Question

当我在“自定义列表”上单击任意项时，我将制作一个简单的音乐应用程序；当我单击“返回”按钮时，从顶部开始显示其列表视图。

我需要单击或我所在位置的listView位置

        //Getting List view.....
          listView = (ListView) findViewById(R.id.MyListView);
          myroot = FirebaseDatabase.getInstance().getReference("all");
        readVariable = new ArrayList<>();
        //Ends...............

        // save index and top position
        int index = listView.getFirstVisiblePosition();
        View v = listView.getChildAt(0);
        int top = (v == null) ? 0 : (v.getTop() - listView.getPaddingTop());

        // restore index and position
        listView.setSelectionFromTop(index, top);

    }




    //FireBase Work>>>>>>>>>>>>>>>>>>>
    @Override
    protected void onStart() {
        super.onStart();

        myroot.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                readVariable.clear();
                for (DataSnapshot artisSnapshot : dataSnapshot.getChildren()) {
                    ReadVariables read = artisSnapshot.getValue(ReadVariables.class);
                    readVariable.add(read);

                }
                CustomList adapter = new CustomList(MainActivity.this, readVariable);
                listView.setAdapter(adapter);

            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
                Toast.makeText(MainActivity.this,"Check your network",Toast.LENGTH_LONG).show();

            }
        });
    }
    //Ends>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
}

Answer 1

将Unhandled promise rejection和readVariable定义为全局变量。

adapter
删除

CustomList adapter; ArrayList<> readVariable = new ArrayList<>();

我们已经将readVariable定义为全局变量并对其进行了初始化。
从readVariable = new ArrayList<>();
中删除以下行
```
onDataChange
```

并像这样写在这里

CustomList adapter = new CustomList(MainActivity.this, readVariable);
listView.setAdapter(adapter);

现在在//Getting List view..... listView = (ListView) findViewById(R.id.MyListView); myroot = FirebaseDatabase.getInstance().getReference("all"); adapter = new CustomList(MainActivity.this, readVariable); listView.setAdapter(adapter); //Ends...............中写了setAdapter行，写下：

onDataChange

如何从另一个活动中按回取列表视图的滚动位置

1 个答案: