Javascript React native camera-TypeError:未定义的不是对象

我正在尝试使用“react native camera”为rect本机应用程序使用摄像头。 当我试图导航到摄像头屏幕时，我不断遇到以下错误

这是我的密码：

import React,{Component} from 'react';
import {SafeAreaView,StyleSheet,TouchableOpacity,TextInput,View,Text,StatusBar,Image} from 'react-native';
import {createAppContainer} from 'react-navigation';
import {createStackNavigator} from 'react-navigation-stack';
import UserMainScreen from './UserMainScreen.js';
import Camera from 'react-native-camera';
import {RNCamera} from 'react-native-camera';

class CameraScreen extends Component{
    render(){
        return(
            <View style={cam_styles.container}>
                <Camera ref={cam=>{this.camera = cam;}} style={cam_styles.preview} aspect = {Camera.constants.Aspect.fill}>
                        <Text style={cam_styles.capture} onPress={this.takePicture.bind(this)}>[CAPTURE]</Text>
                    </Camera>
            </View>
        );
    }

    takePicture(){
        const options ={};
        this.camera.capture({metadata: options})
        .then(data=>console.log(data))
        .catch(error=>console.log(error));
    }
}

const cam_styles = StyleSheet.create({
    container: {
        flex:1,
        flexDirection: 'row',
    },
    preview:{
        flex:1,
        justifyContent: 'flex-end',
        alignItems:'center'
    },
    capture:{
        flex:0,
        backgroundColor: '#fff',
        borderRadius: 5,
        color:'#000',
        padding:10,
        margin:40
    }
});

const MainNavigator = createStackNavigator({
    Home: UserMainScreen,
    Login : LoginScreen,
    Camera : CameraScreen,
},
    {
        initialRouteName: 'Login',
        headerMode: 'none',
    }
);
const AppContainer = createAppContainer(MainNavigator);

class Login extends Component{

    render (){      
        return (
                <AppContainer />   
        );
    }
}
export default Login;

---

如果您正在使用expo，请从“react native camera”中注释出您的

导入{RNCamera}并使用
从“expo”导入{Camera}如果您没有使用expo，则执行相反的操作

将世博会呈现为：

从“expo”导入{Camera}；
类CameraScreen扩展组件{
render（）{
返回(
{this.camera=cam；}}style={cam_styles.preview}aspect={camera.constants.aspect.fill}>
[捕获]
);
}

以非expo方式呈现：

从'react native camera'导入{RNCamera}；
类CameraScreen扩展组件{
render（）{
返回(
{this.camera=cam；}}style={cam_styles.preview}aspect={camera.constants.aspect.fill}>
[捕获]
);
}

TypeError: undefined is not an object (evaluating '_reactNativeCamera.Camera.constants')

This error is located at:
    in CameraScreen (at SceneView.js:9)
    in SceneView (at StackViewLayout.tsx:900)
    in RCTView (at createAnimatedComponent.js:151)
    in AnimatedComponent (at StackViewCard.tsx:106)
    in RCTView (at createAnimatedComponent.js:151)
    in AnimatedComponent (at screens.native.js:71)
    in Screen (at StackViewCard.tsx:93)
    in Card (at createPointerEventsContainer.tsx:95)
    in Container (at StackViewLayout.tsx:975)
    in RCTView (at screens.native.js:101)
    in ScreenContainer (at StackViewLayout.tsx:384)
    in RCTView (at createAnimatedComponent.js:151)
    in AnimatedComponent (at StackViewLayout.tsx:374)
    in PanGestureHandler (at StackViewLayout.tsx:367)
    in StackViewLayout (at withOrientation.js:30)
    in withOrientation (at StackView.tsx:104)
    in RCTView (at Transitioner.tsx:267)
    in Transitioner (at StackView.tsx:41)
    in StackView (at createNavigator.js:80)
    in Navigator (at createKeyboardAwareNavigator.js:12)
    in KeyboardAwareNavigator (at createAppContainer.js:430)
    in NavigationContainer (at Login.js:97)
    in Login
    in RCTView (at AppContainer.js:101)
    in RCTView (at AppContainer.js:119)
    in AppContainer (at renderApplication.js:39)

CameraScreen#render
    Login.js:42:100
renderRoot
    [native code]:0
runRootCallback
    [native code]:0
unstable_runWithPriority
    scheduler.development.js:643:23
callFunctionReturnFlushedQueue
    [native code]:0