我正在开发一个简单的APOD应用程序,它实现：
> RecyclerView
> CardView
> Firebase
毕加索
该应用程序从Firebase和Firebase Storage中抓取图像和文本,将它们显示在CardView中,并将OnClickListener设置为每个视图.当用户点击图像时,我通过意图打开一个新的活动.第二个活动显示原始点击的图像,以及更多关于它的信息.
如果用户的手机是VERTICAL,我已经实现了这一切,使用GridLayoutManager 1列,如果用户的手机是HORIZONTAL,则列3列.
我遇到的问题是,似乎无法保存RecyclerView对方向更改的立场.我已经尝试过我可以找到的每一个选项,但没有一个看起来不起作用.我唯一可以想出的结论是,在旋转时,我正在销毁Firebase的ChildEventListener以避免内存泄漏,一旦方向完成,Firebase将重新查询数据库,因为新的ChildEventListener实例.
有没有什么办法可以节省我的RecyclerView的方向改变的立场？我不想要android：configChanges,因为它不会让我改变我的布局,我已经尝试保存为一个包裹,这是不成功的.我确定这是一件容易的东西,我失踪了,但嘿,我很开心.对我的代码的任何帮助或建议非常感谢.谢谢！
以下是我的课程,我只缩写为必需的代码.
主要活动
public class MainActivity extends AppCompatActivity {
private RecyclerAdapter mRecyclerAdapter;
private DatabaseReference mDatabaseReference;
private RecyclerView mRecyclerView;
private Query query;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
PreferenceManager.setDefaultValues(this,R.xml.preferences,false);
setContentView(R.layout.activity_main);
getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
final int columns = getResources().getInteger(R.integer.gallery_columns);
mDatabaseReference = FirebaseDatabase.getInstance().getReference();
query = mDatabaseReference.child("apod").orderByChild("date");
mRecyclerView = (RecyclerView) findViewById(R.id.recycler_view);
mRecyclerView.setHasFixedSize(true);
mRecyclerView.setLayoutManager(new GridLayoutManager(this,columns));
mRecyclerAdapter = new RecyclerAdapter(this,query);
mRecyclerView.setAdapter(mRecyclerAdapter);
}
@Override
public void onDestroy() {
mRecyclerAdapter.cleanupListener();
}
}
RecyclerAdapter
public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.ApodViewHolder> {
private final Context mContext;
private final ChildEventListener mChildEventListener;
private final Query mDatabaseReference;
private final List<String> apodListIds = new ArrayList<>();
private final List<Apod> apodList = new ArrayList<>();
public RecyclerAdapter(final Context context,Query ref) {
mContext = context;
mDatabaseReference = ref;
ChildEventListener childEventListener = new ChildEventListener() {
@Override
public void onChildAdded(DataSnapshot dataSnapshot,String s) {
int oldListSize = getItemCount();
Apod apod = dataSnapshot.getValue(Apod.class);
//Add data and IDs to the list
apodListIds.add(dataSnapshot.getKey());
apodList.add(apod);
//Update the RecyclerView
notifyItemInserted(oldListSize - getItemCount() - 1);
}
@Override
public void onChildChanged(DataSnapshot dataSnapshot,String s) {
}
@Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
String apodKey = dataSnapshot.getKey();
int apodIndex = apodListIds.indexOf(apodKey);
if (apodIndex > -1) {
// Remove data and IDs from the list
apodListIds.remove(apodIndex);
apodList.remove(apodIndex);
// Update the RecyclerView
notifyDataSetChanged();
}
}
@Override
public void onChildMoved(DataSnapshot dataSnapshot,String s) {
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
};
ref.addChildEventListener(childEventListener);
mChildEventListener = childEventListener;
}
@Override
public int getItemCount() {
return apodList.size();
}
public void cleanupListener() {
if (mChildEventListener != null) {
mDatabaseReference.removeEventListener(mChildEventListener);
}
}
}
解决方法
当旋转活动再次被破坏并再次创建时,意味着所有的对象都被破坏并重新创建,并且再次重新绘制布局.
你想停止重新创建活动,你可以使用android：configChanges,但它是不好的做法,也不是正确的方式.
只有事情现在仍然存在,以在旋转之前保存回收者视图的位置,并在活动重新创建之后获取它.
//保存回收者的位置
@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
// Save UI state changes to the savedInstanceState.
// This bundle will be passed to onCreate if the process is
// killed and restarted.
savedInstanceState.putInt("position",mRecyclerView.getAdapterPosition()); // get current recycle view position here.
super.onSaveInstanceState(savedInstanceState);
}
//恢复值
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
PreferenceManager.setDefaultValues(this,query);
mRecyclerView.setAdapter(mRecyclerAdapter);
if(savedInstanceState != null){
// scroll to existing position which exist before rotation.
mRecyclerView.scrollToPosition(savedInstanceState.getInt("position"));
}
}
希望这些帮助你.
