requestFocus() 与 requestFocusFromTouch() 方法的区别

最新推荐文章于 2023-11-17 10:14:46 发布

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本文探讨了Android中requestFocus()和requestFocusFromTouch()的区别。requestFocus()用于常规获取焦点，而requestFocusFromTouch()则在触摸事件发生时请求焦点。了解这两个方法的工作原理对于优化用户交互至关重要。

两个方法都是获取焦点：

requestFocus() 源码如下：

/**
     * Call this to try to give focus to a specific view or to one of its descendants
     * and give it hints about the direction and a specific rectangle that the focus
     * is coming from.  The rectangle can help give larger views a finer grained hint
     * about where focus is coming from, and therefore, where to show selection, or
     * forward focus change internally.
     *
     * @return Whether this view or one of its descendants actually took focus.
     */
    public boolean requestFocus(int direction, Rect previouslyFocusedRect) {
        // need to be focusable
        if ((mViewFlags & FOCUSABLE_MASK) != FOCUSABLE ||
                (mViewFlags & VISIBILITY_MASK) != VISIBLE) {
            return false;
        }


        // need to be focusable in touch mode if in touch mode
        if (isInTouchMode() &&
            (FOCUSABLE_IN_TOUCH_MODE != (mViewFlags & FOCUSABLE_IN_TOUCH_MODE))) {
               return false;
        }


        // need to not have any parents blocking us
        if (hasAncestorThatBlocksDescendantFocus()) {
            return false;
        }


        handleFocusGainInternal(direction, previouslyFocusedRect);
        return true;
    }

requestFocusFromTouch() 源码如下：

 /**
     * Call this to try to give focus to a specific view or to one of its descendants. This is a
     * special variant of {@link #requestFocus() } that will allow views that are not focuable in
     * touch mode to request focus when they are touched.
     *
     * @return Whether this view or one of its descendants actually took focus.
     *
     * @see #isInTouchMode()
     *
     */
    public final boolean requestFocusFromTouch() {
        // Leave touch mode if we need to
        if (isInTouchMode()) {
            ViewRootImpl viewRoot = getViewRootImpl();
            if (viewRoot != null) {
                viewRoot.ensureTouchMode(false);
            }
        }
        return requestFocus(View.FOCUS_DOWN);
    }

从代码中可以看出：
requestFocus() 方法在三种情况下获取焦点不能生效。
1）对应的View不支持Focus;
2) 对应的View支持Focus，但是不支持在Touch模式下的Focus;
3) 对应的View其祖先View 设置了FOCUS_BLOCK_DESCENDANTS 标志，阻止其子View获取焦点。

而requestFocusFromTouch() 方法设计的目的就是解决requestFocus() 在第二种不能获得焦点的情况下，Touch模式下不支持焦点，也能够获得焦点使用的。