如何从 android 的 firebase 中检索 List 对象 [英] How to Retrieve a List object from the firebase in android

问题描述

我无法从 Firebase 检索列表.我存储它没有问题，但是一旦我尝试将 dataSnapshot.getValue() 转换为 ArrayList 我的应用程序就会崩溃，并给出一个异常:

I am having trouble retrieving a List from the Firebase. I have no trouble storing it, but as soon as I try to cast dataSnapshot.getValue() to ArrayList my app crashes, giving an exception:

HashMap 无法转换为 ArrayList

HashMap cannot be casted to ArrayList

但是当我尝试将其转换为 HashMap 时，它也会崩溃，并给出异常:

But when I tried to cast it to a HashMap, it also crashes, giving exception:

ArrayList 无法转换为 hashmap

ArrayList can't be casted to hashmap

需要帮助请！这是造成问题的代码:

Need help please! Here is the code that is creating the problem:

Fire.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        List<TaskDes> td = (ArrayList<TaskDes>) dataSnapshot.getValue()
        notifyDataSetChanged();
    }

    @Override
    public void onCancelled(FirebaseError firebaseError) {

    }
});

我想将 Firebase 中的所有数据作为一个列表进行检索.TaskDes 类包含三个字段:

I want to retrieve all the data in the Firebase as one List. The class TaskDes contains three fields:

class TaskDes { // definition
    boolean done
    String taskDescription
    String taskTitle
}

推荐答案

您需要创建一个 GenericTypeIndicator 对象作为 DataSnapshot.getValue() 参数传递.

You need to create a GenericTypeIndicator object to pass as DataSnapshot.getValue() parameter.

代码:

GenericTypeIndicator<List<String>> t = new GenericTypeIndicator<List<String>>() {};

List<String> yourStringArray = dataSnapshot.getValue(t);

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