1.modal點選其他區域消失

<TouchableWithoutFeedback
    onPress={()=>this.setState({showTopMenu:false})}>
    <View style={{position: 'absolute',left: 0,right: 0,top: 0,bottom: 0,width: null,}}/>
</TouchableWithoutFeedback>

2.圖片做背景

<Image
    style={styles.img}
    source
 
={require('../image/IMG_0026.jpg')}
    resizeMode='cover'
/>

img: {
    position: 'absolute',
    left: 0,
    right: 0,
    top: 0,
    bottom: 0,
    height: null,
    width: null,
},