firebase.auth().onAuthStateChanged((user) => {
      if (user) {
        firebase.database().ref('Usuarios').on('value', (snapshot) => {
          let state = this.state;
          state.list = [];

          snapshot.forEach((childItem) => {
            state.list.push({
              key: childItem.key,
              titulo: childItem.val().titulo,
              nome: childItem.val().nome,
            });
          });
          this.setState(state);
        });
      }
    });