小编chr*_*bot的帖子

snapshot.forEach(function(childSnapshot) {
  groupRef.child(childSnapshot.key).once("value", (snap) => {
    this.setState.bind({
      expenses: this.state.expenses.concat(snap.val()),
    });
  })
})

我得到的错误是

undefined is not an object (evaluating '_this2.setState')

国家已按以下方式宣布

constructor(props) {
  super (props);
  this.state = {
    expenses: [],
  };
}