如何在 React Native 中 return 变量？

Question

我有一个应用程序，我可以根据给定的文本和图片制作一个 pdf 文件。

takePicture 相机组件应用程序中的功能拍照，获取照片的宽度和高度，计算比例并将所有信息保存到 AsyncStorage。它工作正常。

问题是当我试图在不同的组件中获取 AsyncStorage 数据时。

问题是：我怎样才能return这个const height？我想在 pdf 图像绘图中使用它。尝试了不同的方法，但 none 有效。

    getImageHeight = async () => {
        try {
          const height = await AsyncStorage.getItem('asyncimageHeight')
      
          if (height!== null) {
            console.log(`Height from AsyncStorage is: ${height}`)
          }
        } catch (e) {
          alert('Failed to fetch the data from storage')
        }
      }
      getImageHeight();

下面是takePicture如果它能帮助你理解问题的重点：

takePicture = async() => {
    
    if (this.camera) {
        const options = { quality: 0.5, base64: true , fixOrientation: true};
        const data = await this.camera.takePictureAsync(options);
        console.log(data.uri);


        Image.getSize(data.uri, (width, height) => { // Get image width and height of the picture
            let imageWidth = width;
            let imageHeight = height;

            let stringImageWidth = '' + imageWidth; // Makes string for saving in AsyncStorage, allows only strings
            let stringImageHeight = '' + imageHeight;

            const horizontalRatioCalc = () => { // Calculating image ratio for horizontal pictures
                return (imageWidth/imageHeight);
              };
            
            
            const verticalRatioCalc = () => {
                return (imageWidth/imageHeight);
            };

            horizontalImageRatio = horizontalRatioCalc();
            verticalImageRatio = verticalRatioCalc();
        
            stringHorizontalImageRatio = '' + horizontalImageRatio;
            stringVerticalImageRatio = '' + verticalImageRatio;

            console.log(`Size of the picture ${imageWidth}x${imageHeight}`);


            horizontalRatio = async () => {
                if (imageHeight>imageWidth) {

                    verticalRatioCalc();

                    try {
                        AsyncStorage.setItem("imageVerticalRatio", stringVerticalImageRatio), // Save image ratio, height and width to AsyncStorage
                        AsyncStorage.setItem("asyncimageWidth", stringImageWidth),
                        AsyncStorage.setItem("asyncimageHeight", stringImageHeight),
                        
                        console.log(`Vertical ratio saved! It's ${stringVerticalImageRatio}`),
                        console.log(`Image Width saved! It's ${stringImageWidth}`),
                        console.log(`Image height saved! It's ${stringImageHeight}`)
    
                    }   catch (e) {
                        console.log(`AsyncStorage saving of image vertical ratio cannot be done.`)
                    }
                }if (imageHeight<imageWidth) {
                    
                    horizontalRatioCalc();

                    try {
                        AsyncStorage.setItem("imageHorizontalRatio", stringHorizontalImageRatio),
                        AsyncStorage.setItem("asyncimageWidth", stringImageWidth),
                        AsyncStorage.setItem("asyncimageHeight", stringImageHeight),

                        console.log(`Horizontal ratio saved! It's ${stringHorizontalImageRatio}`),
                        console.log(`Image Width saved! It's ${stringImageWidth}`),
                        console.log(`Image height saved! It's ${stringImageHeight}`)
    
                    }   catch (e) {
                        console.log(`AsyncStorage saving of image vertical ratio cannot be done.`)
                    }
                }
            }
            horizontalRatio();


            }, (error) => {
            console.error(`Cannot size of the image: ${error.message}`);
            
        });
        back(data.uri)
    }
};

Answer 1

现在我解决了那个案子，终于太容易了:)

readData = async () => {
        try {
          kuvakorkeus = await AsyncStorage.getItem('asyncimageHeight')
          kuvaleveys = await AsyncStorage.getItem('asyncimageWidth')

          vertikaaliratio = await AsyncStorage.getItem('imageVerticalRatio')
          horisontaaliratio = await AsyncStorage.getItem('imageHorizontalRatio')
      
          if (kuvakorkeus !== null) {
            return kuvakorkeus; // <-- That makes you able to you this variable outside of the function.
          }
        } catch (e) {
          alert('Failed to fetch the data from storage')
        }
      }
      readData ();

如何在 React Native 中 return 变量？

How to return variable in React Native?

react-native

asyncstorage