Javascript 使用画布缩放图像并等待结果
我正在使用上传文件Javascript 使用画布缩放图像并等待结果,javascript,reactjs,async-await,html5-canvas,react-dropzone,Javascript,Reactjs,Async Await,Html5 Canvas,React Dropzone,我正在使用上传文件 <Dropzone accept="image/jpeg" multiple onDrop={(acceptedFiles, rejectedFiles) => this.onDrop(acceptedFiles, rejectedFiles)} /> 然后,我构造的requestParams对象将被发送到服务器。我的问题是,我希望客户端代码等待它遍历所有图像并构造最终的requestParams对象。现在不是这样。如何使上述代码等待?可以通过
<Dropzone
accept="image/jpeg"
multiple
onDrop={(acceptedFiles, rejectedFiles) => this.onDrop(acceptedFiles, rejectedFiles)}
/>
然后,我构造的
requestParams
对象将被发送到服务器。我的问题是,我希望客户端代码等待它遍历所有图像并构造最终的requestParams
对象。现在不是这样。如何使上述代码等待?可以通过以下方式实现:
async constructRequestParams(acceptedFiles: Array<Object>) {
return new Promise((resolve) => {
const requestParams = {
parameters: {
generateContourImages: false,
},
images: [],
};
acceptedFiles.forEach(async (acceptedFile, index) => {
const { width, height } = await browserImageSize(acceptedFile);
const imagedata = await this.scaleImage(acceptedFile, width, height);
requestParams.images.push({
imagedata,
methods: methods,
imageID: uuidv4(),
});
if (requestParams.images.length === acceptedFiles.length) {
resolve(requestParams);
}
});
})
}
async onDrop(acceptedFiles: Array<Object>, rejectedFiles: Array<Object>) {
if (acceptedFiles.length) {
const requestParams = await this.constructRequestParams(acceptedFiles);
} else {
this.setState({ error: true });
}
}
异步constructRequestParams(acceptedFiles:Array){
返回新承诺((解决)=>{
常量requestParams={
参数:{
GenerateTourimages:false,
},
图像:[],
};
forEach(异步(acceptedFile,index)=>{
const{width,height}=等待浏览图像大小(acceptedFile);
const imagedata=wait this.scaleImage(acceptedFile,width,height);
requestParams.images.push({
图像数据,
方法:方法,,
imageID:uuidv4(),
});
if(requestParams.images.length==acceptedFiles.length){
解决(请求参数);
}
});
})
}
异步onDrop(acceptedFiles:Array,rejectedFiles:Array){
if(acceptedFiles.length){
const requestParams=wait this.constructRequestParams(acceptedFiles);
}否则{
this.setState({error:true});
}
}
async scaleImage(fileImage: Object, originalWidth: number, originalHeight: number) {
return new Promise((resolve) => {
const imageURL = URL.createObjectURL(fileImage);
const image = new Image();
image.onload = () => {
const scaleFactor = Math.max(originalWidth, originalHeight) / 1000;
const canvas = document.createElement('canvas');
canvas.width = originalWidth;
canvas.height = originalHeight;
const scaledWidth = Math.floor(originalWidth / scaleFactor);
const scaledHeight = Math.floor(originalHeight / scaleFactor);
const ctx = canvas.getContext('2d');
ctx.drawImage(image, 0, 0, scaledWidth, scaledHeight);
const base64 = canvas.toDataURL('image/jpeg');
resolve(base64.substr(23));
}
image.src = imageURL;
});
}
async constructRequestParams(acceptedFiles: Array<Object>) {
return new Promise((resolve) => {
const requestParams = {
parameters: {
generateContourImages: false,
},
images: [],
};
acceptedFiles.forEach(async (acceptedFile, index) => {
const { width, height } = await browserImageSize(acceptedFile);
const imagedata = await this.scaleImage(acceptedFile, width, height);
requestParams.images.push({
imagedata,
methods: methods,
imageID: uuidv4(),
});
if (requestParams.images.length === acceptedFiles.length) {
resolve(requestParams);
}
});
})
}
async onDrop(acceptedFiles: Array<Object>, rejectedFiles: Array<Object>) {
if (acceptedFiles.length) {
const requestParams = await this.constructRequestParams(acceptedFiles);
} else {
this.setState({ error: true });
}
}