修改后的代码[1]为，少了一个}

package com.example.administrator.myapplication;import android.app.Activity;
import android.app.AlertDialog;
import android.app.Dialog;
import android.content.DialogInterface;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
import android.widget.Button;public class MyWallActivity extends Activity
{private SurfaceView mSurfaceView = null;private SurfaceHolder mSurfaceHolder = null;private Button cleanButton = null;private Button colorButton = null;private float oldX = 0f;private float oldY = 0f;private boolean canDraw = false;private Paint mPaint = null;//用来记录当前是哪一种颜色private int whichColor = 0;/** Called when the activity is first created. */@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);mSurfaceView = (SurfaceView) this.findViewById(R.id.surfaceview);mSurfaceHolder = mSurfaceView.getHolder();mPaint = new Paint();
//画笔的颜色mPaint.setColor(Color.RED);
//画笔的粗细mPaint.setStrokeWidth(2.0f);cleanButton = (Button) this.findViewById(R.id.flushbutton);
//按钮监听cleanButton.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {
// TODO Auto-generated method stub
//锁定整个SurfaceViewCanvas mCanvas = mSurfaceHolder.lockCanvas();mCanvas.drawColor(Color.BLACK);
//绘制完成，提交修改mSurfaceHolder.unlockCanvasAndPost(mCanvas);
//重新锁一次mSurfaceHolder.lockCanvas(new Rect(0, 0, 0, 0));mSurfaceHolder.unlockCanvasAndPost(mCanvas);}});colorButton = (Button) this.findViewById(R.id.colorbutton);
//按钮监听colorButton.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubDialog mDialog = new AlertDialog.Builder(MyWallActivity.this).setTitle("corlor setting").setSingleChoiceItems(new String[]{"red", "green", "blue"}, whichColor, new DialogInterface.OnClickListener() {@Overridepublic void onClick(DialogInterface dialog, int which) {// TODO Auto-generated method stubswitch (which) {case 0: {
//画笔的颜色mPaint.setColor(Color.RED);whichColor = 0;break;}case 1: {
//画笔的颜色mPaint.setColor(Color.GREEN);whichColor = 1;break;}case 2: {
//画笔的颜色106mPaint.setColor(Color.BLUE);whichColor = 2;break;}}}}).setPositiveButton("confirm", new DialogInterface.OnClickListener() {@Overridepublic void onClick(DialogInterface dialog, int which) {
// TODO Auto-generated method stubdialog.dismiss();}}).create();mDialog.show();}});}@Overridepublic boolean onTouchEvent(MotionEvent event){
//获取x坐标float x = event.getX();
//获取y坐标（不知道为什么要减去一个偏移值才对得准屏幕）float y = event.getY();
//第一次进来先不管if(canDraw){
//获取触屏事件switch(event.getAction()){
//如果是拖动事件case MotionEvent.ACTION_MOVE:{
//锁定整个SurfaceViewCanvas mCanvas = mSurfaceHolder.lockCanvas();mCanvas.drawLine(x, y, oldX, oldY, mPaint);mSurfaceHolder.unlockCanvasAndPost(mCanvas);
//重新锁一次mSurfaceHolder.lockCanvas(new Rect(0, 0, 0, 0));mSurfaceHolder.unlockCanvasAndPost(mCanvas);break;}}}
//保存目前的x坐标值oldX = x;
//保存目前的y坐标值oldY = y;canDraw = true;return true;}}

[2]里面有个demo可以直接使用，应该是eclipse上的，我转换为了as的，不过有锯齿

[3]使用贝塞尔曲线的方法去除了锯齿

在[4]中可以使用橡皮擦，貌似需要更改一些东西，否则会闪退，可能和用的是as相关

package com.example.administrator.myapplication;import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.os.Bundle;
import android.util.DisplayMetrics;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup.LayoutParams;
import android.widget.Button;
import android.widget.LinearLayout;public class MainActivity extends Activity {private int SCREEN_W;private int SCREEN_H;private int Pen = 1;private int Eraser = 2;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);LinearLayout layout = new LinearLayout(this);layout.setOrientation(LinearLayout.VERTICAL);LayoutParams params = new LayoutParams(LayoutParams.WRAP_CONTENT,LayoutParams.WRAP_CONTENT);Button paint = new Button(this);paint.setText("画笔");layout.addView(paint, params);Button eraser = new Button(this);eraser.setText("橡皮");layout.addView(eraser, params);final MyView myView = new MyView(this);layout.addView(myView);setContentView(layout);paint.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {myView.setMode(Pen);}});eraser.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {myView.setMode(Eraser);}});}//MyView就是自定义的画板class MyView extends View {private int mMode = 1;private Bitmap mBitmap;private Canvas mCanvas;private Paint mEraserPaint;private Paint mPaint;private Path mPath;private float mX, mY;private static final float TOUCH_TOLERANCE = 4;public MyView(Context context) {super(context);setFocusable(true);setScreenWH();initPaint();}private void setScreenWH() {DisplayMetrics dm = new DisplayMetrics();dm = this.getResources().getDisplayMetrics();int screenWidth = dm.widthPixels;int screenHeight = dm.heightPixels;SCREEN_W = screenWidth;SCREEN_H = screenHeight;}//设置绘制模式是“画笔”还是“橡皮擦”public void setMode(int mode){this.mMode = mode;}private void initPaint() {//画笔mPaint = new Paint();mPaint.setAntiAlias(true);mPaint.setStyle(Paint.Style.STROKE);mPaint.setStrokeCap(Paint.Cap.ROUND);mPaint.setStrokeJoin(Paint.Join.ROUND);mPaint.setColor(Color.BLACK);mPaint.setStrokeWidth(10);//橡皮擦mEraserPaint = new Paint();mEraserPaint.setAlpha(0);//这个属性是设置paint为橡皮擦重中之重//这是重点//下面这句代码是橡皮擦设置的重点mEraserPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));//上面这句代码是橡皮擦设置的重点（重要的事是不是一定要说三遍）mEraserPaint.setAntiAlias(true);mEraserPaint.setDither(true);mEraserPaint.setStyle(Paint.Style.STROKE);mEraserPaint.setStrokeJoin(Paint.Join.ROUND);mEraserPaint.setStrokeWidth(30);mPath = new Path();mBitmap = Bitmap.createBitmap(SCREEN_W, SCREEN_H, Config.ARGB_8888);mCanvas = new Canvas(mBitmap);}@Overrideprotected void onDraw(Canvas canvas) {if (mBitmap != null) {canvas.drawBitmap(mBitmap, 0, 0, mPaint);}super.onDraw(canvas);}private void touch_start(float x, float y) {mPath.reset();mPath.moveTo(x, y);mX = x;mY = y;//如果是“画笔”模式就用mPaint画笔进行绘制if (mMode == Pen) {mCanvas.drawPath(mPath, mPaint);}//如果是“橡皮擦”模式就用mEraserPaint画笔进行绘制if (mMode == Eraser) {mCanvas.drawPath(mPath, mEraserPaint);}}private void touch_move(float x, float y) {float dx = Math.abs(x - mX);float dy = Math.abs(y - mY);if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {mPath.quadTo(mX, mY, (x + mX) / 2, (y + mY) / 2);mX = x;mY = y;if (mMode == Pen) {mCanvas.drawPath(mPath, mPaint);}if (mMode == Eraser) {mCanvas.drawPath(mPath, mEraserPaint);}}}private void touch_up() {mPath.lineTo(mX, mY);if (mMode == Pen) {mCanvas.drawPath(mPath, mPaint);}if (mMode == Eraser) {mCanvas.drawPath(mPath, mEraserPaint);}}@Overridepublic boolean onTouchEvent(MotionEvent event) {float x = event.getX();float y = event.getY();switch (event.getAction()) {case MotionEvent.ACTION_DOWN:touch_start(x, y);invalidate();break;case MotionEvent.ACTION_MOVE:touch_move(x, y);invalidate();break;case MotionEvent.ACTION_UP:touch_up();invalidate();break;}return true;}}
}

[1] 一个简单涂鸦http://www.jizhuomi.com/android/example/19.html

[2] 安卓实现代码的多种方式

[3] 安卓path类的lineTo和quadTo方法的区别

[4] 带画板http://www.mamicode.com/info-detail-1480421.html