在 DataBind 上选择封装的 DropDownList 中的项目
我有一个复杂的 UserControl ，其主要目的是使用许多属性封装 DropDownList 以进行高级操作。
根据之前设置的属性，在 PreRender 事件上填充列表：
protected void Page_PreRender(object sender, EventArgs e)
{
sourceClient.SelectCommand = this.Property1 ? "exec a" : "exec b";
}
最常用的属性是 ClientID：
[Category("Settings")]
public int ClientID
{
get
{
return Int32.Parse(DropDownList1.SelectedItem.Value);
}
set
{
DropDownList1.Items.FindByValue(value).Selected = true;
}
}
Getter 通常由 SqlDataSources 中的 ControlPameters 调用> 在带有此控件的页面上。
Setter - 来自标记：
所以问题是：
为什么 Bind 中的 setter 比 PreRender 更早被调用？并且 DropDownList 为空，项目选择不起作用！如何解决此行为？
Edit1：好的，不是 PreRender 而是 Init。但是 DropDownList1_DataBinding 仍在属性设置器之后被调用！
I have a complex UserControl with the main purpose to encapsulate DropDownList with a number of properties for advanced manipulation.
List is being populated on PreRender event depending on properties previously were set:
protected void Page_PreRender(object sender, EventArgs e)
{
sourceClient.SelectCommand = this.Property1 ? "exec a" : "exec b";
}
The most used property is ClientID:
[Category("Settings")]
public int ClientID
{
get
{
return Int32.Parse(DropDownList1.SelectedItem.Value);
}
set
{
DropDownList1.Items.FindByValue(value).Selected = true;
}
}
Getter commonly is being called by ControlPameters in SqlDataSources on pages with this control.
Setter - from markup: <uc:UserControl1 runat="server" ClientID='<%# Bind("ID") %>' />.
So the question is:
Why does setter from Bind is called earlier then PreRender? And DropDownList is empty and item selecting doesn't work! How to workaround this behavior?
Edit1: Ok, not PreRender but Init. But DropDownList1_DataBinding is still being called after property setter!
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数据绑定始终发生在
PreRender之前。来自 ASP.Net 页面生命周期：解决您的问题的一种方法是仅处理
DataBinding事件并预先绑定您的下拉列表（甚至只是在Load期间执行），而不是等待一直到PreRender。这将确保 Bind 调用结束时DropDownList可用。另一种解决方案是仅将控件传递给数据源本身的引用，而不是使用 Bind 调用。然后，它可以在正确的时间以编程方式处理自身绑定 - 您可以加载
DropDownList，然后获取它的 ID，这一切都在PreRender期间通过访问数据源进行。DataBinding always occurs before
PreRender. From ASP.Net Page Lifecycle:One solution to your issue would be to just handle the
DataBindingevent and pre-bind your dropdownlist (or even just do it duringLoad), rather than waiting all the way untilPreRender. This would ensure that theDropDownListwas available when the Bind call goes off.Another solution would be to just pass your control a reference to the datasource itself, rather than using a Bind call. Then it could programmatically deal with binding itself at the right times - you could load your
DropDownList, and then get your ID for it, all duringPreRender, by accessing the datasource.