Assigning a file to a Variable using angular forms and ngModel

问题

I want to use a form to assign a file to a variable so that I can then post the file to my back end server.

My form looks like the following:

<form (ngSubmit)='onSubmit()' #myform='ngform'>
<div class="fileup">
    <label for='file'> Upload </label>
    <input id='file' type='file' name='file' [(ngModel)] = 'uploadedFile' />
    <button type='submit' class='btn btn-basic'> Upload </button>
</form>


{{ uploadedFile ¦ json }}

The final line is just for development purposes and allows me to see the value of the 'uploadedFile' variable.

My in my TS file i have defined the variable simply as:

uploadedFile: any

For any type of input other than file this method works, in that, the Variable updates to show what has been entered. However for the file when I browse and select a file, the variable remains empty. I confirm this by outputting the variable 'uploadedFile' to the console when i click submit. But the variable is returned as 'undefined' even after I have selected a file. What has to be done to assign the file to this uploadedFile variable?

回答1:

You should do this:

html:

<form (ngSubmit)='onSubmit()' #myform='ngform'>
<div class="fileup">
    <label for='file'> Upload </label>
    <input id='file' type="file" (change)="onFileChange($event)" />
    <button type='submit' [disabled]="formGroup.invalid || formGroup.prestine" class='btn btn-basic'> Upload </button>
</form>


{{ uploadedFile ¦ json }}

THen in your Component.ts

export class CustomComponent {

  formGroup = this.fb.group({
    file: [null, Validators.required]
  });

  constructor(private fb: FormBuilder, private cd: ChangeDetectorRef) {}

  onFileChange(event) {
    const reader = new FileReader();

    if(event.target.files && event.target.files.length) {
      const [file] = event.target.files;
      reader.readAsDataURL(file);

      reader.onload = () => {
        this.formGroup.patchValue({
          file: reader.result
       });

        // need to run CD since file load runs outside of zone
        this.cd.markForCheck();
      };
    }
  } 
}

In Conclusion: every time you upload a new file you will update the FormGroup.

Here you have another example: https://medium.com/@amcdnl/file-uploads-with-angular-reactive-forms-960fd0b34cb5

来源：https://stackoverflow.com/questions/59269915/assigning-a-file-to-a-variable-using-angular-forms-and-ngmodel

标签

angular

forms

file

upload

angular-forms