自定义ViewGroup焦点处理 [英] Custom ViewGroup focus handling

问题描述

假设我有一个自定义的ViewGroup，这个ViewGroup是可调焦的，并且有一些子视图也是可以调焦的（一个自定义的Android机顶盒的垂直菜单，它应该在遥控器上做出反应）。

每当自定义ViewGroup获得焦点时，我需要将焦点传递给一些子视图。

我将 descendantFocusability 设置为 beforeDescendants 并将 OnFocusChangeListener ViewGroup但永远不会调用 OnFocusChangeListener.onFocusChanged（）。它看起来像 beforeDescendants 不能按我的预期工作。实际上，设置 beforeDescendants 与设置 afterDescendants 相同 - 焦点由最近的子视图和自定义ViewGroup没有机会决定哪个子视图需要关注。

我该如何达到所需的行为？什么是处理焦点在 ViewGroup s？

解决方案

在Android资源挖掘后，我知道如何派遣焦点到 ViewGroup 的孩子。例如，我在里面定制了 ViewGroup ，里面没有 EditText 字段。当用户点击 ViewGroup （每个 EditText 之外）时，我想把焦点调度到一个字段。 p>

为此，我们需要将descendantFocusability设置为 FOCUS_AFTER_DESCENDANTS 。这意味着我们可以在之前处理焦点事件，我们的自定义视图将尝试着重于自己：

  setDescendantFocusability （FOCUS_AFTER_DESCENDANTS）; 
  

下一步是重写 onRequestFocusInDescendants 方法，它将在自定义视图的 requestFocus 之前被调用 FOCUS_AFTER_DESCENDANTS 被设置。在这个方法中，我们可以请求关注子对象：

$ @ $ $
保护布尔onRequestFocusInDescendants（final int dir，final Rect rect ）{
return getChildAt（this.target）.requestFocus（）;



$ b $ p
$ b

这个方法的一个重要的事情是：如果我们返回真正的在这里，我们的自定义视图将不会被要求重点（只有 FOCUS_AFTER_DESCENDANTS ）。

通过这种方式，当点击 ViewGroup 时，我们可以改变 target 字段来改变哪个孩子会被关注。

$ h
为了更好地理解，可以在 requestFocus 方法> ViewGroup 在Android来源。

Let's say I have a custom ViewGroup which is focusable and has some child views which are focusable as well (A custom vertical menu for Android set-top-boxes which should react on remote controller).

I need to pass a focus to some of the child views whenever the custom ViewGroup gains the focus.

I set descendantFocusability to beforeDescendants and set OnFocusChangeListener to the custom ViewGroup but OnFocusChangeListener.onFocusChanged()is never called. It looks like beforeDescendants does not work as I expected. Actually setting the beforeDescendants works the same as setting the afterDescendants - The focus is taken by the nearest child view and the custom ViewGroup does not have an opportunity to decide which child view should take the focus.

How can I achieve the desired behavior? What are the best practices to handling focuses in ViewGroups?

解决方案

After digging in Android sources I understand how to dispatch focus to ViewGroup's children. For example I have custom ViewGroup with few EditText fields inside. When the user clicks on ViewGroup (outside of each EditText) I want to dispatch focus to one of fields.

To do this we need to set descendantFocusability to FOCUS_AFTER_DESCENDANTS. It means that we can handle focus event before our custom view will try to focus itself:

setDescendantFocusability(FOCUS_AFTER_DESCENDANTS);

Next step is to override onRequestFocusInDescendants method, it will be invoked before custom view's requestFocus if flag FOCUS_AFTER_DESCENDANTS was set. In this method we can request child focus:

@Override
protected boolean onRequestFocusInDescendants(final int dir, final Rect rect) {
    return getChildAt(this.target).requestFocus();
}

One important thing with this method: if we return true here, our custom view will not be requested to focus (only with FOCUS_AFTER_DESCENDANTS).

In such a manner we can change target field to change which child will be focused when ViewGroup is clicked.

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For better understanding you can find requestFocus method in ViewGroup in Android sources.

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