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c# - 覆盖 ASP.NET Boundfield 以支持 Dropdownlist 缺少最后一项功能

转载 作者:太空宇宙 更新时间:2023-11-03 11:51:39 24 4
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如果我将它放在 Gridview 中,我设法覆盖 Boundfield 以显示下拉列表。

protected override void InitializeDataCell(DataControlFieldCell cell, DataControlRowState rowState)
{
Control child = null;
Control cellControl = null;

if ((((rowState & DataControlRowState.Edit) != DataControlRowState.Normal) && !this.ReadOnly)
|| ((rowState & DataControlRowState.Insert) != DataControlRowState.Normal))
{
// If data cell is in edit mode, create DropDownList editor for this cell
// and set data properties.

DropDownList box = new DropDownList();
box.Items.Add(DefaultValueText);

box.DataSource = this.GetDataSource();
box.DataMember = this.BusinessObjectName;
box.DataTextField = this.DataTextField;
box.DataValueField = this.DataValueField;
box.AppendDataBoundItems = true;
box.ToolTip = this.HeaderText;

cell.Controls.Add(box);
box.DataBind();
// if in edit mode, prepare dropdown for binding
if ((this.DataField.Length != 0) && ((rowState & DataControlRowState.Edit) != DataControlRowState.Normal))
{
cellControl = box;
}
}
else if (this.DataField.Length != 0) // if in read only mode, prepare cell for binding
{
cellControl = cell;
}

if ((cellControl != null) && base.Visible)
{
cellControl.DataBinding += new EventHandler(this.OnDataBindField);
}
}


protected override void OnDataBindField(object sender, EventArgs e)
{
Control control = (Control)sender;
Control namingContainer = control.NamingContainer;
object dataValue = this.GetValue(namingContainer);
bool encode = (this.SupportsHtmlEncode && this.HtmlEncode) && (control is TableCell);
string str = this.FormatDataValue(dataValue, encode);
if (control is TableCell)
{
if (str.Length == 0)
{
str = " ";
}
((TableCell)control).Text = str;
}
else
{
//If data cell is in edit mode, set selected value of DropDownList
if (dataValue != null)
{
DropDownList dropDownList = (DropDownList) control;

ListItem itm = dropDownList.Items.FindByText(dataValue.ToString());
if (itm != null)
{
dropDownList.Text = itm.Value;
}
else
((DropDownList)control).Text = DefaultValueText;
}
}
}

我添加的最后一个功能是默认值/如果未选择任何内容则显示的附加项目,例如“请选择”。我可以通过 OnDataBind 事件中的属性 DefaultValueText 进行设置。

现在我面临的问题是:

在 InitializeDataCell 中,如果我设置

box.AppendDataBoundItems = true;

并调用

box.DataBind();

下拉列表包含所有项目以及附加的默认项目。它在 OnDataBind 事件中也能很好地工作,如果数据绑定(bind)项不包含值,我现在可以在其中选择默认值。

但是当下拉列表显示在 gridview 中时,它包含默认值加上数据源中的所有内容两次,因为我设置了 AppendDataBoundItems = true,这导致下拉列表在添加项目时不清除它的项目 gridview 必须调用数据绑定(bind)两次,但它只在 OnDataBind 事件方法中注册一次。我在那里只看到一个调用,在那一刻,一切都很好,下拉列表包含默认项加上数据源中的每个项目之一。

有什么建议可以在何处或如何处理数据绑定(bind),以便我可以完全控制数据绑定(bind)?

最佳答案

我设法让它工作

我将所有用于设置 selectedValue 的代码都移到了 DropDownList 的 DataBound 事件中。在这种情况下,数据绑定(bind)已经发生并且值列表可供我设置 selectedValue。我不再自己调用 DataBind,因为无论如何都会在控件上调用它。我只在开头添加“进行选择”项并将 AppendDataBoundItems 设置为 true。

现在在某些只读状态下可能存在未处理的情况,因为我不处理任何 Cell.Databinding() 事件。

为感兴趣的人提供完整的源代码......

它基于 Javad Zarrinabadi 的示例,地址为 CodeProjct

用法:

DropDownBoundField dropDownBoundField = new DropDownBoundField();
dropDownBoundField.HeaderText = "NyColumnName";
dropDownBoundField.BusinessObjectName = "BusinessLogic.MyDataClass";
dropDownBoundField.SelectMethod = "GetEnumerable";
dropDownBoundField.DataTextField = "Name"; // what should be displayed
dropDownBoundField.DataValueField = "Id"; // value behind the displayed text
dropDownBoundField.DataField = "IdProperty"; // Property to bind to
dropDownBoundField.DefaultValueText = "Select"; // text on first item as
default if DataField is null
dropDownBoundField.FindBy = SetSelectedValueBy.Value // Choose how the DataField is being evaluated, as source for the value or the text
GridView.Columns.Add(dropDownBoundField);

类:

 using System;
using System.Web.UI.WebControls;
using System.Web.UI;
using System.ComponentModel;
using System.Web;
using System.Collections.Specialized;

namespace IDVCode.GridViews
{
public class DropDownField : BoundField
{
#region fields
private string _listDataSourceID;
private string _listDataMember;
private string _listDataTextField;
private string _listDataValueField;
#endregion

#region eventHandler

protected override void InitializeDataCell(DataControlFieldCell cell, DataControlRowState rowState)
{
DropDownList dropDownList = new DropDownList();
dropDownList.ToolTip = HeaderText;
dropDownList.DataSourceID = ListDataSourceID;
dropDownList.DataMember = ListDataMember;
dropDownList.DataTextField = ListDataTextField;
dropDownList.DataValueField = ListDataValueField;
dropDownList.Enabled = !ReadOnly;
cell.Controls.Add(dropDownList);

if (rowState == DataControlRowState.Normal || rowState == DataControlRowState.Alternate || ReadOnly)
{
dropDownList.Enabled = false;
}
if (DataField.Length != 0) // && ((rowState & DataControlRowState.Edit) != DataControlRowState.Normal))
{
dropDownList.DataBound += new EventHandler(OnDataBindField);
}
}

protected override void OnDataBindField(object sender, EventArgs e)
{
Control control = (Control)sender;
Control namingContainer = control.NamingContainer;
object dataValue = GetValue(namingContainer);
bool encode = (SupportsHtmlEncode && HtmlEncode) && (control is TableCell);
string str = FormatDataValue(dataValue, encode);
if (control is TableCell)
{
if (str.Length == 0)
{
str = " ";
}
((TableCell)control).Text = str;
}
else
{
if (!(control is DropDownList))
{
throw new HttpException("BoundField_WrongControlType");
}
if (((DropDownList)control).Items.Count > 0) // Don't call selectedValue if empty
{
if (dataValue != null)
{
DropDownList dropDownList = (DropDownList)control;

ListItem item = null;
if (FindBy == SetSelectedValueBy.Value)
{
item = dropDownList.Items.FindByValue(dataValue.ToString());
}
else
{
item = dropDownList.Items.FindByText(dataValue.ToString());
}

if (item != null)
dropDownList.Text = item.Value;
else
{
ListItem defaultItem = dropDownList.Items.FindByText(DefaultValueText);
if (defaultItem != null)
dropDownList.SelectedValue = defaultItem.Value;
}
}
}
}
}

public override void ExtractValuesFromCell(IOrderedDictionary dictionary, DataControlFieldCell cell,
DataControlRowState rowState, bool includeReadOnly)
{
Control control = null;
string dataField = DataField;
object text = null;
string nullDisplayText = NullDisplayText;
if (((rowState & DataControlRowState.Insert) == DataControlRowState.Normal) || InsertVisible)
{
if (cell.Controls.Count > 0)
{
control = cell.Controls[0];
DropDownList box = control as DropDownList;
if (box != null)
{
text = box.SelectedValue;
}
}
else if (includeReadOnly)
{
string s = cell.Text;
if (s == " ")
{
text = string.Empty;
}
else if (SupportsHtmlEncode && HtmlEncode)
{
text = HttpUtility.HtmlDecode(s);
}
else
{
text = s;
}
}
if (text != null)
{
if (((text is string) && (((string)text).Length == 0)) && ConvertEmptyStringToNull)
{
text = null;
}
if (((text is string) && (((string)text) == nullDisplayText)) && (nullDisplayText.Length > 0))
{
text = null;
}
if (dictionary.Contains(dataField))
{
dictionary[dataField] = text;
}
else
{
dictionary.Add(dataField, text);
}
}
}
}

#endregion

#region Properties

public virtual string ListDataSourceID
{
get
{
if (_listDataSourceID == null)
{
object stateBag = ViewState["ListDataSourceID"];
if (stateBag != null)
{
_listDataSourceID = (string)stateBag;
}
else
{
_listDataSourceID = string.Empty;
}
}
return _listDataSourceID;
}
set
{
if (!object.Equals(value, ViewState["ListDataSourceID"]))
{
ViewState["ListDataSourceID"] = value;
_listDataSourceID = value;
OnFieldChanged();
}
}
}

public virtual string ListDataMember
{
get
{
if (_listDataMember == null)
{
object stateBag = ViewState["ListDataMember"];
if (stateBag != null)
{
_listDataMember = (string)stateBag;
}
else
{
_listDataMember = string.Empty;
}
}
return _listDataMember;
}
set
{
if (!object.Equals(value, ViewState["ListDataMember"]))
{
ViewState["ListDataMember"] = value;
_listDataMember = value;
OnFieldChanged();
}
}
}

public virtual string ListDataTextField
{
get
{
if (_listDataTextField == null)
{
object stateBag = ViewState["ListDataTextField"];
if (stateBag != null)
{
_listDataTextField = (string)stateBag;
}
else
{
_listDataTextField = string.Empty;
}
}
return _listDataTextField;
}
set
{
if (!object.Equals(value, ViewState["ListDataTextField"]))
{
ViewState["ListDataTextField"] = value;
_listDataTextField = value;
OnFieldChanged();
}
}
}

public virtual string ListDataValueField
{
get
{
if (_listDataValueField == null)
{
object stateBag = ViewState["ListDataValueField"];
if (stateBag != null)
{
_listDataValueField = (string)stateBag;
}
else
{
_listDataValueField = string.Empty;
}
}
return _listDataValueField;
}
set
{
if (!object.Equals(value, ViewState["ListDataValueField"]))
{
ViewState["ListDataValueField"] = value;
_listDataValueField = value;
OnFieldChanged();
}
}
}

[Description("Sets a default value if applicable")]
[Category("Appearance")]
public string DefaultValueText
{
get
{
object val = ViewState["DefaultValueText"];
if (val != null)
{
return (string)val;
}
return (string.Empty);
}

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

[Description("Defines how the SelectedValue is set")]
[Category("Data")]
[DefaultValue(SetSelectedValueBy.Value)]
public SetSelectedValueBy FindBy
{
get
{
object val = ViewState["SetSelectedValueBy"];
return val != null ? (SetSelectedValueBy) val : SetSelectedValueBy.Value;
}
set
{
ViewState["SetSelectedValueBy"] = value;
}
}

public enum SetSelectedValueBy
{
Text,
Value
}

#endregion
}

关于c# - 覆盖 ASP.NET Boundfield 以支持 Dropdownlist 缺少最后一项功能,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/1979381/

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