为什么会出现此错误：java.lang.IllegalStateException：调用 commit() 后无法再使用写入批处理

Question

下面的代码我试图删除一个会员，应该删除一个会员及其详细信息和所有费用记录。

 public void deleteMember(Member member) {
    final WriteBatch batch = FirebaseFirestore.getInstance().batch();
    DocumentReference memberDoc = getMemberReference().document(member.getMemberId());
    batch.delete(memberDoc);
             getFeeReference().whereEqualTo("id", member.getMemberId())
            .get()
            .addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
                @Override
                public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
                    for(QueryDocumentSnapshot snapshot : queryDocumentSnapshots){
                        batch.delete(snapshot.getReference()); // this is the line of error
                    }
                }
            });
    batch.commit();
    getMemberImagesReference().child(member.getMemberId() + "t.jpg").delete();
    getMemberImagesReference().child(member.getMemberId() + "f.jpg").delete();
}

但我收到以下错误

 2020-04-10 22:57:33.462 29454-29454/com.abhinav.chauhan.gymdatamanager D/AndroidRuntime: Shutting 
 down VM
 2020-04-10 22:57:33.464 29454-29454/com.abhinav.chauhan.gymdatamanager E/AndroidRuntime: FATAL 
 EXCEPTION: main
 Process: com.abhinav.chauhan.gymdatamanager, PID: 29454
 java.lang.IllegalStateException: A write batch can no longer be used after commit() has been called.
    at com.google.firebase.firestore.WriteBatch.verifyNotCommitted(com.google.firebase:firebase- 
     firestore@@21.4.2:202)
    at com.google.firebase.firestore.WriteBatch.delete(com.google.firebase:firebase- 
    firestore@@21.4.2:179)
    at 
    com.abhinav.chauhan.gymdatamanager.database.FireBaseHandler$1.onSuccess(FireBaseHandler.java:110)
    at    
    com.abhinav.chauhan.gymdatamanager.database.FireBaseHandler$1.onSuccess(FireBaseHandler.java:106)
    at com.google.android.gms.tasks.zzn.run(Unknown Source:4)
    at android.os.Handler.handleCallback(Handler.java:808)
    at android.os.Handler.dispatchMessage(Handler.java:101)
    at android.os.Looper.loop(Looper.java:166)
    at android.app.ActivityThread.main(ActivityThread.java:7425)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921)

Answer 1

get()是异步的，并在查询完成之前立即返回。之后您的代码将继续提交批处理，并在其中进行一次删除。一段时间后，在 get() 完成后，您的代码会在完成后尝试将另一个删除添加到批处理中。这就是您收到错误的原因 - 调用 后无法再次修改批次commit()。

也许您应该等到回调被调用后再添加所有要修改的文档并调用 commit()，以确保这commit()是批处理中调用的最后一个方法。