Question

我有一个Android活动，其中包含RecyclerView，基本上，我正在创建一个音乐播放器应用。在这里，上一首歌曲按钮应该找到RecyclerView的上一元素，然后单击它（将播放歌曲），为此，当我使用recyclerView.getChildAt()时，它返回null，结果是错误。

以下是“上一个”按钮的onClickListener的代码...

prevSong_bottomSheet.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            // We start by checking if this is the first song or not!
            if (songIndex.getCurrentIndex() == 0) {
                Toast.makeText(MainActivity.this, "Nothing to play before this", Toast.LENGTH_SHORT).show();

                // Now, this simply return as we don't want to execute any of the following code!
                return;
            }

            Log.d(DEBUG_MESSAGE, "Original song index: " + songIndex.getCurrentIndex());

            try {
                // First, as we know that we'll be playing the previous audio, we start by decrementing
                //  the value inside `SongIndex`.
                songIndex.prevSongPlayed();

                // As the value inside `SongIndex` has been decremented, we use the same here!
                View parentView = recyclerView.getChildAt(songIndex.getCurrentIndex());
                // Now we extract the action button associated with this particular view!
                Button tempButton = parentView.findViewById(R.id.music_actionButton);

                // Now that we've got the button, instead of calling `startSong()` directly, we'll
                //  perform a click on the button, this way if we decide to perform some other action (in the future)
                //  once the user clicks that button, the action would still be valid!
                tempButton.performClick();
                Log.d(DEBUG_MESSAGE, "Previous song played successfully!");
            } catch (NullPointerException e) {
                // Lastly, if any error occurred in the above code, in the first line itself, we
                //  have already decremented SongIndex in the first line itself, thus, we increment
                //  it here to balance it out!
                //songIndex.nextSongPlayed();
                Log.d(DEBUG_MESSAGE, e.getLocalizedMessage() + "\n\n\n\n\n\n");
                e.printStackTrace();

                Log.d(DEBUG_MESSAGE, "Final song index: " + songIndex.getCurrentIndex());

            }
        }
    });

运行上面的代码时，只要RecyclerView的下一个元素出现在屏幕上，它就可以完美运行，但是当视图不在屏幕上时，它将开始返回null！

是的，我知道RecyclerView会破坏屏幕外的元素（甚至不会创建它们）。要解决此问题，我尝试使用recyclerView.scrollToPosition()，即使这样做后，它仍返回null。我试图向上滚动到上一个元素的位置，甚至在其上方的2或3个位置上，仍然getChildAt()返回null。除此之外，即使在这个getChildAt()返回空值之后，我也试图阻塞主线程以等待RecyclerView向上滚动（使用无限循环）。

我该如何解决？

P.S。 songIndex是一个类，用于保持当前正在播放的歌曲位置的标签。这是它的代码（以防万一）：

private class SongIndex {
    /**
     * This class is used to keep a track as to which song is being played currently, the data member
     * created inside this class would be regularly updated using the functions defined below!
     * Thus, this class will be used at various instances inside the program to know about the
     * index of the song (inside the RecyclerView) which is being played currently!
     */

    private int currentSongIndex;

    public int getCurrentIndex() {
        return currentSongIndex;
    }

    public void setCurrentSongIndex(int currentSongIndex) {
        this.currentSongIndex = currentSongIndex;
    }

    public void nextSongPlayed() {
        currentSongIndex++;
    }

    public void prevSongPlayed() {
        currentSongIndex--;
    }
}

PSS我试图解决的另一件事是，当我到达屏幕顶部时（上方会有更多元素，但是它们都不会出现在屏幕上，即RecyclerView可能会破坏它们），之后，我手动向上滚动，以使当前播放的歌曲位于屏幕的中间（现在它上面有元素），即使现在，当我尝试上一个按钮时，我仍然以某种方式结束了{{1 }}部分：（

Answer 1

根据您共享的代码，currentSongIndex未初始化。它将具有一些垃圾值，因此您的if条件（songIndex.getCurrentIndex（）== 0）首次为false，并且songIndex.getCurrentIndex（）将返回垃圾，因此recyclerView.getChildAt（songIndex.getCurrentIndex（））;将为空

Android：即使对象在屏幕上，RecyclerView`getChildAt（）`也会返回null

1 个答案: