Angular 文件拖放只允许单个文件

Question

如何只允许拖放文件？使用普通上传按钮，它受到限制，但拖放不起作用。

我唯一已知的解决方法是现在出现一个对话框，向用户显示他选择的所有文件并强制他选择其中一个文件。

Answer 1

通常，您有一个输入类型文件和一个可拖动区域，请参阅 a stackblitz example

<div draggable="true" ngClass="{{dragAreaClass}}">
    <div class="row">
        <div class="col-md-12 text-center">
            Drag files here
            <a href="javascript:void(0)" (click)="file.click()">
                or click to open
            </a>
            <input type="file"
                   #file
                   [multiple]="false"
                   (change)="onFileChange($event)"
                   style="display:none" />
        </div>
        </div>
    </div>
    <div class="error" *ngIf="error">
        Only one file at time allow
    </div>

您在哪里定义了 .css

.error {
    color: #f00;
}

.dragarea {
    font-size: 1.5rem;
    border: 3px solid #bbb;
    padding: 1.5rem;
    background-color: #fff;
    color: #bbb;
}

.droparea {
  font-size: 1.5rem;
  border: 3px dashed #bbb;
  padding: 1.5rem;
  background-color: #eff;
  color: #aaa;
}

并创建一个组件

  error: string;
  dragAreaClass: string;
  onFileChange(event: any) {
    let files: FileList = event.target.files;
    this.saveFiles(files);
  }
  ngOnInit() {
    this.dragAreaClass = "dragarea";
  }
  @HostListener("dragover", ["$event"]) onDragOver(event: any) {
    this.dragAreaClass = "droparea";
    event.preventDefault();
  }
  @HostListener("dragenter", ["$event"]) onDragEnter(event: any) {
    this.dragAreaClass = "droparea";
    event.preventDefault();
  }
  @HostListener("dragend", ["$event"]) onDragEnd(event: any) {
    this.dragAreaClass = "dragarea";
    event.preventDefault();
  }
  @HostListener("dragleave", ["$event"]) onDragLeave(event: any) {
    this.dragAreaClass = "dragarea";
    event.preventDefault();
  }
  @HostListener("drop", ["$event"]) onDrop(event: any) {
    this.dragAreaClass = "dragarea";
    event.preventDefault();
    event.stopPropagation();
    if (event.dataTransfer.files) {
      let files: FileList = event.dataTransfer.files;
      this.saveFiles(files);
    }
  }

  saveFiles(files: FileList) {
    if (files.length > 1) this.error = "Only one file at time allow";
    else {
      this.error = "";
      console.log(files[0].size,files[0].name,files[0].type);

      ..use a sevice to upload file...
    }
  }

看到在函数 saveFiles 中你可以检查 "files" 的长度，其他你可以检查的是扩展名，大小....

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