将文件从FileReader传递到Angular 6中的表单输入

Question

我尝试创建一个UI,其中有一个带有几个文本字段的表单,a input type="file"和a div可以删除要与表单其余部分一起上传的图像.

我的目标/逻辑

使用相同的方法div来删除图像或单击它并打开文件夹资源管理器,如input type="file"行为.在小屏幕中启用点击是有意义的,实际上不可能"拖放".并且由于input type="file"表格中已经有一个没有理由从中获取图像div并将其附加到表格等等.我尝试拍摄掉的图像div,将其设置为值input type="file"并提交形成一次.(如果用户点击了div,那么input type="file"已经有了一个值,所以我可以再次自由提交表单).

这是代码

  <div id="imageDrop" (click)='imageInput.click()' (drop)="drop($event)" (dragover)="allowDrop($event)" #imageDrop>
  </div> 
  <input type="file" formControlName="imageInput" required #imageInput id="imageInput" (change)='imageChange($event)' > <!-- use css to hide it -->

所以,当imageDrop点击时,实际上调用imageChangevia(click)='imageInput.click()'

这是组件中的打字稿.

//imageUpload is the name of the reactive form
acceptedImageTypes = {'image/png': true,'image/jpeg': true,'image/gif': true};
@ViewChild('imageDrop') imageDrop; 

allowDrop(e) {
    e.preventDefault();
  }

  drop(e) {
    e.preventDefault();  
     //clear in case we selected something before via click
    this.imageUpload.controls.imageInput.reset();  
    this.imageDrop.innerHTML="";    
    this.checkfiles(e.dataTransfer.files);
  }

  imageChange(event){    
    this.imageDrop.innerHTML="";   
    this.checkfiles(event.target.files);    
  }//imageChange

  checkfiles(files){      
    if (this.acceptedImageTypes[files[0].type] !== true){
      this.imageDrop.nativeElement.innerHTML="Not an image";          
      return;   
    }
    else if (files.length>1){
      this.imageDrop.nativeElement.innerHTML="Only one image/time";           
      return;   
    }    
    else { this.readfiles(files); }
  }//checkfiles

  readfiles(files){
    const reader = new FileReader();
    let image = new Image();
    reader.onload =  (event) =>{
      this.imageDrop.nativeElement.innerHTML="";                
      let fileReader = event.target as FileReader;
      image.src = fileReader.result;
      image.width = 150; 
      this.imageDrop.nativeElement.appendChild(image);      
    };
    reader.readAsDataURL(files[0]);    

    if (this.imageUpload.controls.imageInput.value==null) {
        //if its null then means that we dragging an img, so the previous image from the input file is deleted
        //now we got to put this image to the input file in order to submit the form
      this.imageUpload.controls.imageInput.reset(files[0] );            
    }    
  }//readfiles

  imageUploadSubmitted(){
    //when form submit, for now just check image value to check if its the right one
    console.log('IMAGE VALUE SUBMIT = =  ',this.imageUpload.controls.imageInput.value);
  }

错误

当我尝试拖放图像时,我得到的ERROR DOMException: Failed to set the 'value' property on 'HTMLInputElement': This input element accepts a filename, which may only be programmatically set to the empty string指向此HTML行,<div id="imageDrop" (click)='imageInput.click()' (drop)="drop($event)" (dragover)="allowDrop($event)" #imageDrop>但我确信它与

if (this.imageUpload.controls.imageInput.value==null) {
  this.imageUpload.controls.imageInput.reset(files[0] );            
} 

部分readfiles功能.

任何想法如何解决这个问题,所以文件输入可以得到一个值,然后可以自由提交表单？

谢谢

Answer 1

好吧,给你错误的那条线是 this.imageUpload.controls.imageInput.setValue(files[0]);

原因是,浏览器将阻止您因安全问题以编程方式设置文件.

相反,您可以e.dataTransfer.files直接使用:

let input = this.imageUpload.controls.imageInput as any;
input.files = files;  

这是你的stackblitz的一个分支