Question

我有一个包含三个元素的ASP.NET页面，每个元素都在一个面板中：
Model #，Manufacturer和Description Model #＆amp; Description是文本字段。 Manufacturer从数据库中获取其值，并通过下拉列表显示它们用户输入Model #，选择Manufacturer，然后输入Description，通过按钮保存记录，并将新模型添加到数据中。

问题是，无论从列表中选择Manufacturer，记录只会与出现的第一个制造商一起保存（因此，如果我选择ZZZManufacturer，它将保存Model #和Description但是使用AAAManufacturer - ddl按字母顺序排序。

我花了最后几个小时的时间在SO＆amp;其他地方似乎是答案，或者至少看起来高度相关 - 元素必须在AutoPostBack，ViewState和后面的代码中的！IsPostBack检查之间正确。

或许是什么使得这个与众不同的是，有一个数据访问层组件 - 可能有什么影响这个？我刚刚继承了这个项目，我还在学习它 - 这是最后的错误之一。

DDL代码：

<asp:Panel ID="Panel1" runat="server" CssClass="form-field-container">
  <asp:Label ID="Label19" runat="server" CssClass="form-label"
  AssociatedControlID="ddlManufacturer">
    Manufacturer
    <asp:Label runat="server" CssClass="form-field-required-indicator" Text="*" />
  </asp:Label>
  <asp:RequiredFieldValidator ID="RequiredFieldValidator1" 
    runat="server" ControlToValidate="ddlManufacturer" InitialValue="-1" 
    Display="Dynamic" Text="Required" ErrorMessage="Manufacturer is Required" 
    CssClass="form-validator">
  </asp:RequiredFieldValidator>
  <asp:DropDownList ID="ddlManufacturer" runat="server" CssClass="form-data" AutoPostBack="True">
    <asp:ListItem Selected="True" Text="-- Select --" Value="-1"></asp:ListItem>   
  </asp:DropDownList>
</asp:Panel>
<asp:Panel ID="Panel2" runat="server" CssClass="form-field-container">
  <asp:Label ID="Label6" runat="server" CssClass="form-label"
    AssociatedControlID="txtDescription">
      Description
  </asp:Label>
  <br />
  <asp:TextBox ID="txtDescription" runat="server" CssClass="form-data" />
</asp:Panel>

背后的代码：

- Page_Load组件

我不确定为什么最后一位开发人员对此进行了注释：

protected void Page_Load(object sender, EventArgs e) {
  Instantiate();
  //if (!IsPostBack) { // initial load
  //} else { //  post back
  //}
}

- 参考的完整页码

public partial class ManufacturerModelFormUserControl : System.Web.UI.UserControl {
  public delegate void FormActionEventHandler(string action);
  public event FormActionEventHandler ActionPerformed;
  public event PageNotificationEventHandler PageNotification;
  private GuiUtility _guiUtil;

  private User _currentUser { 
    get {
      object o = Session["CurrentUser"];
      return (o == null) ? new User() : (User) Session["CurrentUser"];
    }

    set {
      Session["CurrentUser"] = value;
    }
  }

  private ManufacturerModel _manufacturerModel { 
    get {
      object o = ViewState["ManufacturerModel"];
      return (o == null) ? new ManufacturerModel() : (ManufacturerModel)
        ViewState["ManufacturerModel"];
    }

    set {
      ViewState["ManufacturerModel"] = value;
    }
  }

  public void NewManufacturerModel() {}

  public void LoadManufacturerModel(int id) {
     if (id <= 0) {
       return;
     }

     _manufacturerModel = ManufacturerModelAdapter.GetById(id);

     if (_manufacturerModel.ManufacturerModelId > 0) {
       this.Visible = true;
     }
   }

   public bool Save() {
     bool bIsSaved = false;
     if (!ValidateForm()) {
       return false;
     }

     PopulateObjectsFromForm();
     _manufacturerModel = ManufacturerModelAdapter.Save(_manufacturerModel, _currentUser);

     if (_manufacturerModel.ManufacturerModelId != 0) {
       bIsSaved = true;
     } else { 
       //problem occurred
       RaisePageNotificationEvent(new PageNotification(PageNotificationType.Error, "Model Number could not be saved"));
       return false;
     }

     if (bIsSaved) {
       RaiseActionEvent("Save");
       RaisePageNotificationEvent(new PageNotification(PageNotificationType.Generic, String.Format("Model Number Saved: {0}", _manufacturerModel.ModelNumber)));                 
     }

     ClearForm(); 
     return bIsSaved;
   }

   public void Cancel() {
     ClearForm();
     RaiseActionEvent("Cancel");
     RaisePageNotificationEvent(new PageNotification(PageNotificationType.Generic, "Action Cancelled"));
   }

   protected void Page_Load(object sender, EventArgs e) {
     Instantiate();
     // if (!IsPostBack) { 
     //   initial load
     // } else { 
     //  post back
     // }
   }

   private void Instantiate() {
     _guiUtil = new GuiUtility();
     PopulateListControls();
     this.txtModelNumber.Focus(); 
   }

   private void PopulateListControls() {
     Dictionary<int, string> manufactuerers = ManufacturerAdapter.GetAllDictionary();
     ddlManufacturer.DataSource = manufactuerers;
     ddlManufacturer.DataTextField = "Value";
     ddlManufacturer.DataValueField = "Key";
     ddlManufacturer.DataBind();
   }

   private bool ValidateForm() {
      IValidator v;
      bool bIsValid = true;
      int vCount;

      Page.Validate(); 
      vCount = Page.Validators.Count;

      for (int i = 0; i < vCount; i++) { 
        v = Page.Validators[i];
        if (!v.IsValid) {
          RaisePageNotificationEvent(new PageNotification(PageNotificationType.Validation, v.ErrorMessage));
          bIsValid = false;
        }
      }

      /* *
      * Additional validation checks
      * */

      return bIsValid;
    }

    private void ClearForm() {
      _manufacturerModel = new ManufacturerModel();
      this.txtModelNumber.Text = "";
      this.txtDescription.Text = "";
      this.ddlManufacturer.SelectedIndex = -1;
    }

    private void PopulateForm(ManufacturerModel m) { 
      _guiUtil.ListControlSelectValueIfExists((ListControl) this.ddlManufacturer, m.Manufacturer.ManufacturerId.ToString());
      this.txtModelNumber.Text = m.ModelNumber;
      this.txtDescription.Text = m.Description;
    }

    private void PopulateObjectsFromForm() {
      ManufacturerModel m = new ManufacturerModel();
      m.ManufacturerModelId = _manufacturerModel.ManufacturerModelId; 
      m.Manufacturer = ManufacturerAdapter.GetById(Convert.ToInt32(this.ddlManufacturer.SelectedValue));
      m.ModelNumber = this.txtModelNumber.Text;
      m.Description = this.txtDescription.Text;

      _manufacturerModel = m;             
    }

    private void RaiseActionEvent(string action) {
      if (ActionPerformed != null) {
        ActionPerformed(action);
      }
    }

    private void RaisePageNotificationEvent(PageNotification pageNotification) {
      if (PageNotification != null) {
        PageNotification(pageNotification);
      }
    }

    protected void btnSave_Click(object sender, EventArgs e) {
      Save();
    }

    protected void btnCancel_Click(object sender, EventArgs e) {
      Cancel();
    }
  }
}

Answer 1

每次回发都会填充DropDownList，因此您将松开所选值。将实例化移动到if（！Page.IsPostBack）块内：

if (!IsPostBack) { 
    //initial load
   Instantiate();
}

Answer 2

只是为将来的观众提供一些额外的资源，这里是已解决的更新代码：

 protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            { 
                Instantiate();
            }
        }

数据输入的下拉列表只会在列表中写入第一个值，无论选择什么

2 个答案: