从valueEventListenerjava返回值

与所有异步操作一样,我经常以回调方式执行此操作.

您的解决方案可以这样工作:

创建一个简单的回调接口(我在几乎每个应用程序中使用的库中都有我的)

public interface SimpleCallback {
    void callback(Object data);
}

// You could do it as well generic, that's what I do in my lib:
public interface SimpleCallback {
    void callback(T data);
}

然后重新设计方法的签名,如下所示:

private void checkAnswerSubmission(@NonNull SimpleCallback finishedCallback) {

    DatabaseReference answerDatabase = FirebaseDatabase.getInstance().getReference().child("userPuzzleHistory").child(uid);
    answerDatabase.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            // This will simple call your callback containing a boolean true/false
            finishedCallback.callback(dataSnapshot.hasChild(String.valueOf(imagename)));
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
}

你这称之为:

checkAnswerSubmission(new SimpleCallback() {
   @Override
   void callback(boolean data) {
       if (data) {
          // true was returned
       } else {
          // false was returned
       }
   }
});