB() {
        Canvas canvas = surfaceHolder.lockCanvas();
        canvas.drawRGB(0, 0, 0);
        canvas.drawCircle(textX, textY, 20, paint);
        surfaceHolder.unlockCanvasAndPost(canvas);
    }

    public void myDrawRect() {
        Canvas canvas = surfaceHolder.lockCanvas();
        canvas.drawRect(0,0,this.getWidth(),this.getHeight(),paint);
        canvas.drawCircle(textX, textY, 20, paint);
        surfaceHolder.unlockCanvasAndPost(canvas);
    }

    public void myDrawBitmap() {
        Canvas canvas = surfaceHolder.lockCanvas();
        canvas.drawBitmap(bitmap, 0, 0, paint);
        canvas.drawCircle(textX, textY, 20, paint);
        surfaceHolder.unlockCanvasAndPost(canvas);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        // TODO Auto-generated method stub
        textX = (int)event.getX();
        textY = (int)event.getY();
        myDrawBitmap();
        return true;
    }
}

使用MySurfaceView类的MainActivity类：

package com.example.huawei;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;

public class MainActivity extends Activity{

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

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }
}

随手指移动的效果图，如下所示：