Firebase处理disconect到数据库 [英] Firebase Handling disconect to database

问题描述

我不确定它是disconect或DatabaseErrors事件。首先，我在开始在Firebase上加载数据时有一个对话框显示，然后我想在两种情况下关闭对话框：

1. 有互联网：加载数据成功，并在onDataChange dissmiss对话框。




2. 没有互联网连接或应用程序启动时快速关闭WiFi。在第二种情况下，我认为它会调用onCancelled，在这种方法中，我将关闭对话框。但实际上，这不是要求取消。
   
   

   那么，如何在第二种情况下解除对话。这里是我的代码

   
   
   pre $ private $ getCategory（）{
   mDatabase = FirebaseDatabase.getInstance（）。getReference（）;
   mDatabase.child（ReferenceToFirebase.CHILD_CATEGORIES）
   .addListenerForSingleValueEvent（new ValueEventListener（）{
   @Override
   public void onDataChange（DataSnapshot dataSnapshot）{
   // do something
   
   //然后关闭对话框
   mDialog.dismiss（）;
   
   $ b @Override $ b $ public void onCancelled（DatabaseError databaseError）{
   mDialog.dismiss（）;
   }
   }）;
   
   $ / code>

   
   

   解决方案

   onCancelled（）在服务器拒绝侦听器时调用，通常当用户没有访问数据的权限时。

   
   
   

   如果您没有与Firebase数据库的连接，可能需要阻止附加侦听器。为此，您可以收听。 info / connected ，只有当侦听器是真实的时候才附加监听器。
   
   

     mDatabase = 。FirebaseDatabase.getInstance（）getReference（）; 
    DatabaseReference connectedRef = mDatabase.child（。info / connected）; 
    connectedRef.addValueEventListener（new ValueEventListener（）{
    @Override 
    public void onDataChange（DataSnapshot snapshot）{
    boolean connected = snapshot.getValue（Boolean.class）; $ b $如果（连接）{
    mDatabase.child（ReferenceToFirebase.CHILD_CATEGORIES）
    .addListenerForSingleValueEvent（new ValueEventListener（）{
    @Override 
    public void onDataChange（DataSnapshot dataSnapshot）{
    //执行某些操作
    
    //然后关闭对话框
    mDialog.dismiss（）; 
   } 
    
    @Override 
    public void System.err.println（Listener was canceled）; 
    mDialog.dismiss（）; 
   } 
   }）; 
   }其他{
    System.out.println（未连接）; 
    mDialog.dismiss（ ）; 
    
    
    $ b @Override 
    public void onCancelled（DatabaseError error）{
    System.err.println（Listener was canceled）; 
   } 
   }）; 
     

   
   

   I'm not sure it's disconect or DatabaseErrors event. First I have a dialog show when start loading data on Firebase, and then I want to dismiss that dialog in two case :

   1. have internet: load data success, and I dissmiss dialog in onDataChange.

   2. no internet connection or turn off wifi quickly when app start.

   In second case, I think It's will call onCancelled, and in that method, I will dismiss dialog. But in real, it's not call onCancelled.

   So, how I can dissmiss dialog on second case. Here's my code

   private void getCategory() {
       mDatabase = FirebaseDatabase.getInstance().getReference();
       mDatabase.child(ReferenceToFirebase.CHILD_CATEGORIES)
               .addListenerForSingleValueEvent(new ValueEventListener() {
                   @Override
                   public void onDataChange(DataSnapshot dataSnapshot) {
                       //do something
   
                       //then dismiss dialog
                       mDialog.dismiss();
                   }
   
                   @Override
                   public void onCancelled(DatabaseError databaseError) {
                       mDialog.dismiss();
                   }
               });
   }
   

   解决方案

   onCancelled() is called when the server rejects the listener, typically when the user doesn't have permission to access the data.

   You'll probably want to prevent attaching the listener if you don't have a connection to the Firebase Database. For that you can listen to .info/connected and only attach the listener when that is true.

   mDatabase = FirebaseDatabase.getInstance().getReference();
   DatabaseReference connectedRef = mDatabase.child(".info/connected");
   connectedRef.addValueEventListener(new ValueEventListener() {
     @Override
     public void onDataChange(DataSnapshot snapshot) {
       boolean connected = snapshot.getValue(Boolean.class);
       if (connected) {
           mDatabase.child(ReferenceToFirebase.CHILD_CATEGORIES)
               .addListenerForSingleValueEvent(new ValueEventListener() {
                   @Override
                   public void onDataChange(DataSnapshot dataSnapshot) {
                       //do something
   
                       //then dismiss dialog
                       mDialog.dismiss();
                   }
   
                   @Override
                   public void onCancelled(DatabaseError databaseError) {
                       System.err.println("Listener was cancelled");
                       mDialog.dismiss();
                   }
           });
       } else {
         System.out.println("not connected");
         mDialog.dismiss();
       }
     }
   
     @Override
     public void onCancelled(DatabaseError error) {
       System.err.println("Listener was cancelled");
     }
   });
   

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