How do i solve this Hook error in React Native?

Question

Im Trying to make this app as a Project because i just learned React Native and i've gotten this far without problems but i keep getting this Hook problem:

Uncaught Error: Invalid hook call. Hooks can only be called inside of the body of a function component. This could happen for one of the following reasons:

1. You might have mismatching versions of React and the renderer (such as React DOM)
2. You might be breaking the Rules of Hooks
3. You might have more than one copy of React in the same app See https://reactjs.org/link/invalid-hook-call for tips about how to debug and fix this problem. at resolveDispatcher (react.development.js:1476:1) at useState (react.development.js:1507:1) at Module../App.js (App.js:11:1) at webpack_require (bootstrap:789:1) at fn (bootstrap:100:1) at Module../node_modules/expo/AppEntry.js (AppEntry.js:1:1) at webpack_require (bootstrap:789:1) at fn (bootstrap:100:1) at Object.1 (index.js:18:1) at webpack_require (bootstrap:789:1) at bootstrap:856:1 at bootstrap:856:1

React Native:

import React, { useState } from "react";
import { StyleSheet, Text, View, TextInput, Button } from "react-native";
import { createStackNavigator } from "@react-navigation/stack";
import { NavigationContainer } from "@react-navigation/native";
import { createBottomTabNavigator } from "@react-navigation/bottom-tabs";

const Stack = createStackNavigator();
const Tab = createBottomTabNavigator();

const [password, setPassword] = useState("");
const [username, setUsername] = useState("");
const [hasUser, setUser] = useState(false);
const [error, setError] = useState("");

export const AppNavigator = () => {
  const check = hasUser;
  if (check == true) {
    return (
      <Tab.Navigator>
        <Tab.Screen name="Feed" component={FeedScreen} />
      </Tab.Navigator>
    );
  }
  if (check == false) {
    return (
      <Stack.Navigator>
        <Stack.Screen name="Login" component={LoginScreen} />
      </Stack.Navigator>
    );
  }
};
const LoginScreen = () => {
  <View style={styles.container}>
    <Text style={styles.titleLogin}>VKAW</Text>
    <View style={styles.inputs}>
      <Text style={{ color: "red" }}>{error}</Text>
      <TextInput
        placeholder="Benutzername"
        onChangeText={(usernameSet) => setUsername(usernameSet)}
        value={username}
      ></TextInput>
      <TextInput
        placeholder="Password"
        secureTextEntry={true}
        onChangeText={(passwordSet) => setPassword(passwordSet)}
        value={password}
      ></TextInput>
    </View>
    <Button title="Login" color="#ff8800" onPress={login()} />
    <StatusBar style="auto" />
  </View>;
};

const FeedScreen = () => {
  <View>
    <Text>Feed</Text>
  </View>;
};

const login = () => {
  const usernameCheck = username;
  const passwordCheck = password;
  if (usernameCheck == "test" && passwordCheck == "test") {
    setUser(true);
  } else {
    setError("Passwort oder Benutzername Falsch!");
  }
};

const App = () => {
  return (
    <NavigationContainer>
      <AppNavigator />
    </NavigationContainer>
  );
};

export default App();

const styles = StyleSheet.create({
  container: {
    flex: 1,
    backgroundColor: "#fff",
    alignItems: "center",
    justifyContent: "center",
  },
  titleLogin: {
    fontSize: 30,
    fontWeight: "bold",
    color: "#ff8800",
    paddingBottom: 50,
  },
  inputs: {
    display: "flex",
    width: 150,
    paddingBottom: 50,
    justifyContent: "center",
    alignItems: "center",
  },
});

Answer 1

All the useState calls need to be inside a React component, which can be AppNavigator in your case:

const Stack = createStackNavigator();
const Tab = createBottomTabNavigator();

export const AppNavigator = () => {
  const [password, setPassword] = useState("");
  const [username, setUsername] = useState("");
  const [hasUser, setUser] = useState(false);
  const [error, setError] = useState("");

  ///....
};

See Rules of Hooks to learn more.

Answer 2

The error is clear, you can use hooks only inside of the body of a function component.

So all this code:

const [password, setPassword] = useState("");
const [username, setUsername] = useState("");
const [hasUser, setUser] = useState(false);
const [error, setError] = useState("");

should be moved inside App component. That's it