ModelState.isValid - false

Question

我想從html頁面上的dropdownList中獲取參數並將其發送到我的控制器，創建新的Model對象並將其插入到數據庫中。

這是我的控制器（兩種方法來創建My_Model）：

public ActionResult Create() 
    { 
     IEnumerable<MusicStyle> musicStyleList = db.MusicStyles.ToList(); 
     ViewData["musicStyles"] = new SelectList(musicStyleList); 
     return View(); 
    } 

    // POST: Bands/Create 
    // To protect from overposting attacks, please enable the specific properties you want to bind to, for 
    // more details see http://go.microsoft.com/fwlink/?LinkId=317598. 
    [HttpPost] 
    [ValidateAntiForgeryToken] 
    public ActionResult Create([Bind(Include = "id,name,info,appearanceDate,musicStyles")] Band band) 
    { 
     IEnumerable<MusicStyle> musicStyleList; 
     if (ModelState.IsValid) 
     { 
      musicStyleList = db.MusicStyles; 
      ViewData["musicStyles"] = new SelectList(musicStyleList).ToList(); 
      db.Bands.Add(band); 
      db.SaveChanges(); 
      return RedirectToAction("Index"); 
     } 
     musicStyleList = db.MusicStyles; 
     ViewData["musicStyles"] = new SelectList(musicStyleList).ToList(); 
     return View(band); 
    } 

這是我的html頁面上下拉列表：

@Html.DropDownList("musicStyles", "select style") 

這是我的模型：

public class Band 
{ 
    [Required] 
    public int id { get; set; } 

    [Required] 
    [RegularExpression(@"^[a-zA-Z-\s\\\/*_]+$")] 
    [StringLength(60, MinimumLength = 1)] 
    public string name { get; set; } 

    public string info { get; set; } 

    [Required] 
    [Display(Name = "Appearance date")] 
    [DataType(DataType.Date)] 
    [DisplayFormat(DataFormatString = "{0:dd/MM/yyyy}")] 
    public DateTime appearanceDate { get; set; } 

    public List<MusicStyle> musicStyles { get; set; } 
    public List<Song> songs { get; set; } 
    public List<Album> albums { get; set; } 
} 

它有一個列表musicStyles（引用多對多），我想將選定的元素從dropdownList設置爲此模型。但在Create方法的結果，我有一個null musicStyles，並且ModelState.isValid == false

Answer 1

一個<select>只回發一個價值 - 它不能綁定到財產List<MusicStyle> musicStyles您需要使用性能視圖模型可以綁定到

public class BandVM 
{ 
    [Display(Name = "Music style")] 
    [Required(ErrorMessage = "Please select a style")] 
    public string SelectedMusicStyle { get; set; } 
    public SelectList MusicStyleList { get; set; } 
    .... 
} 

並且在控制器

public ActionResult Create() 
{ 
    BandVM model = new BandVM(); 
    model.MusicStyleList = new SelectList(db.MusicStyles); 
    return View(model); 
} 

，並在視圖

@Html.LabelFor(m => m.SelectedMusicStyle) 
@Html.DropDownListFor(m => m.SelectedMusicStyle, Model.MusicStyleList, "select style") 
@Html.ValidationMessageFor(m => m.SelectedMusicStyle) 

在POST方法

[HttpPost] 
[ValidateAntiForgeryToken] 
public ActionResult Create(BandVM model) // NO Bind.Include! 
{ 
    // model.SelectedMusicStyle will contain the selected value 
    // Create a new instance of the data model and map the view model properties to it 
    // Save and redirect 
}