blackberry - labelField.getWidth() 返回 0？为什么会这样？

Question

我正在开发我自己的自定义管理器，到目前为止我已经完成了它，但是它使用屏幕分辨率的百分比来设置边距。

下面是我如何调用下面的类:

LabelIconCommandManager licm3 = new LabelIconCommandManager("Address blah bklahblah ", 0);
licm3.add(new ImageButtonField(b1, b2, b3, Field.FIELD_LEFT | ImageButtonField.CONSUME_CLICK));

这是类 [我在评论中标记了返回 0 和返回 219 的地方。请告诉我为什么会这样:

public class LabelIconCommandManager extends HorizontalFieldManager implements  BCMSField
{
    LabelIconCommandManager me = this;
    EvenlySpacedHorizontalFieldManager buttonManager = new EvenlySpacedHorizontalFieldManager(0);
    LabelField labelField;
    int side = 0;
    int HPADDING = 3;
    int VPADDING = 4;
    int screenWidth = Display.getWidth();
    int labelField_width = 40;
    public LabelIconCommandManager()
    {
        this("", 0);
    }
    public LabelIconCommandManager(String label, long style)
    {
        super(USE_ALL_WIDTH| FOCUSABLE);
        this.setBorder(BorderFactory.createBitmapBorder(new XYEdges(15, 20, 15, 20),Bitmap.getBitmapResource( "border_edit.png" )));
        this.setMargin(1,10,1,10);
        labelField = new LabelField(label,LabelField.ELLIPSIS)
        {
            public void layout(int width, int height)
            {
                // Done because otherwise ellipses dont work with labelfields
                super.layout((int)(screenWidth * 0.61), getHeight());
                setExtent((int)(screenWidth * 0.61), getHeight());
                labelField_width = labelField.getWidth();
                DisplayDialog.alert("labelField_width = " + labelField_width); // returns 219
            }
        };
        // Top Right Bottom Left
        labelField.setMargin(VPADDING, HPADDING, VPADDING, 0);
        // super because we want this horizontalfieldManager to add it
        super.add(labelField);
        super.add(buttonManager);
    }
    public void alternateConstructor(Attributes atts)
    {
        labelField = new LabelField(atts.getValue("label"), 0);
    }
    public void onFocus(int direction)
    {
        this.setBorder(BorderFactory.createBitmapBorder(new XYEdges(15, 20, 15, 20),Bitmap.getBitmapResource( "border_edit_select.png" )));
        // uses the same color as listStyleButtonField selections
        this.setBackground(BackgroundFactory.createSolidBackground(0x186DEF));
        super.onFocus(direction);
    }
    //Invoked when a field loses the focus.
    public void onUnfocus()
    {
        //top, right,bottom,left
        this.setBorder(BorderFactory.createBitmapBorder(new XYEdges(15, 20, 15, 20),Bitmap.getBitmapResource( "border_edit.png" )));
        this.setBackground(BackgroundFactory.createSolidTransparentBackground(Color.GRAY, 0));
        super.onUnfocus();
        invalidate();
    }
    // Overrride this managers add function
    public void add(Field imageButton)
    {
        // Add a button to the evenly spaced manager
        buttonManager.add(imageButton);
        // Based on how many buttons there are, set the margin of where the manager holding the buttons start [offset from labelField]
        if(buttonManager.getFieldCount() == 1)
        {
            //side = (int)(screenWidth * 0.1388);
            side = screenWidth - labelField_width - 32 - 10 - 15;
            DisplayDialog.alert("Screen Width = " + screenWidth);
            DisplayDialog.alert("labelField_width2 = " + labelField_width); // returns 0
            DisplayDialog.alert("Side = " + side);
        }
        else side = (int)(screenWidth * 0.05);
        buttonManager.setMargin(0,0,0,side);
    }
    public int getLabelWidth()
    {
        return labelField_width;
    }
}  

为了更清楚，这里有一张图片:

Answer 1

注意:当我运行您的代码时，我实际上并没有看到 labelField_width 设置为 0。您在上面发布的代码中将该值初始化为 40。因此，我有时会看到它设置为 40 或 219(在 360 像素宽的屏幕上)。

但是，问题是我认为您过早地试图访问 labelField_width 的值。它唯一正确分配的位置是在匿名 LabelField 的 layout() 方法中。仅仅因为您根据实例化声明并实现了 layout() 方法，并不意味着它在创建 LabelField 时被调用。这其实也是我不喜欢匿名类的原因之一。

无论如何，这段代码:

LabelIconCommandManager licm3 = new LabelIconCommandManager("Address blah bklahblah ", 0); 
licm3.add(new ImageButtonField(b1, b2, b3, Field.FIELD_LEFT | ImageButtonField.CONSUME_CLICK));

将首先实例化 LabelField(在 LabelIconCommandManager 构造函数内)。正如我所说，这不会触发layout() 方法。上面的第二行 (add()) 将触发您重写的方法:

// Overrride this managers add function 
public void add(Field imageButton) 
{ 

这是您看到 labelField_width 错误值的地方。该方法在 layout() 之前被调用。这就是问题所在。

因为看起来您只使用该宽度来设置 buttonManager 边距，所以您可以稍等片刻。如果您等到 LabelIconCommandManager sublayout() 方法被调用，您的 LabelField 将有其 layout()调用方法，并正确分配 labelField_width:

protected void sublayout(int maxWidth, int maxHeight) {
   // make sure to call superclass method first!
   super.sublayout(maxWidth, maxHeight);

   // now, we can reliably use the label width:
   side = screenWidth - labelField_width - 32 - 10 - 15; 
   buttonManager.setMargin(0,0,0,side); 
}

该方法位于 LabelIconCommandManager 类中。然后，您可以删除调用 buttonManager.setMargin() 的其他地方。