java-在片段上的GridView中显示从Firebase下载的图像在打开片段时不断崩溃

我正在使用我们位于导航抽屉中的一个片段上的GridView为我们的android应用创建图库.我为图像视图创建了一个自定义适配器,该适配器使用Picasso在图像视图中显示图像.我制作了一种名为DohvatiSlike()的方法,该方法从firebase下载图像并将其保存在File变量中.当我构建应用程序并运行它时,每当我从导航抽屉中打开图库时,应用程序都会崩溃.如果我在onCreateView中排除设置GalleryGridAdapter的行,则不会崩溃,但显然不起作用.谁能帮我发现问题？

这是GalleryFragment代码：

public class GalleryFragment extends Fragment implements NavigationItem {
private DatabaseReference mDatabaseRef;
private List<File> slike;
private int position;
GridView galleryGridView;
@Override
public View onCreateView(LayoutInflater inflater,ViewGroup container,Bundle savedInstanceState) {
    View v = inflater.inflate(R.layout.gallery_fragment,container,false);
    super.onCreateView(inflater,savedInstanceState);

    galleryGridView = (GridView)v.findViewById(R.id.gallery_gridview);
    DohvatiSlike();
    galleryGridView.setAdapter(new GalleryGridAdapter(getActivity(),slike));

    return v;
}

public void DohvatiSlike(){
    mDatabaseRef=FirebaseDatabase.getInstance().getReference("images");
    mDatabaseRef.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for(DataSnapshot postSnapshot: dataSnapshot.getChildren()){
                File slika = postSnapshot.getValue(File.class);
                slike.add(slika);
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            Toast.makeText((AppCompatActivity)getActivity(),databaseError.getMessage(),Toast.LENGTH_SHORT).show();
        }
        });}

@Override
public void onAttach(Activity activity){
    super.onAttach(activity);
}

这是适配器代码：

public class GalleryGridAdapter extends BaseAdapter {
private Context mContext;
public List<File> slike;

public GalleryGridAdapter(Context context,List<File> slikice){
    slike = slikice;
    mContext = context;
}

@Override
public int getCount() {
    return slike.size();
}

@Override
public Object getItem(int position) {
    return slike.indexOf(position);
}

@Override
public long getItemId(int position) {
    return 0;
}

@Override
public View getView(int position,View convertView,ViewGroup parent) {
    ImageView imageView;
    if (convertView == null) {
        imageView = new ImageView(mContext);
        imageView.setLayoutParams(new GridView.LayoutParams(500,500));
        imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
    } else{
        imageView = (ImageView) convertView;
    }
        Picasso.with(mContext).load(slike.indexOf(position)).into(imageView);
        return imageView;
}

}

编辑*

这是崩溃日志

 Process: hr.foi.air1817.botanico,PID: 26065
java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
    at hr.foi.air1817.botanico.adapters.GalleryGridAdapter.getCount(GalleryGridAdapter.java:26)
    at android.widget.GridView.setAdapter(GridView.java:211)
    at hr.foi.air1817.botanico.fragments.GalleryFragment$1.onDataChange(GalleryFragment.java:62)
    at com.google.firebase.database.obfuscated.zzap.zza(com.google.firebase:firebase-database@@16.0.3:75)
    at com.google.firebase.database.obfuscated.zzca.zza(com.google.firebase:firebase-database@@16.0.3:63)
    at com.google.firebase.database.obfuscated.zzcd$1.run(com.google.firebase:firebase-database@@16.0.3:55)
    at android.os.Handler.handleCallback(Handler.java:873)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:193)
    at android.app.ActivityThread.main(ActivityThread.java:6863)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:537)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

我已经连续两天在这里工作了,只是无法正常工作,建议或想法受到赞赏

最佳答案

这是异步操作的一个常见问题,您的代码将始终崩溃,因为在执行此操作时,您需要先设置适配器数据,然后再从Firebase中获取适配器数据

DohvatiSlike();
    galleryGridView.setAdapter(new GalleryGridAdapter(getActivity(),slike));

方法DohvatiSlike();仍在请求数据,并且可能无法在您拥有的类似数组上添加元素.

而是在您的DohvatiSlike()中移动适配器的设置.方法

     public void DohvatiSlike(){

           slike = new List<>();                


  mDatabaseRef = FirebaseDatabase.getInstance().getReference("images");
                mDatabaseRef.addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {

                        for(DataSnapshot postSnapshot: dataSnapshot.getChildren()){
                            File slika = postSnapshot.getValue(File.class);
                            slike.add(slika);
                        }

                    galleryGridView.setAdapter(new GalleryGridAdapter(getActivity(),slike));

                    }

                    @Override
                    public void onCancelled(DatabaseError databaseError) {
                        Toast.makeText((AppCompatActivity)getActivity(),Toast.LENGTH_SHORT).show();
                    }
                    });
            }

当执行DohvatiSlike()时,您将需要等待,具体取决于您的Internet连接以获取该数据,在获取数据之后,您将填充阵列,在这种情况下,您是在请求数据并立即用可能没有配置的数据设置适配器.尚未获取,而是只需在解析所有数据并将其添加到onDataChange内部之后再设置适配器.

另外,在显示视图时,请在onViewCreated()内进行操作,因为onCreateView()仅用于放大视图元素