這是Contoso大學在線示例代碼:ViewBag
控制器:
[HttpGet]
public ActionResult Edit(int id)
{
Department department = departmentService.GetById(id);
PopulateAdministratorDropDownList(department.PersonID);
return View(department);
}
// POST: /Department/Edit/5
[HttpPost]
public ActionResult Edit(Department department)
{
try
{
if (ModelState.IsValid)
{
departmentService.Update(department);
return RedirectToAction("Index");
}
}
catch (DataException)
{
//Log the error (add a variable name after DataException)
ModelState.AddModelError("", "Unable to save changes. Try again, and if the problem
persists, see your system administrator.");
}
PopulateAdministratorDropDownList(department.PersonID);
return View(department);
}
private void PopulateAdministratorDropDownList(object selectedAdministrator = null)
{
var administrators = instructorService.GetAll().OrderBy(i => i.LastName);
ViewBag.PersonID = new SelectList(administrators, "PersonID", "FullName",
selectedAdministrator);
}
查看:
<div class="editor-field">
@Html.DropDownList("PersonID", String.Empty)
@Html.ValidationMessageFor(model => model.PersonID)
</div>
我的問題是:如果在查看我們不訪問ViewBag.PersonID(我們只是創建一個DropDownList,它生成ID =「PersonID」的html選擇列表,沒有任何默認的選定值),ViewBag.PersonID屬性如何綁定到DropDownList?幕後發生了什麼?這看起來像魔術!
第二個問題是發佈數據時,我認爲控制器在視圖中搜索任何與表單中的模型屬性相匹配的html表單字段,這就是我們如何在回發中獲取選定的Department.PersonID,即使視圖代碼不會引用模型(像model => model.PersonID),對嗎?