在Android上开发一些小应用既可以积累知识又可以增加乐趣，与任务式开发不同，所以想到在Android系统上实现一个简单的涂鸦板，这是我们练手 的一种好的方法。
涂鸦板应用的代码实现
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：
<?xmlversion="1.0"encoding="utf-8"?>
<RelativeLayoutxmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
>
<SurfaceView
android:id="@+id/surfaceview"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_above="@+id/line"
android:layout_alignParentTop="true"
/>
<LinearLayout
android:id="@+id/line"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
>
<Button
android:id="@+id/flushbutton"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="清屏"
/>
<Button
android:id="@+id/colorbutton"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="颜色"
/>
</LinearLayout>
</RelativeLayout>
接着，修改MyWallActivity.java文件，最主要是重写了 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。完整的内容如下：
package com.nan.wall;
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;
publicclass MyWallActivity extends Activity
{
private SurfaceView mSurfaceView = null;
private SurfaceHolder mSurfaceHolder = null;
private Button cleanButton = null;
private Button colorButton = null;
privatefloat oldX = 0f;
privatefloat oldY = 0f;
privateboolean canDraw = false;
private Paint mPaint = null;
//用来记录当前是哪一种颜色
privateint whichColor = 0;
/** Called when the activity is first created. */
@Override
publicvoid 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()
{
@Override
publicvoid onClick(View v)
{
// TODO Auto-generated method stub
//锁定整个SurfaceView
Canvas 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()
{
@Override
publicvoid onClick(View v)
{
// TODO Auto-generated method stub
Dialog mDialog = new AlertDialog.Builder(MyWallActivity.this)
.setTitle("颜色设置")
.setSingleChoiceItems(new String[]{"红色","绿色","蓝色"}, whichColor, new DialogInterface.OnClickListener()
{
@Override
publicvoid onClick(DialogInterface dialog, int which)
{
// TODO Auto-generated method stub
switch(which)
{
case0:
{
//画笔的颜色
mPaint.setColor(Color.RED);
whichColor = 0;
break;
}
case1:
{
//画笔的颜色
mPaint.setColor(Color.GREEN);
whichColor = 1;
break;
}
case2:
{
//画笔的颜色106
mPaint.setColor(Color.BLUE);
whichColor = 2;
break;
}
}
}
})
.setPositiveButton("确定", new DialogInterface.OnClickListener()
{
@Override
publicvoid onClick(DialogInterface dialog, int which)
{
// TODO Auto-generated method stub
dialog.dismiss();
}
})
.create();
mDialog.show();
}
});
@Override
publicboolean 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()-50;
//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SurfaceView
Canvas 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;
returntrue;
}
}
应用测试
在模拟器上运行此应用是如下效果：
在Android手机上运行效果则是这样的：
字写的有点丑，但是功能实现了。在获取了Y坐标后减去一个偏移值50，这个值是猜出来的，没 想到在模拟器和真机上定位得都还蛮准的。
应用比较简易，但是大家可以在此基础上丰富它的功能，使其成为一个像样的Android应 用。
