如何在黑莓java的垂直屏幕中对齐图像？

Question

我正在开发一个应用程序，我需要对齐图像，如下所示。

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我尝试下面的代码，但我在屏幕上方获取图像，当我执行下面的代码我做了什么错误请帮助我，我是黑莓新手

public final class MyScreen extends MainScreen
{
private BitmapField bitmapField;

/**
 * Creates a new MyScreen object
 */
public MyScreen()
{        
    // Set the displayed title of the screen       
    setTitle("MyTitle");
    VerticalFieldManager MainLayout = new 
    VerticalFieldManager(Manager.USE_ALL_HEIGHT|Manager.USE_ALL_WIDTH|
  Manager.VERTICAL_SCROLLBAR);
  HorizontalFieldManager hfm =  new      
  HorizontalFieldManager(Field.FIELD_HCENTER | Field.FIELD_VCENTER);
    Bitmap logo1 = Bitmap.getBitmapResource("Lock.png");
    bitmapField = new BitmapField(logo1);
    hfm.add (bitmapField);
    MainLayout.add(hfm);
    add(MainLayout);
}
}