Question

我正在尝试创建一个名为sendRegisterUserMessage（）的方法，如果数据库中尚不存在用户，则该方法会将User对象发送到Firebase数据库。出于某种原因，尽管使用侦听器在数据库中找到了对象，但该方法始终返回false。

无论如何我在onCreate（）的MainActiviy中调用了这个方法：

MessageSenderHandler.getInstance().sendRegisterUserMessage();

在我的MessageSenderHandler类中：

//Checks if user is Registered- if not it sends a RegisterUser message
public void sendRegisterUserMessage() {
    System.out.println("registered: " +DatabaseManager.getInstance().isCurrentUserRegistered()); //This prints false no matter what
    if (DatabaseManager.getInstance().isCurrentUserRegistered() == false) {
        FirebaseDatabase.getInstance().getReference().child(MessageTypes.REGISTER_USER_MESSAGE).child(
                CurrentUser.getInstance().getUserId())
                .setValue(
                        new RegisterUserMessage()
                );
    }
}

然后这是我的DatabaseManager类中的isCurrentUserRegistered（）方法

public boolean isCurrentUserRegistered() {
    Query query = databaseReference.child("/" + MessageTypes.REGISTER_USER_MESSAGE + "/" + CurrentUser.getInstance().getUserId());
    query.addValueEventListener(isUserRegisteredDataListener);
    System.out.println("REGISTERED:" + isUserRegisteredDataListener.isUserRegisterd()); //This also prints false no matter what
    return isUserRegisteredDataListener.isUserRegisterd();
}

这是我的IsUerRegisteredDataListener

public class IsUserRegisteredDataListener implements ValueEventListener {

static boolean exists;

private static IsUserRegisteredDataListener isUserRegisteredDataListener;
public IsUserRegisteredDataListener() {
    isUserRegisteredDataListener = this;
}
public static IsUserRegisteredDataListener getInstance() {
    if (isUserRegisteredDataListener == null) {
        isUserRegisteredDataListener = new IsUserRegisteredDataListener();
    }
    return isUserRegisteredDataListener;
}
@Override
public void onDataChange(DataSnapshot dataSnapshot) {

        this.exists = dataSnapshot.exists(); 
        System.out.println("EXISTS" + exists)); //This prints true
}

@Override
public void onCancelled(DatabaseError databaseError) {

}

public boolean isUserRegisterd() {
    return exists;
}

}

我不明白为什么前两个方法打印为FALSE但是实际数据监听器的方法在侦听器中打印为TRUE

Answer 1

public boolean isCurrentUserRegistered() {
    Query query = databaseReference.child("/" + MessageTypes.REGISTER_USER_MESSAGE + "/" + CurrentUser.getInstance().getUserId());
    query.addValueEventListener(isUserRegisteredDataListener);
    System.out.println("REGISTERED:" + isUserRegisteredDataListener.isUserRegisterd()); //This also prints false no matter what
    return isUserRegisteredDataListener.isUserRegisterd();
}

在此方法中，您必须等待firebase结果获得isUserRegistered。所以你的IsUserRegisteredDataListener课程无法按你的意愿工作。

您能否显示初始化isUserRegisteredDataListener字段的位置？

如何使用Firebase查询返回布尔值？

1 个答案: