Reactでログイン機能を実装する。(Step4: ログインAPIのレスポンスに応じて、画面の出しわけをする。)

[前回記事](https://qiita.com/kouji0705/items/7c9f42ea7fb1db1241b5)の続きです。

ReactのAPIレスポンスの結果に応じて、表示する画面を切り替える。
※本記事ではValidationチェックが通るかのみで、認証のステータスは判断している。

### 成果物
ログイン画面
![スクリーンショット 2022-08-11 22.01.36.png](https://qiita-image-store.s3.ap-northeast-1.amazonaws.com/0/599049/8379281e-cd30-86d7-bf38-47d86f5dd0c5.png)

ログイン成功
![スクリーンショット 2022-08-11 22.02.05.png](https://qiita-image-store.s3.ap-northeast-1.amazonaws.com/0/599049/09c197a9-aa4a-d84a-eb20-b816dea3ccc6.png)

ログイン失敗
![スクリーンショット 2022-08-11 22.02.27.png](https://qiita-image-store.s3.ap-northeast-1.amazonaws.com/0/599049/f7a6d912-8fec-8fbf-564c-173a4bc71742.png)

### 環境情報
```ディレクトリ構成
~/develop/react/react_study/login$ tree -I node_modules     
.
├── README.md
├── package.json
├── public
│   ├── favicon.ico
│   ├── index.html
│   ├── logo192.png
│   ├── logo512.png
│   ├── manifest.json
│   └── robots.txt
├── src
│   ├── App.tsx
│   ├── components
│   │   ├── Header.tsx
│   │   └── Login.tsx
│   ├── index.tsx
│   ├── pages
│   │   ├── FailedLogin.tsx
│   │   └── Home.tsx
│   ├── router
│   │   └── Router.tsx
│   └── types
│       └── User.ts
├── tsconfig.json
└── yarn.lock
```

```json:package.json
{
  "name": "login",
  "version": "0.1.0",
  "private": true,
  "dependencies": {
    "@emotion/react": "^11.10.0",
    "@emotion/styled": "^11.10.0",
    "@mui/icons-material": "^5.8.4",
    "@mui/material": "^5.10.0",
    "@testing-library/jest-dom": "^5.14.1",
    "@testing-library/react": "^13.0.0",
    "@testing-library/user-event": "^13.2.1",
    "@types/jest": "^27.0.1",
    "@types/node": "^16.7.13",
    "@types/react": "^18.0.0",
    "@types/react-dom": "^18.0.0",
    "axios": "^0.27.2",
    "react": "^18.2.0",
    "react-dom": "^18.2.0",
    "react-query": "^4.0.0",
    "react-router-dom": "^6.3.0",
    "react-scripts": "5.0.1",
    "typescript": "^4.4.2",
    "web-vitals": "^2.1.0"
  },
  "scripts": {
    "start": "react-scripts start",
    "build": "react-scripts build",
    "test": "react-scripts test",
    "eject": "react-scripts eject"
  },
  "eslintConfig": {
    "extends": [
      "react-app",
      "react-app/jest"
    ]
  },
  "browserslist": {
    "production": [
      ">0.2%",
      "not dead",
      "not op_mini all"
    ],
    "development": [
      "last 1 chrome version",
      "last 1 firefox version",
      "last 1 safari version"
    ]
  }
}
```

### Hands-on
```tsx:src/index.tsx
import React from "react";
import ReactDOM from "react-dom/client";
import { BrowserRouter } from "react-router-dom";
import { Router } from "./router/Router";

const root = ReactDOM.createRoot(
  document.getElementById("root") as HTMLElement
);
root.render(
  <React.StrictMode>
    <BrowserRouter>
      <Router />
    </BrowserRouter>
  </React.StrictMode>
);
```

```tsx:src/App.tsx
import CssBaseline from "@mui/material/CssBaseline";
import { ThemeProvider, createTheme } from "@mui/material/styles";
import Header from "./components/Header";
import { Login } from "./components/Login";

function App() {
  const theme = createTheme({
    palette: {
      mode: "light",
    },
  });

  return (
    <ThemeProvider theme={theme}>
      <CssBaseline />
      <Header />
      <Login />
    </ThemeProvider>
  );
}

export default App;
```

```tsx:src/components/Header.tsx
import AppBar from "@mui/material/AppBar";
import Box from "@mui/material/Box";
import Toolbar from "@mui/material/Toolbar";
import Typography from "@mui/material/Typography";

export default function Header() {
  return (
    <Box sx={{ flexGrow: 1 }}>
      <AppBar position="static">
        <Toolbar>
          <Typography variant="h6" component="div" sx={{ flexGrow: 1 }}>
            ヘッダー
          </Typography>
        </Toolbar>
      </AppBar>
    </Box>
  );
}
```

```tsx:src/components/Login.tsx
import {
  Box,
  Button,
  Card,
  CardActions,
  CardContent,
  CardHeader,
  TextField,
} from "@mui/material";
import axios from "axios";
import { memo, useState } from "react";
import { User } from "../types/User";
import { useNavigate } from "react-router-dom";

export const Login = memo(() => {
  const [userId, setUserId] = useState("");
  const [password, setPassword] = useState("");
  const navigate = useNavigate();

  const cardStyle = {
    display: "block",
    transitionDuration: "0.3s",
    height: "450px",
    width: "400px",
    variant: "outlined",
  };

  const onClickLogin = async () => {
    const authStatus = await axios
      .post<User>("http://localhost:1323/api/login", {
        user_id: userId,
        password,
      })
      .then(() => navigate("/home"))
      .catch((error) => {
        navigate("/fail_login");
      });
    console.log("authStatus: ", authStatus);
  };

  return (
    <Box
      display="flex"
      alignItems="center"
      justifyContent="center"
      padding={20}
    >
      <Card style={cardStyle}>
        <CardHeader title="ログインページ" />
        <CardContent>
          <div>
            <TextField
              fullWidth
              id="username"
              type="email"
              label="Username"
              placeholder="Username"
              margin="normal"
              onChange={(e) => setUserId(e.target.value)}
            />
            <TextField
              fullWidth
              id="password"
              type="password"
              label="Password"
              placeholder="Password"
              margin="normal"
              onChange={(e) => setPassword(e.target.value)}
            />
          </div>
        </CardContent>
        <CardActions>
          <Button
            variant="contained"
            size="large"
            color="secondary"
            onClick={onClickLogin}
          >
            Login
          </Button>
        </CardActions>
      </Card>
    </Box>
  );
});
```

```tsx:src/pages/FailedLogin.tsx
import { memo } from "react";

export const FailedLogin = memo(() => {
  return <p>ログイン失敗です。</p>;
});
```

```tsx:src/pages/Home.tsx
import { memo } from "react";

export const Home = memo(() => {
  return <p>Homeページです</p>;
});
```

```tsx:src/router/Router.tsx
import { Route, Routes } from "react-router-dom";
import Header from "../components/Header";
import { Login } from "../components/Login";
import { FailedLogin } from "../pages/FailedLogin";
import { Home } from "../pages/Home";

export const Router = () => {
  return (
    <Routes>
      <Route
        path="/login"
        element={
          <>
            <Header />
            <Login />
          </>
        }
      />
      <Route path="/home" element={<Home />} />
      <Route path="/fail_login" element={<FailedLogin />} />
    </Routes>
  );
};
```

```ts:src/types/User.ts
export interface User {
  user_id: string;
  password: string;
}
```
→はい、これで完成！！！