如何更新变量react native

Question

我有一个应用程序，我需要知道图片的比例，以便稍后调整大小。用户可以水平和垂直拍照。当然，比例也会发生变化。所以我需要得到两个不同的比率。

更新let horizontalImageRatio = 0;时出现问题

我该怎么解决这个问题，有什么建议吗？

我的代码：

Image.getSize(data.uri, (width, height) => { // Pickuping size of the picture

let imageWidth = width;
let imageHeight = height;
let stringImageWidth = '' + imageWidth; // Make double to string for storing to asyncstorage
let stringImageHeight = '' + imageHeight;

let horizontalImageRatio = 0; // this value should be updated
let verticalImageRatio = 0;

// For updating let horizontalImageRatio, but not working outside of this <-- PROBLEM
const horizontalRatioCalc = () => {
horizontalImageRatio = imageWidth/imageHeight;
console.log('horizontal_update', horizontalImageRatio);
};

const verticalRatioCalc = () => {
verticalImageRatio = imageWidth/imageHeight;
console.log('vertical_update', verticalImageRatio);
};

let stringHorizontalImageRatio = '' + horizontalImageRatio;
let stringVerticalImageRatio = '' + verticalImageRatio;
console.log(`Size of the picture ${imageWidth}x${imageHeight}`); // Tells size of the image for the console

horizontalRatio = async () => {
if (imageHeight>imageWidth) {
verticalRatioCalc();
try {
AsyncStorage.setItem("imageVerticalRatio", stringVerticalImageRatio),
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.`)
}
}else {

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();

Answer 1

因此，显然，您无法访问horizontalRatioCalc内部的horizontalImageRatio，方法horizontalRatioCalc具有不同的作用域。您可以更改horizontalRatioCalc以接收参数并返回值，就像我在本例中所做的那样：https://stackblitz.com/edit/react-xiysai这很好，因为现在你有了一个可以独立测试的功能。

或者你也可以这样做：https://stackblitz.com/edit/react-variable-scope通过这种方式，您可以同时访问变量和方法。