javascript – ngFor在Angular 2中从promise中填充的对象

我正在使用filesFromZip对象中的blobURL解析带有图像的zip文件,并使用ngFor迭代它以在页面上显示图像.

看起来像这样

filesFromZip = {};
let zip = new JSZip();

zip.loadAsync(zipfileFromInput)
  .then(function (zip) {
    for (let file in zip.files) {

    let fileInZip = zip.files[file];

    zip.file(fileInZip.name)
      .async("arraybuffer")
      .then(function (content) {
        let buffer = new Uint8Array(content);
        let blob = new Blob([buffer.buffer]);

        // here is where I want to push this object into the filesFromZip object somehow....
        return {
          fileName: fileInZip.name,
          blobURL: URL.createObjectURL(blob)
        };
    });
   }
  });

在模板中：

<md-card *ngFor="let file of filesFromZip">
  <h3 md-line>{{file.fileName}}</h3>
  <img src="{{file.blobURL}}">
</md-card>

如何从promiseFromZip获取数据？

我试图将它推入filesFromZip,但这给了我这个错误：

error_handler.js:47 EXCEPTION: Uncaught (in promise): TypeError:
Cannot read property ‘async’ of null

我真的在与异步和Angular 2争吵.有人可以把我送到正确的方向吗？

解决方法:

首先,您不能使用* ngFor指令迭代普通对象,因此filesFromZip应该是一个数组.

this.filesFromZip = [];
zip.loadAsync(zipfileFromInput)
  .then((zip)=> {
    for (let file in zip.files) {
      let fileInZip = zip.files[file];
      zip.file(fileInZip.name)
        .async("arraybuffer")
        .then((content)=> {
          let buffer = new Uint8Array(content);
          let blob = new Blob([buffer.buffer]);
          // here is where I want to push this object into the filesFromZip object somehow....
          this.filesFromZip.push({
            fileName: fileInZip.name,
            blobURL: URL.createObjectURL(blob)
          });
      });
   }
  });

或者你可以使用Promise.all(),它将从可迭代的Promise中创建一个promise,然后使用异步管道：

javascript：

this.filesFromZip = Promise.all(
  zip.loadAsync(zipfileFromInput)
    .then((zip)=> {
      let out=[];
      for (let file in zip.files) {
        let fileInZip = zip.files[file];
        out.push(zip.file(fileInZip.name)
          .async("arraybuffer")
          .then((content)=> {
            let buffer = new Uint8Array(content);
            let blob = new Blob([buffer.buffer]);
            // here is where I want to push this object into the filesFromZip object somehow....
            this.filesFromZip.push({
              fileName: fileInZip.name,
              blobURL: URL.createObjectURL(blob)
            });
        }));
    }
    return out;
    });
)

模板：

<md-card *ngFor="let file of filesFromZip|async">
  <h3 md-line>{{file.fileName}}</h3>
  <img src="{{file.blobURL}}">
</md-card>

但是,这里的主要问题似乎是zip.file(fileInZip.name)返回null

标签：javascript,blob,angular,jszip
来源： https://codeday.me/bug/20190711/1429511.html