this.setState() on react native 不使用文本输入

Question

I'm trying to print the user's info from firebase into placeholder of TextInput but when i try to set the info it isn't represented and node gives me a message:

Error:

 Please update the following components: ProfileContent
 LOG  user logged
 LOG  -----O myemail.com
 LOG  -----O myname
 LOG  -----O mylastname
 LOG  -----O adriangc24
 WARN  Possible Unhandled Promise Rejection (id: 1):
TypeError: undefined is not an object (evaluating '_this2.setState')

My constructor:

constructor(props) {
    super(props);
    this.state = {
      name: "",
      lastname: "",
      displayname: "",
      email: "",
    };
  }
  state = {
    name: "Nombre",
    lastname: "Apellidos",
    displayname: "Nombre de usuario",
    email: "Correo electrónico",
  };

TextInput example:

    <TextInput
                      autoCapitalize="sentences"
                      style={styles.userInput}
                      placeholder={this.state.lastname}
                      ref={"lastnamesInput"}
                    />

My method for get the user's data from firebase:

function getUserData() {
  firebase.auth().onAuthStateChanged(function (user) {
    if (user) {
      console.log("user logged");
      var usuario = firebase.database().ref("/users/" + user.uid);
      usuario.once("value").then((snapshot) => {
        var usr = snapshot.val();
        console.log("-----O " + usr.email);
        console.log("-----O " + usr.name);
        console.log("-----O " + usr.lastname);
        console.log("-----O " + usr.displayname);

        this.setState(
          {
            name: usr.name,
            lastname: usr.lastname,
            displayname: usr.displayname,
            email: usr.email,
          },
          () => {
            console.log("///////////////////////////////////////");
            console.log("XXXXXX " + this.state.email);
          }
        );
      });
    } else {
      console.log("user not logged");
    }
  });
}

Answer 1

It's the scope issue, due to function (user) { you have lost the scope of this , solution to this is use fat arrow function .

Change this:

  firebase.auth().onAuthStateChanged(function (user) {

To

  firebase.auth().onAuthStateChanged((user) => {