javascript - 用dialog.showSaveDialog实现 promise 拒绝

Question

我正在尝试通过以下两种方法来实现dialog.showSaveDialog的文件保存:
方法1:

const pObj = dialog.showSaveDialog(window, options);
pObj.then(
  onResolved => {
    filename = onResolved.filePath;
    fs.writeFileSync(filename, arg);
  },
  onRejected => {console.log('Promise rejected')}
);

方法2:

const pObj = dialog.showSaveDialog(window, options);
pObj.then(
  onResolved => {
    filename = onResolved.filePath;
    fs.writeFileSync(filename, arg);
  }
).catch(err => {
  console.log('No file saved');
});

当我在对话框窗口中单击 Cancel而不是 Save时，方法1向我抛出一条错误消息，提示未捕获到Promise错误。方法2运作良好(即显示文字 No file saved。
为什么方法1中的 pObj不执行 onRejected处理程序？ then()方法不接受两个处理程序，一个用于解决状态，一个用于拒绝状态吗？感谢您的解释。

Answer 1

then()方法确实确实接受两个处理程序，一个用于解决状态，一个用于拒绝状态。仅当出现问题时才调用reject处理程序；但是，单击Cancel而不是Save 不会触发错误，它只是通过resolve处理程序返回了不同的结果。
有关dialog.showSaveDialog()的文档中对此进行了明确说明:

Returns Promise<Object> - Resolve with an object containing thefollowing:

• canceled Boolean - whether or not the dialog was canceled.

• filePath String (optional) - If the dialog is canceled, this will be undefined.

然后，这应该起作用(未经测试):

const pObj = dialog.showSaveDialog(window, options);
pObj.then(
  onResolved => {
    if (!onResolved.canceled) {
        filename = onResolved.filePath;
        fs.writeFileSync(filename, arg);
    }
  },
  onRejected => {console.log('Promise rejected')}
);