android中图片翻页效果简单的实现方法

public class pagewidget extends view {
    private bitmap foreimage;
    private bitmap bgimage;
    private pointf touchpt;
    private int screenwidth;
    private int screenheight;
    private gradientdrawable shadowdrawablerl;
    private gradientdrawable shadowdrawablelr;
    private colormatrixcolorfilter mcolormatrixfilter;
    private scroller mscroller;
    private int lasttouchx;

    public pagewidget(context context) {
        super(context);
        // todo auto-generated constructor stub
        touchpt = new pointf(-1,-1);

        //argb a(0-透明,255-不透明)
        int[] color = { 0xb0333333 ,0x00333333};
        shadowdrawablerl = new gradientdrawable(gradientdrawable.orientation.right_left, color);
        shadowdrawablerl.setgradienttype(gradientdrawable.linear_gradient);

        shadowdrawablelr = new gradientdrawable(gradientdrawable.orientation.left_right, color);
        shadowdrawablelr.setgradienttype(gradientdrawable.linear_gradient);

         float array[] = { 0.55f,    0,    0,     0, 80.0f,
    ,0.55f,    0,     0, 80.0f,
    ,    0,0.55f,     0, 80.0f,
    ,    0,    0,  0.2f, 0};
        colormatrix cm = new colormatrix();
        cm.set(array);
        /*
         * |a*0.55 + 80|
         * |r*0.55 + 80|
         * |g*0.55 + 80|
         * |b*0.2|
         */
//      cm.setsaturation(0);
        mcolormatrixfilter = new colormatrixcolorfilter(cm);

        //利用滚动条来实现接触点放开后的动画效果
        mscroller = new scroller(context);
    }

    @override
    public void computescroll() {
        // todo auto-generated method stub
        if (mscroller.computescrolloffset()) {
            touchpt.x = mscroller.getcurrx();
            touchpt.y = mscroller.getcurry();

            postinvalidate();
        }
        else{
//            touchpt.x = -1;
//            touchpt.y = -1;           
        }

        super.computescroll();
    }

    public void setscreen(int screenwidth,int screenheight){
        this.screenwidth = screenwidth;
        this.screenheight = screenheight;
    }

    public bitmap getforeimage() {
        return foreimage;
    }

    public void setforeimage(bitmap foreimage) {
        this.foreimage = foreimage;
    }

    public bitmap getbgimage() {
        return bgimage;
    }

    public void setbgimage(bitmap bgimage) {
        this.bgimage = bgimage;
    }

    @override
    protected void ondraw(canvas canvas) {
        // todo auto-generated method stub
        drawpageeffect(canvas);
        super.ondraw(canvas);
    }

    /**
     * 画前景图片
     * @param canvas
     */
    private void drawforceimage(canvas canvas) {
        // todo auto-generated method stub
        paint mpaint = new paint();

        if (foreimage!=null) {
            canvas.drawbitmap(foreimage, 0, 0, mpaint);
        }       
    }

    /**
     * 画背景图片
     * @param canvas
     */
    private void drawbgimage(canvas canvas,path path) {
        // todo auto-generated method stub
        paint mpaint = new paint();

        if (bgimage!=null) {
            canvas.save();

            //只在与路径相交处画图
            canvas.clippath(path,op.intersect);
            canvas.drawbitmap(bgimage, 0, 0, mpaint);
            canvas.restore();
        }
    }

    /**
     * 画翻页效果
     * @param canvas
     */
    private void drawpageeffect(canvas canvas) {
        // todo auto-generated method stub
        drawforceimage(canvas);
        paint mpaint = new paint();
        if (touchpt.x!=-1 && touchpt.y!=-1) {
            //翻页左侧书边
            canvas.drawline(touchpt.x, 0, touchpt.x,screenheight, mpaint);

            //左侧书边画阴影
            shadowdrawablerl.setbounds((int)touchpt.x - 20, 0 ,(int)touchpt.x, screenheight);
            shadowdrawablerl.draw(canvas);

            //翻页对折处
            float halfcut = touchpt.x + (screenwidth - touchpt.x)/2;
            canvas.drawline(halfcut, 0, halfcut, screenheight, mpaint);

            //对折处左侧画翻页页图片背面
            rect backarea = new rect((int)touchpt.x,0,(int)halfcut,screenheight);
            paint backpaint = new paint();
            backpaint.setcolor(0xffdacab0);
            canvas.drawrect(backarea, backpaint);

            //将翻页图片正面进行处理水平翻转并平移到touchpt.x点
            paint fbpaint = new paint();
            fbpaint.setcolorfilter(mcolormatrixfilter);
            matrix matrix = new matrix();

            matrix.prescale(-1,1);
            matrix.posttranslate(foreimage.getwidth() + touchpt.x,0);

            canvas.save();
            canvas.cliprect(backarea);
            canvas.drawbitmap(foreimage, matrix, fbpaint);
            canvas.restore();

            //对折处画左侧阴影
            shadowdrawablerl.setbounds((int)halfcut - 50, 0 ,(int)halfcut, screenheight);
            shadowdrawablerl.draw(canvas);

            path bgpath = new path();

            //可以显示背景图的区域
            bgpath.addrect(new rectf(halfcut,0,screenwidth,screenheight), direction.cw);

            //对折出右侧画背景
            drawbgimage(canvas,bgpath);

            //对折处画右侧阴影
            shadowdrawablelr.setbounds((int)halfcut, 0 ,(int)halfcut + 50, screenheight);
            shadowdrawablelr.draw(canvas);
        }
    }

    @override
    public boolean ontouchevent(motionevent event) {
        // todo auto-generated method stub
        if (event.getaction() == motionevent.action_down) {
            touchpt.x = event.getx();
            touchpt.y =    event.gety();
        }
        else if(event.getaction() == motionevent.action_move){
            lasttouchx = (int)touchpt.x;
            touchpt.x = event.getx();
            touchpt.y =    event.gety();

            postinvalidate();
        }
        else if(event.getaction() == motionevent.action_up){
            int dx,dy;

            dy = 0;

            //向右滑动
            if (lasttouchx<touchpt.x) {
                dx = foreimage.getwidth() - (int)touchpt.x + 30;
            }
            else{
            //向左滑动
                dx = -(int)touchpt.x - foreimage.getwidth();
            }

            mscroller.startscroll((int)touchpt.x,(int)touchpt.y,dx,dy,1000);
            postinvalidate();
        }

        //必须为true，否则无法获取action_move及action_up事件
        return true;
    }
}

public class pageactivity extends activity {
    protected void oncreate(android.os.bundle savedinstancestate) {
        requestwindowfeature(window.feature_no_title);

        pagewidget pagewidget = new pagewidget(this);

        display display = getwindowmanager().getdefaultdisplay();
        int width  = display.getwidth();
        int height = display.getheight();

        pagewidget.setscreen(width, height);

        bitmap bm1 = bitmapfactory.decoderesource(getresources(), r.drawable.pre7);
        bitmap bm2 = bitmapfactory.decoderesource(getresources(), r.drawable.after7);

        bitmap foreimage = bitmap.createscaledbitmap(bm1, width, height,false);
        bitmap bgimage = bitmap.createscaledbitmap(bm2, width, height,false);

        pagewidget.setbgimage(bgimage);
        pagewidget.setforeimage(foreimage);

        setcontentview(pagewidget);

        super.oncreate(savedinstancestate);
    };
}