android - recyclerview 的 findFirstVisibleItemPosition() 总是返回 -1

Question

这是我想在方向更改和 Activity 恢复时保留 recyclerview 滚动位置的代码。问题出在我的日志中，我总是得到-1。我哪里错了？

void resetViews() {
    recyclerView.setAdapter(adapter);
    recyclerView.setLayoutManager(new LinearLayoutManager(getApplicationContext()));
    RecyclerView.LayoutManager lm =  recyclerView.getLayoutManager();
    if (lm != null && lm instanceof  LinearLayoutManager) {
        currPosition = ((LinearLayoutManager)lm).findFirstVisibleItemPosition();
        Log.i("saz","curr pos : " + currPosition);
    }
    int count = lm.getChildCount();
    if (currPosition != RecyclerView.NO_POSITION && currPosition < count){
        lm.scrollToPosition(currPosition);
    }
}

Answer 1

一切都非常简单，因为您重载了适配器，LayoutManager 没有时间在其内部构建元素，这意味着此时所有元素在屏幕上都不可见。如果您尝试调用 recyclerView.getChildCount()，您将得到 0。

尝试这样的事情:

recyclerView.setAdapter(adapter);
recyclerView.setLayoutManager(new LinearLayoutManager(getApplicationContext()));
new Handler().postDelayed(new Runnable(){
        public void run() {
            RecyclerView.LayoutManager lm = recyclerView.getLayoutManager();
            if (lm != null && lm instanceof LinearLayoutManager) {
                currPosition = ((LinearLayoutManager)lm).findFirstVisibleItemPosition();
                Log.i("saz","curr pos : " + currPosition);
            }
            int count = lm.getChildCount();
            if (currPosition != RecyclerView.NO_POSITION && currPosition < count){
                lm.scrollToPosition(currPosition);
            }
        }
    }, 500);