Android子view的pressed状态受父view的clickable影响分析

android从sdk16开始，修改了onTouchEvent的ACTION_DOWN代码(Android: Child elements sharing pressed state with their parent even when duplicateParentState specified)，如下：

sdk16以前：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25

case MotionEvent.ACTION_DOWN:
            mHasPerformedLongPress = false;

            if (performButtonActionOnTouchDown(event)) {
                break;
            }

            // Walk up the hierarchy to determine if we're inside a scrolling container.
            boolean isInScrollingContainer = isInScrollingContainer();

            // For views inside a scrolling container, delay the pressed feedback for
            // a short period in case this is a scroll.
            if (isInScrollingContainer) {
                mPrivateFlags |= PREPRESSED;
                if (mPendingCheckForTap == null) {
                    mPendingCheckForTap = new CheckForTap();
                }
                postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
            } else {
                // Not inside a scrolling container, so show the feedback right away
                mPrivateFlags |= PRESSED; //comment by bran
                refreshDrawableState();
                checkForLongClick(0);
            }
            break;

sdk16及以后：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

case MotionEvent.ACTION_DOWN:
            mHasPerformedLongPress = false;

            if (performButtonActionOnTouchDown(event)) {
                break;
            }

            // Walk up the hierarchy to determine if we're inside a scrolling container.
            boolean isInScrollingContainer = isInScrollingContainer();

            // For views inside a scrolling container, delay the pressed feedback for
            // a short period in case this is a scroll.
            if (isInScrollingContainer) {
                mPrivateFlags |= PFLAG_PREPRESSED;
                if (mPendingCheckForTap == null) {
                    mPendingCheckForTap = new CheckForTap();
                }
                postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
            } else {
                // Not inside a scrolling container, so show the feedback right away
                setPressed(true);
                checkForLongClick(0);
            }
            break;

后者会调用setPressed方法，代码如下：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29

    public void setPressed(boolean pressed) {
        final boolean needsRefresh = pressed != ((mPrivateFlags & PFLAG_PRESSED) == PFLAG_PRESSED);

        if (pressed) {
            mPrivateFlags |= PFLAG_PRESSED;
        } else {
            mPrivateFlags &= ~PFLAG_PRESSED;
        }

        if (needsRefresh) {
            refreshDrawableState();
        }
        dispatchSetPressed(pressed);
    }

    //viewgroup的实现
    protected void dispatchSetPressed(boolean pressed) {
        final View[] children = mChildren;
        final int count = mChildrenCount;
        for (int i = 0; i < count; i++) {
            final View child = children[i];
            // Children that are clickable on their own should not
            // show a pressed state when their parent view does.
            // Clearing a pressed state always propagates.
            if (!pressed || (!child.isClickable() && !child.isLongClickable())) {
                child.setPressed(pressed);
            }
        }
    }

可以看出sdk16以后如果子view是!isClickable，父view是isClickable（父view如果是!isClickable都不会处理ACTION_DOWN事件），则即使在子view区域外的点击也会触发子view的pressed行为。这样改的原因不得而知，但个人觉得这不是正常期望的，UI表现上来看，父view点击任何区域子view都会触发pressed。

这种情景是存在的，比如子view是不可点，但又要设置父view可点以防点击父view会触发父父view事件。如果要处理这种情况，父view可以覆盖dispatchSetPressed方法进行重写，或者直接父view设置setEnable(false)。

android, lj
Comments