react-native-webview/docs/Guide.md

# React Native WebView Guide

This document walks you through the most common use cases for React Native WebView. It doesn't cover [the full API](Reference.md), but after reading it and looking at the sample code snippets you should have a good sense for how the WebView works and common patterns for using the WebView.

_This guide is currently a work in progress._

## Guide Index

- [Basic Inline HTML](Guide.md#basic-inline-html)
- [Basic URL Source](Guide.md#basic-url-source)
- [Controlling navigation state changes](Guide.md#controlling-navigation-state-changes)
- [Add support for File Upload](Guide.md#add-support-for-file-upload)
- [Add support for File Download](Guide.md#add-support-for-file-download)
- [Communicating between JS and Native](Guide.md#communicating-between-js-and-native)

### Basic inline HTML

The simplest way to use the WebView is to simply pipe in the HTML you want to display. Note that setting an `html` source requires the [originWhiteList](Reference.md#originWhiteList) property to be set to `['*']`.

```js
import React, { Component } from 'react';
import { WebView } from 'react-native-webview';

class MyInlineWeb extends Component {
  render() {
    return (
      <WebView
        originWhitelist={['*']}
        source={{ html: '<h1>This is a static HTML source!</h1>' }}
      />
    );
  }
}
```

Passing a new static html source will cause the WebView to rerender.

### Basic URL Source

This is the most common use-case for WebView.

```js
import React, { Component } from 'react';
import { WebView } from 'react-native-webview';

class MyWeb extends Component {
  render() {
    return (
      <WebView
        source={{uri: 'https://facebook.github.io/react-native/'}}
      />
    );
  }
}
```

### Controlling navigation state changes

Sometimes you want to intercept a user tapping on a link in your webview and do something different than navigating there in the webview. Here's some example code on how you might do that using the `onNavigationStateChange` function.

```js
import React, { Component } from 'react';
import { WebView } from 'react-native-webview';

class MyWeb extends Component {
  webview = null;

  render() {
    return (
      <WebView
        ref={ref => (this.webview = ref)}
        source={{uri: 'https://facebook.github.io/react-native/'}}
        onNavigationStateChange={this.handleWebViewNavigationStateChange}
      />
    );
  }

  handleWebViewNavigationStateChange = newNavState => {
    // newNavState looks something like this:
    // {
    //   url?: string;
    //   title?: string;
    //   loading?: boolean;
    //   canGoBack?: boolean;
    //   canGoForward?: boolean;
    // }
    const { url } = newNavState;
    if (!url) return

    // handle certain doctypes
    if (url.includes('.pdf')) {
      this.webview.stopLoading();
      // open a modal with the PDF viewer
    }

    // one way to handle a successful form submit is via query strings
    if (url.includes('?message=success')) {
      this.webview.stopLoading();
      // maybe close this view?
    }

    // one way to handle errors is via query string
    if (url.includes('?errors=true')) {
      this.webview.stopLoading();
    }

    // redirect somewhere else
    if (url.includes('google.com')) {
      const newURL = 'https://facebook.github.io/react-native/';
      const redirectTo = 'window.location = "' + newURL + '"';
      this.webview.injectJavaScript(redirectTo);
    }
  }
}
```

### Add support for File Upload

##### iOS

For iOS, all you need to do is specify the permissions in your `ios/[project]/Info.plist` file:

Photo capture:
```
<key>NSCameraUsageDescription</key>
<string>Take pictures for certain activities</string>
```

Gallery selection:
```
<key>NSPhotoLibraryUsageDescription</key>
<string>Select pictures for certain activities</string>
```

Video recording:
```
<key>NSMicrophoneUsageDescription</key>
<string>Need microphone access for recording videos</string>
```

##### Android

Add permission in AndroidManifest.xml:
```xml
<manifest ...>
  ......

  <!-- this is required only for Android 4.1-5.1 (api 16-22)  -->
  <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

  ......
</manifest>
```

##### Check for File Upload support, with `static isFileUploadSupported()`

File Upload using `<input type="file" />` is not supported for Android 4.4 KitKat (see [details](https://github.com/delight-im/Android-AdvancedWebView/issues/4#issuecomment-70372146)):

```
import { WebView } from "react-native-webview";

WebView.isFileUploadSupported().then(res => {
  if (res === true) {
    // file upload is supported
  } else {
    // not file upload support
  }
});

```

### Add support for File Download

##### iOS

For iOS, all you need to do is specify the permissions in your `ios/[project]/Info.plist` file:

Save to gallery:
```
<key>NSPhotoLibraryAddUsageDescription</key>
<string>Save pictures for certain activities.</string>
```

##### Android

Add permission in AndroidManifest.xml:

```xml
<manifest ...>
  ......

  <!-- this is required to save files on Android  -->
  <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

  ......
</manifest>
```

### Communicating between JS and Native

You will often find yourself wanting to send messages to the web pages loaded by your webviews and also receiving messages back from those web pages.

To accomplish this, React Native WebView exposes three different options:

1. React Native -> Web: The `injectedJavaScript` prop
2. React Native -> Web: The `injectJavaScript` method
3. Web -> React Native: The `postMessage` method and `onMessage` prop

#### The `injectedJavaScript` prop

This is a script that runs immediately after the web page loads for the first time. It only runs once, even if the page is reloaded or navigated away.

```jsx
import React, { Component } from "react";
import { View } from "react-native";
import { WebView } from "react-native-webview";

export default class App extends Component {
  render() {
    const runFirst = `
      document.body.style.backgroundColor = 'red';
      setTimeout(function() { window.alert('hi') }, 2000);
      true; // note: this is required, or you'll sometimes get silent failures
    `;
    return (
      <View style={{ flex: 1 }}>
        <WebView
          source={{
            uri:
              "https://github.com/react-native-community/react-native-webview"
          }}
          injectedJavaScript={runFirst}
        />
      </View>
    );
  }
}
```

This runs the JavaScript in the `runFirst` string once the page is loaded. In this case, you can see that both the body style was changed to red and the alert showed up after 2 seconds.

<img alt="screenshot of Github repo" width="200" src="https://user-images.githubusercontent.com/1479215/53609254-e5dc9c00-3b7a-11e9-9118-bc4e520ce6ca.png" />

*Under the hood*

> On iOS, `injectedJavaScript` runs a method on WKWebView called `evaluateJavaScript:completionHandler:`
> On Android, `injectedJavaScript` runs a method on the Android WebView called `evaluateJavascriptWithFallback`

#### The `injectJavaScript` method

While convenient, the downside to the previously mentioned `injectedJavaScript` prop is that it only runs once. That's why we also expose a method on the webview ref called `injectJavaScript` (note the slightly different name!).

```jsx
import React, { Component } from "react";
import { View } from "react-native";
import { WebView } from "react-native-webview";

export default class App extends Component {
  render() {
    const run = `
      document.body.style.backgroundColor = 'blue';
      true;
    `;

    setTimeout(() => {
      this.webref.injectJavaScript(run);
    }, 3000);

    return (
      <View style={{ flex: 1 }}>
        <WebView
          ref={r => (this.webref = r)}
          source={{
            uri:
              "https://github.com/react-native-community/react-native-webview"
          }}
        />
      </View>
    );
  }
}
```

After 3 seconds, this code turns the background blue:

<img alt="Screenshot of app showing injected javascript" width="200" src="https://user-images.githubusercontent.com/1479215/53670433-93a98280-3c2f-11e9-85a5-0e4650993817.png" />

*Under the hood*

> On iOS, `injectJavaScript` calls WKWebView's `evaluateJS:andThen:`
> On Android, `injectJavaScript` calls Android WebView's `evaluateJavascriptWithFallback` method

#### The `window.ReactNativeWebView.postMessage` method and `onMessage` prop

Being able to send JavaScript to the web page is great, but what about when the web page wants to communicate back to your React Native code? This where `window.ReactNativeWebView.postMessage` and the `onMessage` prop come in.

You _must_ set `onMessage` or the `window.ReactNativeWebView.postMessage` method will not be injected into the web page.

`window.ReactNativeWebView.postMessage` only accepts one argument which must be a string.

```jsx
import React, { Component } from "react";
import { View } from "react-native";
import { WebView } from "react-native-webview";

export default class App extends Component {
  render() {
    const html = `
      <html>
      <head></head>
      <body>
        <script>
          setTimeout(function () {
            window.ReactNativeWebView.postMessage("Hello!")
          }, 2000)
        </script>
      </body>
      </html>
    `;

    return (
      <View style={{ flex: 1 }}>
        <WebView
          source={{ html }}
          onMessage={event => {
            alert(event.nativeEvent.data);
          }}
        />
      </View>
    );
  }
}
```

This code will result in this alert:

<img alt="Alert showing communication from web page to React Native" width="200" src="https://user-images.githubusercontent.com/1479215/53671269-7e822300-3c32-11e9-9937-7ddc34ba8af3.png" />