Question

我正在尝试实施Firebase Android聊天，仅当带有邮件的ListView滚动到显示新邮件的底部时才会更新。（这就是聊天如何在抽搐中起作用，让用户舒服地阅读旧信息）。

这是我试过的：

MyFirebaseListAdapter （已修改的FirebaseListAdapter）

public abstract class MyFirebaseListAdapter<T> extends BaseAdapter {
    ...
    MyFirebaseArray mSnapshots;
    ...
    public void setShouldUpdate(boolean b) {
        if (b) {
            mSnapshots.addEventListener();
        } else {
            mSnapshots.removeEventListener();
        }
    }
    ...
}

MyFirebaseArray （已修改的FirebaseArray）

class MyFirebaseArray implements ChildEventListener {
    ...
    private boolean hasEventListener = false;
    ...
    public void removeEventListener() {
        if (!hasEventListener) return;
        hasEventListener = false;
        mQuery.removeEventListener(this);
    }
    public void addEventListener() {
        if (hasEventListener) return;
        hasEventListener = true;
        mSnapshots.clear();
        mQuery.addChildEventListener(this);
    }
    ...
}

ChatActivity

final MyFirebaseListAdapter adapter = new MyFirebaseListAdapter<ChatMessage>(ChatActivity.this, ChatMessage.class, R.layout.li_chat_message, db.child("/messages/" + room.key).limitToLast(40)) {
    @Override
    protected void populateView(View v, final ChatMessage msg, int position) {
        ChatUtils.layoutChatMessage(ChatActivity.this, db, user, status, v, msg, bgColor, new View.OnLongClickListener() {
            @Override
            public boolean onLongClick(View view) {
                etMessage.setText(msg.author.name + ", ");
                return false;
            }
        });
    }
};
lvMessages.setAdapter(adapter);
lvMessages.setOnScrollListener(new AbsListView.OnScrollListener() {
    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) { }

    @Override
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
        if (firstVisibleItem + visibleItemCount == totalItemCount) {
            adapter.setShouldUpdate(true);
        } else {
            adapter.setShouldUpdate(false);
        }
    }
});

但是，如果我在底部更改滚动方向太快，则会引发以下异常：

AndroidRuntime: FATAL EXCEPTION: main
java.lang.IndexOutOfBoundsException: Invalid index 34, size is 0
at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:255)
at java.util.ArrayList.get(ArrayList.java:308)
at com.kg.app.***.chat.adapter.MyFirebaseArray.getItem(MyFirebaseArray.java:80)
at com.kg.app.***.chat.adapter.MyFirebaseListAdapter.getItem(MyFirebaseListAdapter.java:117)
at com.kg.app.***.chat.adapter.MyFirebaseListAdapter.getView(MyFirebaseListAdapter.java:147)
at android.widget.AbsListView.obtainView(AbsListView.java:2347)
at android.widget.ListView.makeAndAddView(ListView.java:1864)
at android.widget.ListView.fillUp(ListView.java:732)
at android.widget.ListView.correctTooHigh(ListView.java:1421)
at android.widget.ListView.fillGap(ListView.java:663)
at android.widget.AbsListView.trackMotionScroll(AbsListView.java:4995)
at android.widget.AbsListView$FlingRunnable.run(AbsListView.java:4543)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
at android.view.Choreographer.doCallbacks(Choreographer.java:580)
at android.view.Choreographer.doFrame(Choreographer.java:549)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:211)
at android.app.ActivityThread.main(ActivityThread.java:5389)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1020)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:815)

更新

我知道抛出异常是因为我在addEventListener（）方法中清除了mSnapshots数组。但是，如果我删除此行，则每次调用addEventListener时，所有记录都会重复。此外，如果我慢慢滚动我的解决方案工作正常。

滚动列表视图时如何防止FirebaseListAdapter更新？

0 个答案: