java - FirebaseRecyclerAdapter getItemCount = 0

Question

我为 RecyclerView 创建了一个 FirebaseRecylerAdapter，我的问题是 FirebaseRecyclerAdapter 没有调用 onCreateViewHolder(因此 recyclerView 什么都不显示)。我在一些帖子上发现这是因为 getItemCount = 0 (在我的项目开始时我没有 getItemCount 方法)。所以我做到了，但它并没有解决我的问题，因为 getItemCount 返回 0，我不明白为什么。我可以正确地写入我的数据库，所以我知道我的数据库已成功连接，我运行到 Debug模式，我们可以看到。

主要 Activity .java:

    public class MainActivity extends AppCompatActivity {

private RecyclerView mTaskList;
private DatabaseReference mDatabase;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    mTaskList = findViewById(R.id.task_list);
    //mTaskList.setHasFixedSize(true);
    mTaskList.setLayoutManager(new LinearLayoutManager(this));
    mDatabase = FirebaseDatabase.getInstance().getReference().child("Tasks");

    FloatingActionButton fab = findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent intent = new Intent(MainActivity.this, AddTaskActivity.class);
            startActivity(intent);

        }
    });

}

public static class TaskViewHolder extends RecyclerView.ViewHolder{
    public TaskViewHolder(View itemView) {
        super(itemView);
        View mView = itemView;
    }
    public void setName(String name)
    {
        TextView task_name = itemView.findViewById(R.id.task_name);
        task_name.setText(name);

    }

    /*public void setTime(String time)
    {
        TextView task_time = itemView.findViewById(R.id.task_time);
        task_time.setText(time);
    }*/
}

@Override
protected void onStart() {
    super.onStart();
    Log.d("POS", "onStart: ");
    FirebaseRecyclerOptions<Task> options =
            new FirebaseRecyclerOptions.Builder<Task>()
                    .setQuery(mDatabase, Task.class)
                    .build();

    FirebaseRecyclerAdapter<Task, TaskViewHolder> array = new FirebaseRecyclerAdapter<Task, TaskViewHolder>(options) {

        @Override
        public int getItemCount() {
            Log.d("NB", "getItemCount: " + super.getItemCount());
            return super.getItemCount();
        }

        @Override
        protected void onBindViewHolder(TaskViewHolder holder, int position, Task model) {
            holder.setName(model.getName());
            Log.d("BIND", "onBindViewHolder: pass");
            //holder.setTime(model.getTime());

        }

        @Override
        public TaskViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.activity_main,
                    parent, false);
            Log.d("CREATE", "onCreate: pass");

            return new TaskViewHolder(view);
        }
    };
    array.notifyDataSetChanged();
    mTaskList.setAdapter(array);
}

任务.java :

    public class    Task {
private     String name;
//private     String time;

public Task(String name){
    this.name = name;
    //this.time = time;
}

public Task(){
}

public String getName() {
    return name;
}

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

添加任务 Activity .java :

public class AddTaskActivity extends AppCompatActivity {
private FirebaseDatabase db;
DatabaseReference myRef;
EditText editText;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.add_task);
    Toolbar toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_task, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    editText = findViewById(R.id.desc);
    String desc = editText.getText().toString();
    //noinspection SimplifiableIfStatement
    if (id == R.id.action_save) {
        myRef = db.getInstance().getReference().child("Tasks");
        DatabaseReference newTask = myRef.push();
        newTask.child("name").setValue(desc);
        AddTaskActivity.this.finish();
        return true;
    }

    return super.onOptionsItemSelected(item);
}

在此先感谢您，如果您需要更多信息，请告诉我。

和我启动 mainActivity 时的 logcat:

01-15 10:57:57.830 18882-18882/? W/SELinux: SELinux selinux_android_compute_policy_index : Policy Index[2],  Con:u:r:zygote:s0 RAM:SEPF_SECMOBILE_7.0_0009, [-1 -1 -1 -1 0 1]
01-15 10:57:57.832 18882-18882/? I/SELinux: SELinux: seapp_context_lookup: seinfo=untrusted, level=s0:c512,c768, pkgname=com.thauvi_a.todolist 
01-15 10:57:57.834 18882-18882/? I/art: Late-enabling -Xcheck:jni
01-15 10:57:57.854 18882-18882/? D/TimaKeyStoreProvider: TimaKeyStore is enabled: try add TimaSignature Service and generateKeyPair Service
01-15 10:57:57.883 18882-18882/? I/ResourcesManager: updateResourcesForOpenThemeChange for Desktop mode 
01-15 10:57:57.994 18882-18882/com.thauvi_a.todolist W/System: ClassLoader referenced unknown path: /data/app/com.thauvi_a.todolist-2/lib/arm64
01-15 10:57:58.013 18882-18882/com.thauvi_a.todolist D/FirebaseApp: com.google.firebase.auth.FirebaseAuth is not linked. Skipping initialization.
01-15 10:57:58.019 18882-18882/com.thauvi_a.todolist D/FirebaseApp: com.google.firebase.crash.FirebaseCrash is not linked. Skipping initialization.
01-15 10:57:58.063 18882-18882/com.thauvi_a.todolist I/FirebaseInitProvider: FirebaseApp initialization successful
01-15 10:57:58.066 18882-18882/com.thauvi_a.todolist I/InstantRun: starting instant run server: is main process
01-15 10:57:58.071 18882-18898/com.thauvi_a.todolist I/FA: App measurement is starting up, version: 11910
01-15 10:57:58.071 18882-18898/com.thauvi_a.todolist I/FA: To enable debug logging run: adb shell setprop log.tag.FA VERBOSE
01-15 10:57:58.072 18882-18898/com.thauvi_a.todolist I/FA: To enable faster debug mode event logging run:
                                                             adb shell setprop debug.firebase.analytics.app com.thauvi_a.todolist
01-15 10:57:58.072 18882-18898/com.thauvi_a.todolist D/FA: Debug-level message logging enabled
01-15 10:57:58.110 18882-18882/com.thauvi_a.todolist W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
01-15 10:57:58.190 18882-18882/com.thauvi_a.todolist D/TextView: setTypeface with style : 0
01-15 10:57:58.190 18882-18882/com.thauvi_a.todolist D/TextView: setTypeface with style : 0
01-15 10:57:58.210 18882-18882/com.thauvi_a.todolist D/POS: onStart: 
01-15 10:57:58.221 18882-18898/com.thauvi_a.todolist I/FA: Tag Manager is not found and thus will not be used
01-15 10:57:58.221 18882-18898/com.thauvi_a.todolist D/FA: Logging event (FE): screen_view(_vs), Bundle[{firebase_event_origin(_o)=auto, firebase_screen_class(_sc)=MainActivity, firebase_screen_id(_si)=8779723142852401023}]
01-15 10:57:58.222 18882-18882/com.thauvi_a.todolist D/Choreographer: init sf_choreo_doframe   debug_Level : 0x4f4cdebug_game_running : false
01-15 10:57:58.224 18882-18882/com.thauvi_a.todolist I/SemDesktopModeManager: registerListener: android.view.ViewRootImpl$3@3835360
01-15 10:57:58.224 18882-18901/com.thauvi_a.todolist I/DynamiteModule: Considering local module com.google.android.gms.firebase_database:4 and remote module com.google.android.gms.firebase_database:6
01-15 10:57:58.224 18882-18901/com.thauvi_a.todolist I/DynamiteModule: Selected remote version of com.google.android.gms.firebase_database, version >= 6
01-15 10:57:58.229 18882-18882/com.thauvi_a.todolist D/ViewRootImpl@e91f019[MainActivity]: ThreadedRenderer.create() translucent=false
01-15 10:57:58.229 18882-18901/com.thauvi_a.todolist W/System: ClassLoader referenced unknown path: 
01-15 10:57:58.232 18882-18882/com.thauvi_a.todolist D/InputTransport: Input channel constructed: fd=74
01-15 10:57:58.232 18882-18882/com.thauvi_a.todolist D/ViewRootImpl@e91f019[MainActivity]: setView = DecorView@4b0d4ea[MainActivity] touchMode=true
01-15 10:57:58.241 18882-18901/com.thauvi_a.todolist W/System: ClassLoader referenced unknown path: /data/user_de/0/com.google.android.gms/app_chimera/m/00000035/n/arm64-v8a
01-15 10:57:58.245 18882-18882/com.thauvi_a.todolist D/ViewRootImpl@e91f019[MainActivity]: dispatchAttachedToWindow
01-15 10:57:58.263 18882-18882/com.thauvi_a.todolist D/ViewRootImpl@e91f019[MainActivity]: Relayout returned: oldFrame=[0,0][0,0] newFrame=[0,0][1440,2960] result=0x27 surface={isValid=true 532786037248} surfaceGenerationChanged=true
01-15 10:57:58.263 18882-18882/com.thauvi_a.todolist D/ViewRootImpl@e91f019[MainActivity]: mHardwareRenderer.initialize() mSurface={isValid=true 532786037248} hwInitialized=true
01-15 10:57:58.272 18882-18904/com.thauvi_a.todolist D/NetworkSecurityConfig: No Network Security Config specified, using platform default
01-15 10:57:58.272 18882-18882/com.thauvi_a.todolist D/NB: getItemCount: 0
01-15 10:57:58.272 18882-18882/com.thauvi_a.todolist D/NB: getItemCount: 0
01-15 10:57:58.289 18882-18902/com.thauvi_a.todolist D/libEGL: loaded /vendor/lib64/egl/libGLES_mali.so
01-15 10:57:58.295 18882-18882/com.thauvi_a.todolist W/art: Before Android 4.1, method int android.support.v7.widget.ListViewCompat.lookForSelectablePosition(int, boolean) would have incorrectly overridden the package-private method in android.widget.ListView
01-15 10:57:58.306 18882-18902/com.thauvi_a.todolist I/OpenGLRenderer: Initialized EGL, version 1.4
01-15 10:57:58.307 18882-18902/com.thauvi_a.todolist D/OpenGLRenderer: Swap behavior 1
01-15 10:57:58.310 18882-18902/com.thauvi_a.todolist D/mali_winsys: EGLint new_window_surface(egl_winsys_display*, void*, EGLSurface, EGLConfig, egl_winsys_surface**, egl_color_buffer_format*, EGLBoolean) returns 0x3000,  [1440x2960]-format:1
01-15 10:57:58.364 18882-18882/com.thauvi_a.todolist D/ViewRootImpl@e91f019[MainActivity]: MSG_RESIZED_REPORT: frame=Rect(0, 0 - 1440, 2960) ci=Rect(0, 96 - 0, 192) vi=Rect(0, 96 - 0, 192) or=1
01-15 10:57:58.364 18882-18882/com.thauvi_a.todolist D/ViewRootImpl@e91f019[MainActivity]: MSG_WINDOW_FOCUS_CHANGED 1
01-15 10:57:58.364 18882-18882/com.thauvi_a.todolist D/ViewRootImpl@e91f019[MainActivity]: mHardwareRenderer.initializeIfNeeded()#2 mSurface={isValid=true 532786037248}
01-15 10:57:58.364 18882-18882/com.thauvi_a.todolist I/InputMethodManager: [IMM] startInputInner - mService.startInputOrWindowGainedFocus
01-15 10:57:58.367 18882-18904/com.thauvi_a.todolist D/TcpOptimizer: TcpOptimizer-ON
01-15 10:57:58.370 18882-18898/com.thauvi_a.todolist D/FA: Connected to remote service

Answer 1

您需要调用FirebaseRecyclerAdapter#startListening() 方法来启动数据监听器。最好在 Activity 的 onStart() 方法中启动监听器，然后在 onStop() 方法中移除监听器。

顺便说一下，您可以在 onCreate() 方法中移动适配器声明以获得更好的应用程序性能。

private RecyclerView mTaskList;
private DatabaseReference mDatabase;
private FirebaseRecyclerAdapter<Task, TaskViewHolder> adapter;

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

    mTaskList = findViewById(R.id.task_list);
    mTaskList.setLayoutManager(new LinearLayoutManager(this));
    mDatabase = FirebaseDatabase.getInstance().getReference().child("Tasks");

    FirebaseRecyclerOptions<Task> options = new FirebaseRecyclerOptions.Builder<Task>()
        .setQuery(mDatabase, Task.class)
        .build();

    adapter = new FirebaseRecyclerAdapter<Task, TaskViewHolder>(options) {
        @Override
        protected void onBindViewHolder(TaskViewHolder holder, int position, Task model) { }

        @Override
        public TaskViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { }
    };
    mTaskList.setAdapter(adapter);
}

下面是启动和停止数据监听器的代码

@Override
protected void onStart() {
    super.onStart();
    adapter.startListening();
}

@Override
protected void onStop() {
    super.onStop();
    adapter.stopListening();
}

希望这有帮助:)