[英]Lag by taking an instance of an array using es6
我在記錄數組實例時得到了一個空數組!
onSelectMultipleImage = (event): Promise<any> => {
return new Promise(resolve => {
const files = <File[]>event.target.files;
let file: File;
let counter = -1;
const response = [];
while (file = files[++counter]) {
const reader: FileReader = new FileReader();
reader.onload = ((f) => {
return () => {
response.push({
file: f,
base64: reader.result
})
}
})(file);
reader.readAsDataURL(file);
console.log(counter);
if(counter == files.length -1) {
console.log('inside the while');
resolve(response);
}
}
});
};
onImagesSelect = async (event: Event) => {
this.newImages = await this.helper.onSelectMultipleImage(event) || [];
console.log(this.newImages, "Original"); // [file: File, base64: "base 64 long string..."]
console.log([...this.newImages],"instance"); // [] empty array
setTimeout(() => {console.log([...this.newImages, 'instance'])}, 2000); // [file: File, base64: "base 64 long string..."]
}
那么為什么我要得到呈現的結果? 這是由數組內顯示的base64引起的嗎? 如果是,解決方案是什么?
它不等待reader.onload
完成。 因此resolve(response)
在response.push
之前被調用。
您可以創建一個承諾來讀取一個文件並通過Promise.all
將它們返回,就像下面的代碼一樣。
readFile = (file: File): Promise<any> => {
return new Promise(resolve => {
const reader: FileReader = new FileReader();
reader.onload = (f) => {
resolve({
file: f,
base64: reader.result
});
};
reader.readAsDataURL(file);
})
}
onSelectMultipleImage = (event): Promise<any> => {
const files = <File[]>event.target.files;
return Promise.all(files.map(file => readFile(file)));
};
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.