Expo Camera 仅使用 React Navigation 打开一次

Question

我将 Expo 相机设置为在带有反应导航的中间选项卡上打开。但是，仅当我第一次单击该选项卡时，相机才会打开。如果我关闭它并返回它只是一个黑屏。拍照按钮也没有。 （作为一个整体，我是 React Native 和有点编码的新手）

'use strict';
import React, { Component } from 'react';
import { createBottomTabNavigator } from 'react-navigation';
import { Camera, Permissions } from 'expo';
import {
    AppRegistry,
    Dimensions,
    StyleSheet,
    Text,
    TouchableOpacity,
    View,
    Button
} from 'react-native';


class HomeScreen extends React.Component {
  render() {
    return (
      <View style={{ flex: 1, justifyContent: 'center', alignItems: 'center' }}>
        <Text>Home!</Text>
      </View>
    );
  }
}

class CameraView extends React.Component {
  state = {
    hasCameraPermission: null,
    type: Camera.Constants.Type.back,
  };

  async componentWillMount() {
    const { status } = await Permissions.askAsync(Permissions.CAMERA);
    this.setState({ hasCameraPermission: status === 'granted' });
  }
  render() {
     const { hasCameraPermission } = this.state;
    if (hasCameraPermission === null) {
      return <View />;
    } else if (hasCameraPermission === false) {
      return <Text>No access to camera</Text>;
    } else {
      return (
        <View style={{ flex: 1 }}>
          <Camera style={{ flex: 1 }} type={this.state.type}>
            <View
              style={{
                flex: 1,
                backgroundColor: 'transparent',
                flexDirection: 'row',
              }}>
              <TouchableOpacity
                style={{
                  flex: 0.1,
                  alignSelf: 'flex-end',
                  alignItems: 'center',
                }}
                onPress={() => {
                  this.setState({
                    type: this.state.type === Camera.Constants.Type.back
                      ? Camera.Constants.Type.front
                      : Camera.Constants.Type.back,
                  });
                }}>
                <Text
                  style={{ fontSize: 18, marginBottom: 10, color: 'white' }}>
                  {' '}Flip{' '}
                </Text>
              </TouchableOpacity>
            </View>
          </Camera>
        </View>
      );
    }
  }
}

class SettingsScreen extends React.Component {
  render() {
    return (
      <View style={{ flex: 1, justifyContent: 'center', alignItems: 'center' }}>
        <Text>Settings!</Text>
      </View>
    );
  }
}


export default createBottomTabNavigator({
  Home: HomeScreen,
  Camera:CameraView,
  Settings: SettingsScreen
});

const styles = StyleSheet.create({
    container: {
        flex: 1,
        flexDirection: 'column',
        top: 250
    },

    capture: {
        flex: 0,
        backgroundColor: '#fff',
        borderRadius: 5,
        padding: 15,
        paddingHorizontal: 20,
        alignSelf: 'center',
        margin: 20
    }

});

Answer 1

使用反应导航 5.x

import { useIsFocused } from '@react-navigation/native';

export const CameraView = (props) => {
    const isFocused = useIsFocused();
    return (
       <View>
         { isFocused && <RNCamera  />  }
       </View>
     )
}

useIsFocused Documentation

Answer 2

我遇到了一些问题。

这段代码为我解决了这个问题：

import { withNavigationFocus } from 'react-navigation'

render() {
    const { isFocused } = this.props
    return (
       <View>
         { isFocused && <RNCamera  ... />  }
       </View
     )
}


export default withNavigationFocus(Camera)

Answer 3

要完成这项工作，您需要：

1.

import { NavigationEvents } from 'react-navigation';

state = { loaded: true }

render() {
    const { loaded } = this.state;
        return (
            <View style={styles.container}>
            <NavigationEvents
             onWillFocus={payload => this.setState({loaded: true})}
             onDidBlur={payload => this.setState({loaded: false})}/>
            <View style={styles.cameraArea}>
            {loaded && (
                <Camera
                 type={Camera.Constants.Type.back}
                 ref={ref => {
                     this.camera = ref;
                }}
              />
              )}          
            </View>

这个想法是隐藏这个相机视图（onDidBlur->加载：false），然后当你回来时（onWillFocus被触发并将加载更改为true）。当调用 render() 函数时，它将再次显示<Camera />。 如果您有任何问题，请随时提出。

Answer 4

我通过使用 NavigationEvents 来确定选项卡是否处于焦点位置，然后从那里安装和卸载相机。如果您需要在另一个屏幕上使用它，这也可以释放相机。这是我在你的例子中要做的：

    import { NavigationEvents } from 'react-navigation';
    ...
    class CameraView extends React.Component {
      constructor(props) {
       super(props) 
       this.state = {
         hasCameraPermission: null,
         type: Camera.Constants.Type.back,
         isFocused:true
       };
      }

      ...

      render(){
       //...your existing if's
       } if(this.state.isFocused === false){
         return (
              <NavigationEvents
                    onWillFocus={payload => {
                        //console.log("will focus", payload);
                        this.setState({isFocused:true})
                    }}
                    onDidBlur={payload => {
                        //console.log('did leave',payload)
                        this.setState({isFocused:false})
                    }}
                />
         )
       }
       } else {
          return (
           <View style={{ flex: 1 }}>
            <Camera style={{ flex: 1 }} type={this.state.type}>
               <NavigationEvents
                    onWillFocus={payload => {
                        //console.log("will focus", payload);
                        this.setState({isFocused:true})
                    }}
                    onDidBlur={payload => {
                        //console.log('did leave',payload)
                        this.setState({isFocused:false})
                    }}
                />
          //...the rest of your camera code
      }

我希望它也适合你

Answer 5

我使用来自react-navigation/native 的钩子useIsFocused 解决了它。我在 Android、iOS 和 Web 上对其进行了测试

import { useIsFocused } from '@react-navigation/native';

...

const isFocused = useIsFocused();

...

return (
    isFocused && (
      <Camera
        ref={(ref) => {
          camera = ref;
        }}
        onBarCodeScanned={scanned ? undefined : handleBarCodeScanned}
        style={StyleSheet.absoluteFillObject}
      />
    )
  );

Answer 6

这对我有用。 （导航 5.x） 如果您为 CAMERA 使用不同的屏幕，您可以在移动到另一个屏幕时轻松卸下屏幕。

此行为的原因：任何时候都只能激活一个相机预览 给定的时间。如果你的应用中有多个屏幕，你应该 每当屏幕失焦时卸载相机组件。

<Stack.Screen name="camera" component={CameraScreen} options={{unmountOnBlur: true}}/>
</Stack.Navigator>

文档链接：https://docs.expo.io/versions/latest/sdk/camera/

谢谢。

Answer 7

如果您将 RN Expo 与 React Navigation - Tab Navigator 结合使用。

然后只需使用unmountOnBlur - unmountOnBlur Documentation

这将强制相机在每次导航焦点更改时卸载。