Question

我正在尝试在firebase快照函数中设置状态，但是我收到Cannot read property 'setState' of null错误。我不确定如何使其发挥作用。

这是我的代码：

  componentDidMount = () => {
    const dataGoalRef = dbRef.child('goals/'+this.state.uid);

    dataGoalRef.child("mainGoal").on("value", function(mainGoalKeySnapshot) {
      var favoriteMainGoal = mainGoalKeySnapshot.val();
      console.log(favoriteMainGoal);

      var queryRef = dataGoalRef.orderByKey().equalTo(favoriteMainGoal);
      queryRef.on("value", snap => {
        this.setState({
          dataGoal: snap.val(),
        });
      });
    });
  }

我该怎么办？

Answer 1

我刚想通了。我没有约束第一种方法。所以解决方案是：

  componentDidMount = () => {
    const dataGoalRef = dbRef.child('goals/'+this.state.uid);

    dataGoalRef.child("mainGoal").on("value", (mainGoalKeySnapshot) => {
      var favoriteMainGoal = mainGoalKeySnapshot.val();
      console.log(favoriteMainGoal);

      var queryRef = dataGoalRef.orderByKey().equalTo(favoriteMainGoal);
      queryRef.on("value", snap => {
        this.setState({
          dataGoal: snap.val(),
        });
      });
    });
  }

Answer 2

尝试使用箭头函数代替普通函数声明进行dataGoalRef.child("mainGoal").on("value", function(mainGoalKeySnapshot){})中传递的回调

更新代码

dataGoalRef.child("mainGoal").on("value", (mainGoalKeySnapshot) => {
 ....
 ....
});

React和Firebase - 无法设置状态

2 个答案: