Android - the item inside RecyclerView can't b

问题:

I just upgraded to API 26 and support library 26.0.2. But I found that my RecyclerView items is not clickable right after the scrolling. If you wait for a second, it will work. But if you click the item immediately, it won't. Even if the RecyclerView is not scrolling at all(e.g. has scrolled to the top).

When I downgraded to support library 25.4.0 everything goes fine again. The key point is that my RecyclerView is in a CoordinatorLayout and has a SCROLL_FLAG_SCROLL flag on my Toolbar of the AppBarLayout. If I don't use this flag, then this problem will disappear. So I think it's a hidden behavior change of support library 26.

I've tried to add focusable="false" to the CoordinatorLayout but still had no luck.

Is there any way to disable this behavior? Because it's really annoying to click twice to trigger the click event.

 <android.support.design.widget.CoordinatorLayout
        android:id="@+id/coordinateLayout"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    <android.support.design.widget.AppBarLayout
            android:id="@+id/fragmentAppBar"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:elevation="0dp"
            android:background="@null">
        <include
                android:id="@+id/dynamicActionBarHolder"
                layout="@layout/dynamic_action_bar"/>
    </android.support.design.widget.AppBarLayout>

    <android.support.v4.widget.SwipeRefreshLayout
            android:id="@+id/pullToRefreshMailRecycler"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_behavior="@string/appbar_scrolling_view_behavior">

        <android.support.v7.widget.RecyclerView
                android:id="@+id/mailRecyclerView"
                android:layout_width="match_parent"
                android:layout_height="match_parent"/>

    </android.support.v4.widget.SwipeRefreshLayout>

</android.support.design.widget.CoordinatorLayout>

EDIT

I think the problem is the scrollState of the RecyclerView. When it's stopped scrolling, it's not changed to SCROLL_STATE_IDLE immediately. Looking into the source code of RecyclerView, I found there's a ViewFlinger controlling the scroll state. When I fling down to scroll to the top, it's not calling setScrollState(SCROLL_STATE_IDLE) immediately, instead, it wait for a while to trigger this method. The more fast I fling, the more time I need to wait. It just like the RecyclerView is still scrolling in the background. Because the scroller.isFinished() doesn't return true right after the RecyclerView stop scrolling when it touched the top. Maybe it's a bug of the RecyclerView when it's in a CoordinatorLayout.

回答1:

Found a way to force the scroll state to be idle. Waiting for google to fix this bug.

@Override
public boolean onInterceptTouchEvent(MotionEvent event) {
    boolean requestCancelDisallowInterceptTouchEvent = getScrollState() == SCROLL_STATE_SETTLING;
    boolean consumed = super.onInterceptTouchEvent(event);
    final int action = event.getActionMasked();

    switch (action) {
        case MotionEvent.ACTION_DOWN:
            if( requestCancelDisallowInterceptTouchEvent ){
                getParent().requestDisallowInterceptTouchEvent(false);

                // only if it touched the top or the bottom. Thanks to @Sergey's answer.
                if (!canScrollVertically(-1) || !canScrollVertically(1)) {
                    // stop scroll to enable child view to get the touch event
                    stopScroll();
                    // do not consume the event
                    return false;
                }
            }
            break;
    }

    return consumed;
}

EDIT

The issue has been fixed in support library 27.0.1.

https://developer.android.com/topic/libraries/support-library/revisions.html#27-0-1

After a user scrolls, they cannot click on an item in a RecyclerView. (AOSP issue 66996774)

Updated on Nov 17, 2017

Some users reported that this problem is not fixed in support library 27.0.1. The issue tracker is here. https://issuetracker.google.com/issues/66996774

So you may choose to use this official workaround. https://gist.github.com/chrisbanes/8391b5adb9ee42180893300850ed02f2

Or use this one here.

回答2:

Thank you very much for this question and your answer! It saved me a lot of time. Sorry for posting this as an answer. I don't have enough reputation to comment.

I also noticed this issue, but as a new Android developer I didn't realize it's a bug inside the new support library.

What I wanted to suggest is also adding this check:

if( requestCancelDisallowInterceptTouchEvent ){
    if (!canScrollVertically(-1) || !canScrollVertically(1)) {
        ...
    }
}

It will make sure that while the RecyclerView is actually being scrolled, we don't click on any item.

As I understand, it's an expected behaviour. However, your answer helped me with this question.

回答3:

I have found a source code that solved this issue. This issue occur because of AppBarLayout's behavior (AppBarLayout.Behavior). This source code provide an extending or a customizing behavior of behavior of AppBarLayout and set it into the AppBarLayout with introduction of usage both in xml directly or java. I can only explain briefly about it because the source has license that you must read it too. Please see the solution in this link: https://gist.github.com/chrisbanes/8391b5adb9ee42180893300850ed02f2