android - Firebase 不向 ListView 显示数据

Question

我正在尝试为大学类(class)制作一个 Android 应用程序，我需要显示来自 firebase 数据库的信息并将其显示在 ListView 中。我进行了很多搜索，但找不到任何可以帮助我的东西。我需要帮助。该应用程序向我发送了某种类型的错误，但我无法找出问题所在。我现在需要获取产品的每个名称并将其显示在 ListView 中。顺便说一句，我是 Android Studio 的新手。

This my database of firebase

这是我的 Activity :

public class buscador extends AppCompatActivity {

ListView lv;
private DatabaseReference myRef,ref,ref2;
private FirebaseAuth mAuth;
private FirebaseAuth.AuthStateListener mAuthListner;
private String id;
private FirebaseDatabase mFirebaseDatabase;
private static final String TAG = "buscador";
int num=1;
private ArrayList<String> array2;

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

    lv=(ListView)findViewById(R.id.cat1);
    EditText search = (EditText)findViewById(R.id.searchfind);
    mAuth=FirebaseAuth.getInstance();
    FirebaseUser user=mAuth.getCurrentUser();
    id=ref.getKey();

    setupFirebaseAuth();


    ref=FirebaseDatabase.getInstance().getReference("Products");
    ref.addValueEventListener(new ValueEventListener() {
        @Override
       public void onDataChange(DataSnapshot dataSnapshot) {
            showData(dataSnapshot);
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
}
public void showData(DataSnapshot dataSnapshot){
    for (DataSnapshot ds : dataSnapshot.getChildren()) {
        Producto info = new Producto();
        info.setName(ds.child(id).getValue(Producto.class).getName());

        Log.d(TAG, "showData:name:" + info.getName());
        ArrayList<String> array=new ArrayList<>();
        array.add(info.getName());
        ArrayAdapter adapter=new ArrayAdapter(this,android.R.layout.simple_list_item_1,array);
        lv.setAdapter(adapter);}
}

Producto 类对象:

public class Producto {
private String image;
private String name;
private float price;
private String descripcion;
private String catalogo;
private String id;

public Producto(String image, String name, float price, String descripcion, String catalogo, String id) {
    this.image = image;
    this.name = name;
    this.price = price;
    this.descripcion = descripcion;
    this.catalogo = catalogo;
    this.id = id;
}

public Producto() {
}

public String getImage() {
    return image;
}

public void setImage(String image) {
    this.image = image;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public float getPrice() {
    return price;
}

public void setPrice(float price) {
    this.price = price;
}

public String getDescripcion() {
    return descripcion;
}

public void setDescripcion(String descripcion) {
    this.descripcion = descripcion;
}

public String getCatalogo() {
    return catalogo;
}

public void setCatalogo(String catalogo) {
    this.catalogo = catalogo;
}

public String getId() {
    return id;
}

public void setId(String id) {
    this.id = id;
}
    }

错误:

  Process: com.example.roge.navapp, PID: 32020

java.lang.RuntimeException: Unable to start activity 
ComponentInfo{com.example.roge.navapp/com.example.roge.navapp.buscador}: 
java.lang.NullPointerException                                                                             
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2429)                                                                             
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2493)                                                                             
at android.app.ActivityThread.access$800(ActivityThread.java:166)                                                                             
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1283)                                                                             
at android.os.Handler.dispatchMessage(Handler.java:102)                                                                             
at android.os.Looper.loop(Looper.java:136)                                                                             
at android.app.ActivityThread.main(ActivityThread.java:5590)                                                                             
at java.lang.reflect.Method.invokeNative(Native Method)                                                                             
at java.lang.reflect.Method.invoke(Method.java:515)                                                                             
at Com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1268)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1084)                                                                             
at dalvik.system.NativeStart.main(Native Method)                                                                          
Caused by: java.lang.NullPointerException                                                                             
at com.example.roge.navapp.buscador.onCreate(buscador.java:51)                                                                             
at android.app.Activity.performCreate(Activity.java:5447)                                                                             
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)

Answer 1

要从您的 Firebase 数据库中获取 name，请使用以下代码:

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference productsRef = rootRef.child("Products");
ValueEventListener eventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        List<String> list = new ArrayList<>();
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            String name = ds.child("name").getValue(String.class);
            list.add(name);
            Log.d("TAG", name);
        }
        Log.d("TAG", list);
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {}
};
productsRef.addListenerForSingleValueEvent(eventListener);

你的输出将是:

ps4
Xbox
//and so on