Question

我的Blackberry应用程序屏幕中有一个背景位图。屏幕已启用滚动，因为我必须有滚动。我面临的问题是，当我向下滚动页面时，背景位图不适合滚动页面，而是显示纯白色背景。我们是否需要为每个滚动页面绘制背景位图？

我的位图大小为：360 * 480

更新的代码是：

class BGVerticalFieldManager extends VerticalFieldManager {
    Bitmap mBgBitmap = null;
    int mBgWidth = -1;
    int mBgHeight = -1;
    int mBgX = -1;
    int mBgY = -1;

    public BGVerticalFieldManager(Bitmap background) {
            super(USE_ALL_WIDTH | USE_ALL_HEIGHT | VERTICAL_SCROLL
                            | VERTICAL_SCROLLBAR);
            mBgBitmap = background;
            mBgWidth = mBgBitmap.getWidth();
            mBgHeight = mBgBitmap.getHeight();
            mBgX = (Display.getWidth() - mBgWidth) >> 1;
            mBgY = (Display.getHeight() - mBgHeight) >> 1;

    }

    protected void paintBackground(Graphics graphics) {
            paintBackgroundBitmap(graphics);
            invalidate();
    }

    /*private void paintBackgroundBitmap(Graphics graphics) {
            if (null != mBgBitmap) {
                    int x = mBgX + ((MainScreen)getScreen())
                        .getMainManager().getHorizontalScroll();
                    int y = mBgY + ((MainScreen)getScreen())
                        .getMainManager().getVerticalScroll();

                    graphics.drawBitmap(x, y, mBgWidth, 
                        mBgHeight, mBgBitmap, 0, 0);
            }
    } */
    private void paintBackgroundBitmap(Graphics graphics) {
    if (null != mBgBitmap) {
        int x = mBgX
                + getHorizontalScroll();
        int y = mBgY
                + getVerticalScroll();
        graphics.drawBitmap(x, y, mBgWidth, mBgHeight, mBgBitmap, 0, 0);
    }
}

}

从下面的另一个文件中调用上面的背景位代码：

public MyFirstScreen ( String label, int screenState, int selectedObj, boolean bUI ) 
{    

   super(VERTICAL_SCROLL | VERTICAL_SCROLLBAR); // I must need it ...

   appTitle = label;
   setTitle(appTitle);

   background = Bitmap.getBitmapResource ("HomeBack.png");        
   add(_container = new BGVerticalFieldManager(background));

   ..............................
   ..............................
   ..............................

}

Answer 1

要获得实际滚动位置，您可以使用getVerticalScroll()：

class BGVerticalFieldManager extends VerticalFieldManager {
    Bitmap mBgBitmap = null;
    int mBgWidth = -1;
    int mBgHeight = -1;
    int mBgX = -1;
    int mBgY = -1;

    public BGVerticalFieldManager(Bitmap background) {
        super(USE_ALL_WIDTH | USE_ALL_HEIGHT | VERTICAL_SCROLL
                | VERTICAL_SCROLLBAR);
        mBgBitmap = background;
        mBgWidth = mBgBitmap.getWidth();
        mBgHeight = mBgBitmap.getHeight();
        mBgX = (Display.getWidth() - mBgWidth) >> 1;
        mBgY = (Display.getHeight() - mBgHeight) >> 1;

    }

    protected void paintBackground(Graphics graphics) {
        paintBackgroundBitmap(graphics);
        invalidate();
    }

    private void paintBackgroundBitmap(Graphics graphics) {
        if (null != mBgBitmap) {
            int x = mBgX
                    + getHorizontalScroll();
            int y = mBgY
                    + getVerticalScroll();
            graphics.drawBitmap(x, y, mBgWidth, mBgHeight, mBgBitmap, 0, 0);
        }
    }
}

alt text http://img693.imageshack.us/img693/6245/9000.jpg
使用样本：

class Scr extends MainScreen {

    private BGVerticalFieldManager mContainer;

    public Scr() {
        super(NO_VERTICAL_SCROLL);
        setTitle("Screen Title");
        Bitmap bitmap = Bitmap.getBitmapResource("BoldOEM.jpg");
        add(mContainer = new BGVerticalFieldManager(bitmap));
        for (int i = 0; i < 100; i++) {
            mContainer.add(new LabelField("List item #" + String.valueOf(i)));
            mContainer.add(new NullField(FOCUSABLE));
        }
    }
}

Answer 2

Max Gontar的回应是电池杀手;

protected void paintBackground(Graphics graphics) {
  paintBackgroundBitmap(graphics);
  invalidate();
}

因为invalidate（）将导致调用paintBackground（Graphics）。

BlackBerry - 背景位图不适合滚动页面

2 个答案: