一、概述
这次要做一个简单的涂鸦板应用，以前在Qt上实现过，突然想到要把它在Android上实现，呵呵，既简单又有趣。
二、实现
新建工程MyWall，修改/res/layout/main.xml文件，在里面添加一个SurfaceView和两个Button，用到了RelativeLayout布局，完整的main.xml文件如下：
1 2 38 9 16 17 23 24 31 32 39 40
接着，修改MyWallActivity.java文件，最主要是覆写了onTouchEvent（）函数，在这个函数里过滤出触屏拖动事件，然后获取其相应的坐标和画线，关于SurfaceView的用法在基础篇里有讲到。完整的内容如下：
1 package com.nan.wall; 2 3 import android.app.Activity; 4 import android.app.AlertDialog; 5 import android.app.Dialog; 6 import android.content.DialogInterface; 7 import android.graphics.Canvas; 8 import android.graphics.Color; 9 import android.graphics.Paint; 10 import android.graphics.Rect; 11 import android.os.Bundle; 12 import android.view.MotionEvent; 13 import android.view.SurfaceHolder; 14 import android.view.SurfaceView; 15 import android.view.View; 16 import android.widget.Button; 17 18 public class MyWallActivity extends Activity 19 { 20 private SurfaceView mSurfaceView = null; 21 private SurfaceHolder mSurfaceHolder = null; 22 private Button cleanButton = null; 23 private Button colorButton = null; 24 25 private float oldX = 0f; 26 private float oldY = 0f; 27 28 private boolean canDraw = false; 29 private Paint mPaint = null; 30 //用来记录当前是哪一种颜色 31 private int whichColor = 0; 32 33 /** Called when the activity is first created. */ 34 @Override 35 public void onCreate(Bundle savedInstanceState) 36 { 37 super.onCreate(savedInstanceState); 38 setContentView(R.layout.main); 39 40 mSurfaceView = (SurfaceView)this.findViewById(R.id.surfaceview); 41 mSurfaceHolder = mSurfaceView.getHolder(); 42 43 mPaint = new Paint(); 44 //画笔的颜色 45 mPaint.setColor(Color.RED); 46 //画笔的粗细 47 mPaint.setStrokeWidth(2.0f); 48 49 cleanButton = (Button)this.findViewById(R.id.flushbutton); 50 //按钮监听 51 cleanButton.setOnClickListener(new View.OnClickListener() 52 { 53 54 @Override 55 public void onClick(View v) 56 { 57 // TODO Auto-generated method stub 58 //锁定整个SurfaceView 59 Canvas mCanvas = mSurfaceHolder.lockCanvas(); 60 mCanvas.drawColor(Color.BLACK); 61 //绘制完成，提交修改 62 mSurfaceHolder.unlockCanvasAndPost(mCanvas); 63 //重新锁一次 64 mSurfaceHolder.lockCanvas(new Rect(0, 0, 0, 0)); 65 mSurfaceHolder.unlockCanvasAndPost(mCanvas); 66 } 67 }); 68 69 colorButton = (Button)this.findViewById(R.id.colorbutton); 70 //按钮监听 71 colorButton.setOnClickListener(new View.OnClickListener() 72 { 73 74 @Override 75 public void onClick(View v) 76 { 77 // TODO Auto-generated method stub 78 Dialog mDialog = new AlertDialog.Builder(MyWallActivity.this) 79 .setTitle("颜色设置") 80 .setSingleChoiceItems(new String[]{"红色","绿色","蓝色"}, whichColor, new DialogInterface.OnClickListener() 81 { 82 83 @Override 84 public void onClick(DialogInterface dialog, int which) 85 { 86 // TODO Auto-generated method stub 87 switch(which) 88 { 89 case 0: 90 { 91 //画笔的颜色 92 mPaint.setColor(Color.RED); 93 whichColor = 0; 94 break; 95 } 96 case 1: 97 { 98 //画笔的颜色 99 mPaint.setColor(Color.GREEN); 100 whichColor = 1; 101 break; 102 } 103 case 2: 104 { 105 //画笔的颜色 106 mPaint.setColor(Color.BLUE); 107 whichColor = 2; 108 break; 109 } 110 } 111 } 112 }) 113 .setPositiveButton("确定", new DialogInterface.OnClickListener() 114 { 115 116 @Override 117 public void onClick(DialogInterface dialog, int which) 118 { 119 // TODO Auto-generated method stub 120 dialog.dismiss(); 121 } 122 }) 123 .create(); 124 mDialog.show(); 125 } 126 }); 127 128 } 129 130 131 @Override 132 public boolean onTouchEvent(MotionEvent event) 133 { 134 //获取x坐标 135 float x = event.getX(); 136 //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） 137 float y = event.getY()-50; 138 139 //第一次进来先不管 140 if(canDraw) 141 { 142 //获取触屏事件 143 switch(event.getAction()) 144 { 145 //如果是拖动事件 146 case MotionEvent.ACTION_MOVE: 147 { 148 149 //锁定整个SurfaceView 150 Canvas mCanvas = mSurfaceHolder.lockCanvas(); 151 mCanvas.drawLine(x, y, oldX, oldY, mPaint); 152 mSurfaceHolder.unlockCanvasAndPost(mCanvas); 153 //重新锁一次 154 mSurfaceHolder.lockCanvas(new Rect(0, 0, 0, 0)); 155 mSurfaceHolder.unlockCanvasAndPost(mCanvas); 156 break; 157 } 158 } 159 160 } 161 //保存目前的x坐标值 162 oldX = x; 163 //保存目前的y坐标值 164 oldY = y; 165 166 canDraw = true; 167 168 return true; 169 } 170 171 } 好了，在模拟器上运行效果如下：
在真机上运行效果如下：
呵呵，写得比较丑。
在获取了Y坐标后减去一个偏移值50，这个值是我直接猜出来的，没想到在模拟器和真机上定位得还蛮准的，哈哈。当然这个应用的功能不多，不过有兴趣的话可以再完善它，希望能起到抛砖引玉的作用。