Android中SurfaceView和view画出触摸轨迹

一、引言
         想实现一个空白的画板，上面可以画出手滑动的轨迹，就这么一个小需求。一般就来讲就两种实现方式，view或者surfaceview。下面看看两种是如何实现的。
二、实现原理
         先简单说一下实现原理：
       （1）用一张白色的Bitmap作为画板
       （2）用canvas在bitmap上画线
       （3）为了画出平滑的曲线，要用canvas的drawPath（Path，Paint）方法。
       （4）同时使用贝塞尔曲线来使曲线更加平滑
三、View实现
直接贴代码了：

package picturegame.view; 
import android.annotation.SuppressLint; 
import android.content.Context; 
import android.graphics.Bitmap; 
import android.graphics.BitmapFactory; 
import android.graphics.Canvas; 
import android.graphics.Color; 
import android.graphics.Paint; 
import android.graphics.Paint.Style; 
import android.graphics.Path; 
import android.util.AttributeSet; 
import android.view.MotionEvent; 
import android.view.View; 
import com.winton.picturegame.R; 
 
public class GameView extends View{ 
 private Paint paint = null; // 
 private Bitmap originalBitmap = null;//原始图 
 private Bitmap new1Bitmap = null; 
 private Bitmap new2Bitmap = null; 
 private float clickX =0; 
 private float clickY=0; 
 private float startX=0; 
 private float startY=0; 
 private boolean isMove = true; 
 private boolean isClear = false; 
 private int color =Color.RED;//默认画笔颜色 
 private float strokeWidth =20f;//默认画笔宽度 
 Path mPath; 
 public GameView(Context context) { 
  this(context,null); 
  // TODO Auto-generated constructor stub 
 } 
 public GameView(Context context,AttributeSet atts) { 
  this(context,atts,0); 
  // TODO Auto-generated constructor stub 
 } 
 @SuppressWarnings("static-access") 
 public GameView(Context context,AttributeSet atts,int defStyle) { 
  super(context,atts,defStyle); 
  // TODO Auto-generated constructor stub 
  originalBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.default_pic).copy(Bitmap.Config.ARGB_8888, true);//白色的画板 
  new1Bitmap=originalBitmap.createBitmap(originalBitmap); 
  mPath=new Path(); 
 } 
 //清楚 
 @SuppressWarnings("static-access") 
 public void clear(){ 
  isClear =true; 
  new2Bitmap=originalBitmap.createBitmap(originalBitmap); 
  invalidate();//重置 
 } 
 public void setStrokeWidth(float width){ 
  this.strokeWidth=width; 
  initPaint(); 
 } 
 @Override 
 protected void onDraw(Canvas canvas) { 
  // TODO Auto-generated method stub 
  super.onDraw(canvas); 
  canvas.drawBitmap(writer(new1Bitmap),0,0, null); 
 } 
 @SuppressLint("ClickableViewAccessibility") 
 @Override 
 public boolean onTouchEvent(MotionEvent event) { 
  // TODO Auto-generated method stub 
  clickX =event.getX(); 
  clickY=event.getY(); 
  if(event.getAction()==MotionEvent.ACTION_DOWN){ 
   //手指点下屏幕时触发 
   startX=clickX; 
   startY=clickY; 
   mPath.reset(); 
   mPath.moveTo(clickX, clickY); 
//   isMove =false; 
//   invalidate(); 
//   return true; 
  } 
  else if(event.getAction()==MotionEvent.ACTION_MOVE){ 
   //手指移动时触发 
   float dx=Math.abs(clickX-startX); 
   float dy=Math.abs(clickY-startY); 
//   if(dx>=3||dy>=3){ 
    //设置贝塞尔曲线的操作点为起点和终点的一半 
    float cX = (clickX + startX) / 2; 
    float cY = (clickY + startY) / 2; 
    mPath.quadTo(startX,startY, cX, cY); 
    startX=clickX; 
    startY=clickY; 
//   } 
//   isMove =true; 
//   invalidate(); 
//   return true; 
  } 
  invalidate(); 
  return true; 
 } 
  
 public Bitmap writer(Bitmap pic){ 
  initPaint(); 
  Canvas canvas =null; 
  if(isClear){ 
   canvas=new Canvas(new2Bitmap); 
  }else{ 
   canvas=new Canvas(pic); 
  } 
   //canvas.drawLine(startX, startY, clickX, clickY, paint);//画线 
   canvas.drawPath(mPath, paint); 
  if(isClear){ 
   return new2Bitmap; 
  } 
  return pic; 
 } 
 private void initPaint(){ 
  paint = new Paint();//初始化画笔 
  paint.setStyle(Style.STROKE);//设置为画线 
  paint.setAntiAlias(true);//设置画笔抗锯齿 
  paint.setColor(color);//设置画笔颜色 
  paint.setStrokeWidth(strokeWidth);//设置画笔宽度 
 } 
  
 public void setColor(int color){ 
  this.color=color; 
  initPaint(); 
 } 
 public Bitmap getPaint(){ 
  return new1Bitmap; 
 } 
} 

看一下效果：

基本满足需求
三、surfaceView实现

package picturegame.view; 
import android.content.Context; 
import android.graphics.Bitmap; 
import android.graphics.BitmapFactory; 
import android.graphics.Canvas; 
import android.graphics.Paint; 
import android.graphics.Paint.Style; 
import android.graphics.Path; 
import android.util.AttributeSet; 
import android.view.MotionEvent; 
import android.view.SurfaceHolder; 
import android.view.SurfaceHolder.Callback; 
import android.view.SurfaceView; 
import com.winton.picturegame.R; 
public class GameViewSurface extends SurfaceView implements Callback,Runnable{ 
  
 boolean mRunning = false; 
  
 boolean mIsRunning = false; 
   
 public static final int TIME_IN_FRAME = 50; 
 private int paintColor=android.graphics.Color.WHITE;//默认画笔颜色为黑色 
 private float paintWidth=2f;//默认画笔宽度 
 private Style paintStyle=Style.STROKE;//默认画笔风格 
 private int paintAlph=255;//默认不透明 
 private Path mPath;//轨迹 
 private Paint mPaint;//画笔 
 private float startX=0.0f;//初始x 
 private float startY=0.0f;//初始Y 
 private SurfaceHolder surfaceHolder; 
 public Canvas mCanvas; 
 public boolean first=true; 
 Bitmap bg; 
 public GameViewSurface(Context context){ 
  this(context,null); 
 } 
 public GameViewSurface(Context context,AttributeSet attrs){ 
  this(context,attrs,0); 
 } 
 public GameViewSurface(Context context, AttributeSet attrs, int defStyle) { 
  super(context, attrs, defStyle); 
  // TODO Auto-generated constructor stub 
  this.setFocusable(true);//设置当前view拥有触摸事件 
  surfaceHolder=getHolder(); 
  surfaceHolder.addCallback(this); 
  mPath=new Path(); 
  initPaint(); 
  bg = BitmapFactory.decodeResource(getResources(), R.drawable.default_pic).copy(Bitmap.Config.ARGB_8888, true);//白色的画板 
 } 
  
 private void initPaint(){ 
  mPaint=new Paint(); 
  mPaint.setAntiAlias(true);//消除锯齿 
  mPaint.setColor(paintColor);//画笔颜色 
  mPaint.setAlpha(paintAlph);//画笔透明度 
  mPaint.setStyle(paintStyle);//设置画笔风格 
  mPaint.setStrokeWidth(paintWidth);//设置画笔宽度 
 } 
 public void doDraw(){ 
  mCanvas=surfaceHolder.lockCanvas(); 
  mCanvas.drawPath(mPath, mPaint);//绘制 
  surfaceHolder.unlockCanvasAndPost(mCanvas); 
 }  
 @Override 
 public boolean onTouchEvent(MotionEvent event) { 
  // TODO Auto-generated method stub 
  switch (event.getAction()) { 
  case MotionEvent.ACTION_DOWN: 
   //手接触屏幕时触发 
   doTouchDown(event); 
   break; 
  case MotionEvent.ACTION_MOVE: 
   //手滑动时触发 
   doTouchMove(event); 
   break; 
  case MotionEvent.ACTION_UP: 
   //手抬起时触发 
   break; 
  default: 
   break; 
  } 
  return true; 
 } 
  
 private void doTouchDown(MotionEvent event){ 
  float touchX=event.getX(); 
  float touchY=event.getY(); 
  startX=touchX; 
  startY=touchY; 
  mPath.reset(); 
  mPath.moveTo(touchX, touchY); 
 } 
  
 private void doTouchMove(MotionEvent event){ 
  float touchX=event.getX(); 
  float touchY=event.getY(); 
  float dx=Math.abs(touchX-startX);//移动的距离 
  float dy =Math.abs(touchY-startX);//移动的距离 
  if(dx>3||dy>3){ 
   float cX=(touchX+startX)/2; 
   float cY=(touchY+startY)/2; 
   mPath.quadTo(startX, startY, cX, cY); 
   startX=touchX; 
   startY=touchY; 
  } 
 } 
 public void setPaintColor(int paintColor) { 
  this.paintColor = paintColor; 
  initPaint(); 
 } 
 public void setPaintWidth(float paintWidth) { 
  this.paintWidth = paintWidth; 
  initPaint(); 
 } 
 public void setPaintStyle(Style paintStyle) { 
  this.paintStyle = paintStyle; 
  initPaint(); 
 } 
 public void setPaintAlph(int paintAlph) { 
  this.paintAlph = paintAlph; 
  initPaint(); 
 } 
 @Override 
 public void run() { 
  // TODO Auto-generated method stub 
  while (mIsRunning) { 
    
   long startTime = System.currentTimeMillis(); 
    
   synchronized(surfaceHolder){ 
    doDraw(); 
   } 
    
   long endTime = System.currentTimeMillis(); 
    
   int diffTime = (int) (endTime - startTime); 
    
   while (diffTime <= TIME_IN_FRAME) { 
    diffTime = (int) (System.currentTimeMillis() - startTime); 
     
    Thread.yield(); 
   } 
   } 
 } 
 @Override 
 public void surfaceCreated(SurfaceHolder holder) { 
  // TODO Auto-generated method stub 
  mCanvas =surfaceHolder.lockCanvas(); 
  mCanvas.drawBitmap(bg, 0,0, null); 
  surfaceHolder.unlockCanvasAndPost(mCanvas); 
  mIsRunning=true; 
  new Thread(this).start(); 
 } 
 @Override 
 public void surfaceChanged(SurfaceHolder holder, int format, int width, 
   int height) { 
  // TODO Auto-generated method stub 
 } 
 @Override 
 public void surfaceDestroyed(SurfaceHolder holder) { 
  // TODO Auto-generated method stub 
   mIsRunning = false; 
 } 
} 

看看运行效果：

当我不设置背景时是没问题的，但使用了背景就不停的闪烁了，不知道有没同学知道的，可以说一下。

大家可以阅读本文《解决Android SurfaceView绘制触摸轨迹闪烁问题的方法》，或许对大家的学习有所帮助。

五、总结
两种方式都是可以实现的，而且仔细对比发现surfaceview响应的速度比view快很多，view想必与surfaceview更容易实现。
view用于显示被动更新的动画，即需要操作才会更新的动画，而surfaceview则用于主动更新的动画，如在界面上显示一个奔跑的小狗。
view更新界面是在UI主线程。surfaceview是自己起一个线程更新界面。

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