Android 自定义VIEW的运用

---------------------XML

<qianming.co.cc.DrawView
android:id="@+id/draw"
android:layout_width="fill_parent"
android:layout_height="fill_parent" />

-----------------------.java

package qianming.co.cc;

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.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class DrawView extends View {
float preX;
float preY;
private Path path;
public Paint paint = null;
final int VIEW_WIDTH = 1024;
final int VIEW_HEIGHT = 1024;
// 定义一个内存中的图片，该图片将作为缓冲区
Bitmap cacheBitmap = null;
// 定义cacheBitmap上的Canvas对象
Canvas cacheCanvas = null;

public DrawView(Context context, AttributeSet attrs) {
super(context, attrs);
// TODO Auto-generated constructor stub
cacheBitmap = Bitmap.createBitmap(VIEW_WIDTH, VIEW_HEIGHT,
Config.ARGB_8888);
cacheCanvas = new Canvas();
path = new Path();
// 设置cacheCanvas将会绘制到内存中的cacheBitmap上
cacheCanvas.setBitmap(cacheBitmap);
// 设置画笔的颜色
paint = new Paint(Paint.DITHER_FLAG);
paint.setColor(Color.RED);
// 设置画笔风格
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeWidth(4);
// 反锯齿
paint.setAntiAlias(true);
paint.setDither(true);
cacheCanvas.save(Canvas.ALL_SAVE_FLAG );
cacheCanvas.restore();

}

@Override
protected void onDraw(Canvas canvas) {
// TODO Auto-generated method stub
super.onDraw(canvas);
Paint bmpPaint = new Paint();
// 将cacheBitmap绘制到该View组件上
canvas.drawBitmap(cacheBitmap, 0, 0, bmpPaint); // ②
// 沿着path绘制
canvas.drawPath(path, paint);

}

@Override
public boolean onTouchEvent(MotionEvent event) {
// TODO Auto-generated method stub

float x = event.getX();
float y = event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
path.moveTo(x, y);
preX = x;
preY = y;
break;
case MotionEvent.ACTION_MOVE:
path.quadTo(preX, preY, x, y);
preX = x;
preY = y;
break;
case MotionEvent.ACTION_UP:
cacheCanvas.drawPath(path, paint); // ①
path.reset();
break;
}

invalidate();
// 返回true表明处理方法已经处理该事件
return true;
}

}