我正在尝试在验证后将一些图像信息发送到模板。但是我没有。
转到模板的变量在回调中,或者在异步函数中,并且我不知道将此信息发送到模板。
能帮我解决这个问题吗?我已经尝试了一切。
event.component.ts
import "rxjs/Rx";
import {Component} from '@angular/core';
@Component({
selector: '<my-image></my-image>',
templateUrl: './event.component.html',
})
export class EventComponent {
files: File[];
file: any
imageName: any;
imageSize: any;
whithImage = false;
ngOnInit() {this.files = []}
onFileSelect(event) {
this.files = event.dataTransfer ? event.dataTransfer.files : event.target.files;
this.file = this.files[0];
this.isImage(this.file, function(res, file){
if(res==true){
this.imageName = file.name;
this.imageSize = file.size;
this.whithImage = res;
}
})
}
isImage(file, callback) {
var reader = new FileReader();
reader.onload = function(event) {
var contents = reader.result;
var buf = new Uint8Array(contents);
if(buf[0] === 0xFF && buf[1] === 0xD8 && buf[2] === 0xFF){
callback(true, file) //jpg
}else{callback(false)}
};
reader.readAsArrayBuffer(file);
}
onChooseClick(event, fileInput) {
fileInput.value = null;
}
event.component.html
<span (click)="onChooseClick($event, fileinput)">
Image<input #fileinput type="file" (change)="onFileSelect($event)"/>
</button>
<div *ngIf="whithImage">
<p>{{ imageName }}</p>
<p>{{ imageSize }}</p>
</div>
最佳答案
尝试@peeskillet首先建议的内容-即通过使用arrow function使用正确的this
上下文:
export class EventComponent {
onFileSelect(event) {
...
this.isImage(this.file, (res, file) => { // <----
if(res==true) {
this.imageName = file.name;
this.imageSize = file.size;
this.whithImage = res;
}
});
}
如果这不起作用,则Angular不会知道如何猴子化您的异步事件,因此,当事件触发时,Angular更改检测将不会运行(因此您的视图不会更新以反映新的组件属性值) 。您需要manually trigger change detection。这是一种实现方法:
import {ChangeDetectorRef} from '@angular/core'; // <-----
export class EventComponent {
constructor(private cdref:ChangeDetectorRef) {} // <-----
onFileSelect(event) {
...
this.isImage(this.file, (res, file) => { // <----
if(res==true) {
this.imageName = file.name;
this.imageSize = file.size;
this.whithImage = res;
this.cdref.detectChanges(); // <------
}
});
}