未定义不是this.setState函数 [英] Undefined is not a function this.setState

问题描述

我创建了一个简单的登录页面，一旦按下该按钮，它将执行以下功能:

I created a simple login page, which, once the button is pressed, executes this function :

login = (email, password, navigate) => {
  this.setState({ loginButtonPressed: true });
  firebase
    .auth()
    .signInWithEmailAndPassword(email, password)
    .then(function(user) {
      navigate('Profile');
    })
    .catch(function(error) {
      this.setState({ loginButtonPressed: false });
      Alert.alert(error.toString());
    });
};

一旦调用，它将执行"this.setState({loginButtonPressed:true})"，因为按钮会改变形状(标记为已按下).但是出现以下错误:未定义不是this.setState 函数.

Once called, it executes "this.setState({ loginButtonPressed: true })" since the button changes shape (it is marked as pressed). But I get the following error: Undefined is not a function this.setState.

如何解决?感谢您的帮助.

How can this be fixed? Thanks for your help.

推荐答案

问题出在:

.catch(function(error) {
  this.setState({ loginButtonPressed: false });
  Alert.alert(error.toString());
});

您创建一个匿名函数，其中 this 将引用该匿名函数(对象)，而不是React对象.

you create an anonymous function where this will reference this anonymous function (Object), not a React Object.

我看到您可以使用箭头功能，所以请像这样修复它:

I see you can use arrow functions, so fix it like:

.catch((error) => {
  this.setState({ loginButtonPressed: false });
  Alert.alert(error.toString());
});

使用箭头功能此将引用使用它的上下文.

With arrow function this will reference context in which it is used.

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