java - RecyclerView 在我第一次进入 Activity 时不填充，但在我退出并重新进入 Activity 后显示

Question

正如标题所描述的，我需要第一次进入 Activity 到空白屏幕。然后，我需要通过按返回退出 Activity 并再次重新进入 Activity 才能看到回收器 View 。幸运的是，当填充回收器 View 时，一切都井井有条，并且它准确地显示了我希望它在屏幕上显示的方式。

这是我的 Activity 类(class):

 @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.hosting_trip);

    mOwnTripList = (RecyclerView) findViewById(R.id.host_trip_list);
    mOwnTripList.setHasFixedSize(true);
    mOwnTripList.setLayoutManager(new LinearLayoutManager(this));

 mPostIdRef.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

            comPostArrayList.clear();
            for (DataSnapshot snapshot : dataSnapshot.getChildren()) {

                PostId postId = snapshot.getValue(PostId.class);
                    tripUniqueId = postId.getPostId();
                Log.d("$$$$$$$$$$$$$" , tripUniqueId);



        mLastRef = FirebaseDatabase.getInstance().getReference().child("comPostsCopy")
                   .child(tripUniqueId);

        mLastRef.addListenerForSingleValueEvent(new ValueEventListener() {
         @Override
         public void onDataChange(DataSnapshot dataSnapshot) {


         OwnHostTripItem ownHostTripPost = dataSnapshot
                                         .getValue(OwnHostTripItem.class);
              comPostArrayList.add(ownHostTripPost);
            Log.d("%%%%%",comPostArrayList.get(0).getTitle());

        }

         @Override
         public void onCancelled(DatabaseError databaseError) {

            }
         });

            }

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

     adapter = new YourHostAdapter( comPostArrayList , this.getApplicationContext());

    adapter.notifyDataSetChanged();

    mOwnTripList.setAdapter(adapter);

} 
  }

这是我的模型类:

  public class OwnHostTripItem {

String thumbPhoto;
String title;
String country;
String pricePerGuest;
String maxGroupSize;

public OwnHostTripItem() {

}

public OwnHostTripItem(String thumbPhoto, String title, String country, String pricePerGuest
                        , String maxGroupSize) {
    this.thumbPhoto = thumbPhoto;
    this.title = title;
    this.country = country;
    this.pricePerGuest = pricePerGuest;
    this.maxGroupSize = maxGroupSize;
}



public String getThumbPhoto() {
    return thumbPhoto;
}

public void setThumbPhoto(String thumbPhoto) {
    this.thumbPhoto = thumbPhoto;
}

public String getTitle() {
    return title;
}

public void setTitle(String title) {
    this.title = title;
}

public String getCountry() {
    return country;
}

public void setCountry(String country) {
    this.country = country;
}

public String getPricePerGuest() {
    return pricePerGuest;
}

public void setPricePerGuest(String pricePerGuest) {
    this.pricePerGuest = pricePerGuest;
}

public String getMaxGroupSize() {
    return maxGroupSize;
}

public void setMaxGroupSize(String maxGroupSize) {
    this.maxGroupSize = maxGroupSize;
}

}

这是我的适配器:

 public class YourHostAdapter extends RecyclerView.Adapter<YourHostAdapter.ViewHolder> {

private ArrayList<OwnHostTripItem> ownHostTripList;
private Context context;

public YourHostAdapter(ArrayList<OwnHostTripItem> ownHostTripList, Context context) {
    this.ownHostTripList = ownHostTripList;
    this.context = context;
}

@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View v = LayoutInflater.from(parent.getContext())
             .inflate(R.layout.host_trip_item, parent , false);
    return new ViewHolder(v);
}

@Override
public void onBindViewHolder(ViewHolder holder, int position) {
    OwnHostTripItem ownHostTripListy = ownHostTripList.get(position);

    holder.mTripTitle.setText(ownHostTripListy.getTitle());
    holder.mTripCountry.setText(ownHostTripListy.getCountry());
    holder.mTripPrice.setText(ownHostTripListy.getPricePerGuest());
    holder.mTripSize.setText(ownHostTripListy.getMaxGroupSize());

    //For Image view
    Picasso.with(context).load(ownHostTripListy.getThumbPhoto())
    .placeholder(R.drawable.placeholder_image).into(holder.mTripImage)


}

@Override
public int getItemCount() {
    return ownHostTripList.size();
}

public class ViewHolder extends RecyclerView.ViewHolder{

    View mView;
    public TextView mTripTitle;
    public TextView mTripCountry;
    public TextView mTripPrice;
    public TextView mTripSize;
    public ImageView mTripImage;

    public ViewHolder(View itemView) {
        super(itemView);

        mView = itemView;

        mTripTitle = (TextView) mView.findViewById(R.id.host_trip_title);
        mTripCountry = (TextView) mView.findViewById(R.id.host_trip_country);
        mTripPrice = (TextView) mView.findViewById(R.id.host_trip_price);
        mTripSize = (TextView) mView.findViewById(R.id.host_trip_size);

        mTripImage = (ImageView) mView.findViewById(R.id.host_trip_image);

          }
        }
       }

这是我的 xml，其中包含回收器 View :

 <?xml version="1.0" encoding="utf-8"?>
   <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">


    <include layout="@layout/app_bar_layout"
        android:id="@+id/hosting_trip_bar"
        />

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Oops, looks like you haven't been hosting any trips"
        android:layout_centerVertical="true"
        android:layout_alignParentStart="true"
        android:layout_marginStart="10dp"
        android:layout_marginEnd="10dp"
        android:id="@+id/hosting_trip_text"
        />


    <android.support.v7.widget.RecyclerView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/host_trip_list"
        android:layout_below="@id/hosting_trip_bar"
        android:layout_marginTop="10dp" />


      </RelativeLayout>

我尝试在 onStart 方法中设置适配器，并且我看到其他帖子指出我们需要在 xml 中设置回收器 View 以匹配父级，但它给了我相同的结果。正如您所看到的，我没有将 RecyclerView 嵌套在许多 View 中。难道是我在错误的时间设置了适配器，所以它给了我一个空列表？

Answer 1

“hosting_trip.xml”文件中的 recyclerview 有问题。您应该将 recyclerview 的高度更改为 match_parent (android:layout_height="match_parent")。

因为您尚未上传您的hosting_trip.xml 文件。您可以尝试让我知道解决方案。