Blackberry ButtonField的可見性取決於LabelField焦點

Question

我在我的UI 2按鈕中有3個字段，其中一個位於標籤字段的頂部和其他位置...當標籤字段獲得焦點時，我希望按鈕出現，而我應該能夠點擊他們...當標籤領域失去焦點時，按鈕應該消失..如何才能做到這一點...

Answer 1

把一些經理字段作爲佔位符在按鈕位置，然後添加一個FocusChangeListener在focusChanged上標記和使用add/delete字段以顯示/隱藏按鈕。

UPDATE
因爲從領域的每一個重點的變化可能會改變佈局，認爲它能夠更好地監聽器添加到每個字段添加到屏幕和佔位符：

class Scr extends MainScreen { 
    HorizontalFieldManager placeholder = new HorizontalFieldManager() { 
     public void add(Field field) { 
      if (field.getFocusListener() != null) 
       field.setFocusListener(null); 
      field.setFocusListener(focusListener); 
      super.add(field); 
     } 
    }; 
    ButtonField buttonField = new ButtonField("button", 
      ButtonField.CONSUME_CLICK); 
    LabelField labelField = new LabelField("label", FOCUSABLE); 

    public Scr() { 
     add(placeholder); 
     add(labelField); 
     add(new LabelField("label2", FOCUSABLE)); 
    } 

    public void add(Field field) { 
     if (!(field instanceof Manager)) { 
      if (field.getFocusListener() != null) 
       field.setFocusListener(null); 
      field.setFocusListener(focusListener); 
     } 
     super.add(field); 
    } 

    FocusChangeListener focusListener = new FocusChangeListener() { 
     public void focusChanged(Field field, int eventType) { 
      if (eventType == FOCUS_GAINED) { 
       if (field == labelField) { 
        if (buttonField.getManager() == null) 
         placeholder.add(buttonField); 
       } else if (field != buttonField) 
        placeholder.delete(buttonField); 
      } 
     } 
    }; 
}