将图像从FileReader传递到Angular 6中的表单输入 [英] Pass image from FileReader to form input in Angular 6

问题描述

我尝试创建一个UI，其中有一个包含几个文本字段的表单，一个input type="file"和div，您可以拖放图像以与表单的其余部分一起上载.

I try to create an UI where there is a form with a couple of text fields, a input type="file" and a div that you can drop images to upload with the rest of the form.

我的目标/逻辑

使用相同的div放下图像或单击它，然后像input type="file"一样打开文件夹资源管理器.在实际上不可能拖放"的小屏幕上，启用单击是有意义的.并且由于表单中已经存在input type="file"，因此没有理由从div中获取图像并将其附加到表单等中.我尝试获取放置在div中的图像，设置将其作为input type="file"中的值，然后提交一次表单. (如果用户单击div，则input type="file"已经具有一个值，因此我可以再次自由提交表单.)

use the same div to either drop an image or click on it and open the folder explorer like the input type="file" behaves. Enabling clicking makes sense in small screens where it is practically impossible to "drag and drop". And since there is already a input type="file" in the form there is no reason to take the image from the div and append it to the form etc etc. I try to take the image that is dropped in the div, set it as a value in the input type="file" and submit the form once. (if user clicked on the div , then the input type="file" already has a value , so again I am free to submit the form again).

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 -->

因此，当单击imageDrop时，实际上是通过(click)='imageInput.click()'

So, when imageDrop is clicked, actually call the imageChange via (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，我得到了指向该HTML行<div id="imageDrop" (click)='imageInput.click()' (drop)="drop($event)" (dragover)="allowDrop($event)" #imageDrop>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，但是我确定它与

When I try to drag/drop an image, I get this 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 that points to this HTML line <div id="imageDrop" (click)='imageInput.click()' (drop)="drop($event)" (dragover)="allowDrop($event)" #imageDrop> but I am sure it is related to the

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

readfiles功能的一部分.

有什么想法可以解决此问题，以便文件输入可以获取值，然后可以自由提交表单吗?

Any ideas how to fix this, so the file input can get a value and be then free to submit the form?

谢谢

推荐答案

好的，给你他错误的行是this.imageUpload.controls.imageInput.setValue(files[0]);

Okay, the line giving you he error was this.imageUpload.controls.imageInput.setValue(files[0]);

原因是，由于安全问题，浏览器将阻止您以编程方式设置文件.

The reason is, the browser will prevent you from programmatically setting the file that way due to security problems.

相反，您可以直接使用e.dataTransfer.files:

Instead, you can use the e.dataTransfer.files directly:

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

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