在从Firebase数据库中提取数据时显示进度对话框

Question

我希望活动在从Firebase数据库提取数据时必须显示进度对话框，但不会显示任何内容并且会崩溃。这里是我的下面

公共类profilemain代码扩展AppCompatActivity {

private FirebaseAuth mAuth; 
private FirebaseAuth.AuthStateListener mAuthListener; 

private ProgressDialog progressDialog; 

DatabaseReference mref = 
FirebaseDatabase.getInstance().getReference("users"); 
ListView mlistview; 
ArrayList<String> arrayList=new ArrayList<>(); 
ArrayAdapter<String> arrayAdapter; 

private BottomNavigationView.OnNavigationItemSelectedListener 
mOnNavigationItemSelectedListener 
     = new BottomNavigationView.OnNavigationItemSelectedListener() { 

    @Override 
    public boolean onNavigationItemSelected(@NonNull MenuItem item) { 
     switch (item.getItemId()) { 
      case R.id.navigation_home: 
progressDialog.show(); 
       startActivity(new 
Intent(profilemain.this,profilemain.class)); 
       return true; 
      case R.id.navigation_dashboard: 
       Toast.makeText(profilemain.this,"hi 
hello",Toast.LENGTH_SHORT).show(); 
       return true; 
      case R.id.navigation_notifications: 
       Toast.makeText(profilemain.this,"hi 
hello",Toast.LENGTH_SHORT).show(); 
       return true; 
      case R.id.navigation_signout: 

       Toast.makeText(profilemain.this,"You have successfully 
Signed out",Toast.LENGTH_SHORT).show(); 
       mAuth.signOut(); 
       return true; 
     } 
     return false; 
    } 

}; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_profilemain); 
    progressDialog.setMessage("loading"); 
    progressDialog.setTitle("database is"); 

    mlistview=(ListView) findViewById(R.id.listview); 

    Firebase.setAndroidContext(this); 

    DatabaseReference ref = FirebaseDatabase.getInstance() 
      .getReference("users"); 
    //mref=new Firebase("https://stark-1dffd.firebaseio.com/users"); 
    arrayAdapter=new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,arrayList); 
    mlistview.setAdapter(arrayAdapter); 


    mref.addChildEventListener(new ChildEventListener() { 
     @Override 
     public void onChildAdded(DataSnapshot dataSnapshot, String s) { 
      String value= dataSnapshot.getValue(String.class); 

      arrayList.add(value); 
      arrayAdapter.notifyDataSetChanged(); 
      // 

      // 

     } 

     @Override 
     public void onChildChanged(DataSnapshot dataSnapshot, String s) { 

     } 

     @Override 
     public void onChildRemoved(DataSnapshot dataSnapshot) { 

     } 

     @Override 
     public void onChildMoved(DataSnapshot dataSnapshot, String s) { 

     } 

     @Override 
     public void onCancelled(DatabaseError databaseError) { 

     } 
    }); 


    BottomNavigationView navigation = (BottomNavigationView) findViewById(R.id.navigation); 
    navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener); 
    mAuth = FirebaseAuth.getInstance(); 


    mAuthListener = new FirebaseAuth.AuthStateListener() { 
     @Override 
     public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) { 
      if (firebaseAuth.getCurrentUser()==null){ 
       startActivity(new 
         Intent(profilemain.this,MainActivity.class)); 

      } 
     } 
    }; 



} 

@Override 
protected void onStart() { 
    super.onStart(); 

    mAuth.addAuthStateListener(mAuthListener); 
} 

     Process: com.food.sheenishere.stark, PID: 16408 

com.google.firebase.database.DatabaseException: Failed to convert value of type 
java.util.HashMap to String 

at com.google.android.gms.internal.zg.zzb(Unknown Source) 

at com.google.android.gms.internal.zg.zza(Unknown Source) 

at com.google.firebase.database.DataSnapshot.getValue(Unknown Source) 

at com.food.sheenishere.stark.home$1.onChildAdded(home.java:49) 

at com.google.android.gms.internal.px.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:6119) 

at java.lang.reflect.Method.invoke(Native Method) 

    at 

com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:886）

at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) 
07-15 20:49:51.645 16408-16435/com.food.sheenishere.stark W/DynamiteModule: 
Local module descriptor class for com.google.firebase.auth not found. 

Answer 1

的代码中的问题在于，您正试图在未初始化的对象上使用show（），setMessage（“loading”）和setTitle（“数据库为”）方法。

为了解决你的问题，你需要使用下面的代码：

ProgressDialog progressDialog = new ProgressDialog(this); 

这将解决你的问题是肯定的。

Answer 2

你应该初始化进度对话框..波纹状

private ProgressDialog pDialog; 

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

    pDialog = new ProgressDialog(profilemain.this); 
    pDialog.setMessage("loading.."); 
}