Question

我正在尝试检索在firebase中上传的信息。一些上传的数据包含一个imgURl，一些不包含。

我的数据库如下所示：

这是我用来检索数据的代码：

public class ListRequests extends AppCompatActivity {
    ListView listView;
    FirebaseDatabase database;
    DatabaseReference ref;
    DatabaseReference Mref;
    ArrayList<String>list;
    ArrayAdapter<String>adapter;
    Uri imgURI;
    req req1;
    Upload upload1;
    TextView textView;
    private static final String TAG = "ListRequests";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_list_requests);
        // req1=new req();
        upload1=new Upload();
        listView=(ListView)findViewById(R.id.listView);
        textView=findViewById(R.id.requestinfo);

        database= FirebaseDatabase.getInstance();

        ref=database.getReference("uploads");
        list = new ArrayList<>();
        adapter=new ArrayAdapter<String>(this,R.layout.requestinfo,R.id.requestinfo,list);

        DatabaseReference database = FirebaseDatabase.getInstance().getReference();
        DatabaseReference ref = database.child("uploads"); //ur child name of the database
        ref.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                for(DataSnapshot singleSnapshot : dataSnapshot.getChildren()){
                    upload1=singleSnapshot.getValue(Upload.class);

                    if(upload1.getmImageUrl().toString()!=""){
                        list.add("\n"+"   "+"Title: "+upload1.getTitle().toString()+"\n"
                            +"   "+"Content: "+upload1.getContent().toString()+"\n"+"   "+"Date: "+upload1.getDate().toString()+
                            "\n"+"   "+"Time:"+upload1.getTime().toString()+"\n"+"   "+"Location: "+upload1.getLocation().toString()+"\n"+"   "+
                            "Type of notification: "+ upload1.getTypeof()+"\n"+"   "+ "\n"+"  "
                            +"Status: "+ upload1.getStatus().toString()+"\n"+"   "+upload1.getmImageUrl().toString());
                    } else {
                        list.add("\n"+"   "+"Title: "+upload1.getTitle().toString()+"\n"
                            +"   "+"Content: "+upload1.getContent().toString()+"\n"+"   "+"Date: "+upload1.getDate().toString()+
                            "\n"+"   "+"Time:"+upload1.getTime().toString()+"\n"+"   "+"Location: "+upload1.getLocation().toString()+"\n"+"   "+
                            "Type of notification: "+ upload1.getTypeof()+"\n"+"   "+ "\n"+"  "
                            +"Status: "+ upload1.getStatus().toString()+"\n"+"   ");
                    }
                }
                listView.setAdapter(adapter);
            }
            @Override
            public void onCancelled(DatabaseError databaseError) {
                Log.e(TAG, "onCancelled", databaseError.toException());
            }
        });
    }
}

由于upload1.getmImageUrl().toString()，某些数据未检索到ImgURl并导致程序崩溃。

如果它包含ImgURl，我想要检索所有的childern。有没有人有解决方案，我如何检索所有数据？

以下是我在日志中遇到的错误：

04-10 13:11:35.282 17684-17684/com.example.hp.upload E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.hp.upload, PID: 17684
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.String.toString()' on a null object reference
    at com.example.hp.upload.ListRequests$1.onDataChange(ListRequests.java:60)
    at com.google.firebase.database.zzp.onDataChange(Unknown Source)
    at com.google.android.gms.internal.to.zza(Unknown Source)
    at com.google.android.gms.internal.vj.zzHX(Unknown Source)
    at com.google.android.gms.internal.vp.run(Unknown Source)
    at android.os.Handler.handleCallback(Handler.java:751)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:154)
    at android.app.ActivityThread.main(ActivityThread.java:6692)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1468)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358)

Answer 1

我已更新答案，试一试

DatabaseReference database = FirebaseDatabase.getInstance().getReference();
DatabaseReference ref = database.child(""); //ur child name of the database

ref.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
    for(DataSnapshot singleSnapshot : dataSnapshot.getChildren()){
       upload1=singleSnapshot.getValue(Upload.class);

        if(upload1.getmImageUrl().toString()!=""){
          System.out.println("Location: "+upload1.getLocation().toString()+"\n"+"   "+"   "+upload1.getmImageUrl().toString());
          list.add(upload1.getmImageUrl().toString());
        } else {
             list.add(upload1.getLocation().toString());
        }
    }
    listView.setAdapter(adapter);
}
@Override
public void onCancelled(DatabaseError databaseError) {
    Log.e(TAG, "onCancelled", databaseError.toException());
}
});

检索firebase数据库中的节点

1 个答案: