如何同步读取Firebase实时数据库值? [英] How to read Firebase realtime database value synchronously?

问题描述

我正在使用Firebase实时数据库，据我所知，您必须使用

I'm using firebase realtime database and as far I know, you have to use the

 DatabaseReference.addValueEventListener

从firebase数据库中读取一个值.

to read a value from the firebase database.

此处addValueEventListener在默认情况下是异步的.我需要同步阅读.对于FireBase存储，对于上载文件时的相同问题，我可以使用

Here addValueEventListener is asynchronous by default. I need to read it synchronously. For FireBase storage, for the same issue while uploading files, I could make the process synchronous by using

     UploadTask.TaskSnapshot await = Tasks.await(uploadTask);

代替使用

     uploadTask.addOnCompleteListener(new OnCompleteListener<UploadTask.TaskSnapshot>() {
                                                    @Override
                                                    public void onComplete(@NonNull Task<UploadTask.TaskSnapshot> task) {

                                                    }
                                                })          

是否有与上述类似的addValueEventListener同步替代方案?

Is there any similar synchronous alternative for addValueEventListener like shown above?

推荐答案

尝试从异步的API同步返回值，这不是一个好主意.但是，如果您的块已经与主线程异步-您可以使用CountDownLatch和await回调响应.

Trying to return a value synchronously from an API that's asynchronous, it's not a good idea. But if your block is already asynchronous with main thread - you can use CountDownLatch and await callback response.

示例:

CountDownLatch latch = new CountDownLatch(1);
uploadTask.addOnCompleteListener(new OnCompleteListener<UploadTask.TaskSnapshot>(){
       @Override
       public void onComplete(@NonNull Task<UploadTask.TaskSnapshot> task) {
            //Handle response
            latch.countDown();
       }
});
latch.await();

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