（手写笔）android中通过ondraw完成手写笔

手写笔：首先一定是触摸屏幕完成的。注意一般绘制没有规则的图形都是用path完成

主要是保存开始坐标和结束坐标moveTo（）；lineTo（）；

1.在一个类中完成自定义控件

package com.qn.game;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PaintFlagsDrawFilter;
import android.graphics.Path;
import android.graphics.Paint.Style;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceHolder.Callback;
import android.view.SurfaceView;
public class GameView2 extends SurfaceView implements Callback,Runnable{
 private Paint paint=null;
 private SurfaceHolder holder=null;
 private boolean flag=true;
 Canvas canvas=null;
 private Path path;
 public GameView2(Context context) {
  super(context);
  setFocusable(true);
  paint=new Paint();
  path=new Path();
   holder=this.getHolder();//得到SurfaceHolder对象，SurfaceHolder
  //就是指向SurfaceView的指针，SurfaceView就相当于电视机SurfaceHolder就相当于指向电视机
  //的遥控器，以后要就可以通过SurfaceHolder控制SurfaceView
  holder.addCallback(this);//在SurfaceHolder上面注册一个监听
  
 }
 public void run() {
  while(flag){
   drawView();  
   try {
    Thread.sleep(50);
   } catch (Exception e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   }
  }
 }
 int x=0;
 private void drawView() {
        try{
   if(holder!=null){
   canvas=holder.lockCanvas();//锁定的面板在这个锁定面板中就可以绘制了，这个地方
   canvas.setDrawFilter(new PaintFlagsDrawFilter(0,Paint.ANTI_ALIAS_FLAG
     |Paint.FILTER_BITMAP_FLAG));
  //体现二级缓存第地方
          paint.setColor(Color.GREEN);
          paint.setStyle(Style.STROKE);
          paint.setStrokeWidth(5);
         // canvas.drawCircle(200, 200, x++, paint);
          canvas.drawPath(path, paint);
   }
  }catch (Exception e) {
   e.printStackTrace();
  }
  finally{
   if(canvas!=null){
          holder.unlockCanvasAndPost(canvas);//画好之后解除锁定并且发送，把当前画好的界面发送到View上
   }
  }
 }
 public void surfaceChanged(SurfaceHolder holder, int format, int width,
   int height) {//当前view改变的时候创建的方法。
  
 }
 public void surfaceCreated(SurfaceHolder holder) {//当前view创建完成后调用的方法
  new Thread(this).start();
 }
 public void surfaceDestroyed(SurfaceHolder holder) {//当前view销毁是执行的方法
  flag=false;
 }
 @Override
 public boolean onTouchEvent(MotionEvent event) {
  switch (event.getAction()) {//手按下去抬起来的瞬间
  case MotionEvent.ACTION_DOWN:
   path.moveTo(event.getX(), event.getY());
   break;
  case MotionEvent.ACTION_MOVE:
   path.lineTo(event.getX(), event.getY());
   break;
  default:
   break;
  }
           invalidate();
  return true;
 }
 
}

2.在activity中调用