Angular2 下拉菜单恢复为之前选择的选项

Question

我有这个简单的 HTML 选择来在 Angular2 (TS) 中实现下拉菜单，如下所示

<select id="pageSize" (change)="onPageSizeChanged($event, pagination.pageSize)">
  <option value="10">10</option>
  <option value="20">20</option>
  <option value="50">50</option>
</select>

先前选择的值保持pagination.pageSize可变。在改变这一点时，我想打开一个对话框并等待用户响应。如果用户单击取消，我想将选择恢复为以前选择的选项。

onPageSizeChanged(event, oldValue) {
  const response = window.confirm("Are you sure you want change the page size? Your edits will be lost?");
  if (response) {
    //... some code ...
  } else {
    //... here I want to revert the selection to previously selected option
  }
}

尝试了很多不同的事情，但没有运气。

请帮忙，我对这个简单的事情失去了理智。我一定是在做蠢事。

---

尝试 #1 - 没有用（Plunk - https://embed.plnkr.co/ILi12O/）

<select id="pageSize" [ngModel]="pageSize" (ngModelChange)="onPageSizeChanged($event, pagination.pageSize)"> 
  <option value="10">10</option> 
  <option value="20">20</option> 
  <option value="50">50</option> 
</select> 

onPageSizeChanged(event, oldValue) { 
  const response = window.confirm("Are you sure you want change the page size? Your edits will be lost?"); 
  if (response) { //go ahead so something } 
  else { this.pageSize = oldValue; }  
} 

Answer 1

添加ngModelChange以跟踪模型更改。如果对话框确认下一次更改，则保留更改，否则设置回该值。本地模板变量 (#select) 更容易跟踪。我根据你的笨蛋做了修改：

HTML：

 <select #select id="pageSize" [ngModel]="pageSize" (ngModelChange)="select.value = onPageSizeChanged($event)"> 

打字稿：

   onPageSizeChanged(event) { 
   const response = window.confirm("Are you sure you want change the page size? Your edits will be lost?"); 
    console.log(this.pagination.pageSize)
    if (response) { 
      this.pageSize = event;
      this.pagination.pageSize = event;
    }
    else{
      this.pageSize = this.pagination.pageSize;
    }
    return this.pagination.pageSize;
  } 

演示