asp.net c# 防止从服务器端代码更改索引时触发 selectedindexchanged 事件

Question

我在与

相同的 aspx 页面上有两个下拉列表控件

<asp:DropDownList ID="ddlM" runat="server" Width="123px" AutoPostBack="True" OnSelectedIndexChanged="ddlM_SelectedIndexChanged">
</asp:DropDownList>

<asp:DropDownList ID="ddlC" runat="server" Width="123px" AutoPostBack="True" OnSelectedIndexChanged="ddlC_SelectedIndexChanged">
</asp:DropDownList>

两者的 OnSelectedIndexChanged 的​​ C# 代码如下：

protected void ddlC_SelectedIndexChanged(object sender, EventArgs e)
{
   ddlM.SelectedIndex = 0;
   ViewState["ddlC"] = true;
   ViewState["ddlM"] = false;                 
   BindPGrid();            
}

protected void ddlM_SelectedIndexChanged(object sender, EventArgs e)
{
   ddlC.SelectedIndex = 0;                
   ViewState["ddlC"] = false;
   ViewState["ddlM"] = true; 
   BindPGrid();
}

两者都使用一些服务器端代码由数据库记录项填充。现在，“ddlM”的 OnSelectedIndexChanged 事件我想选择“ddlC”的第一个索引，但不触发事件 ddlC_SelectedIndexChanged。对于“ddlC”，与“ddlC”的 OnSelectedIndexChanged 事件相同，我想选择“ddlM”的第一个索引，但不触发事件 ddlM_SelectedIndexChanged。不对，它会触发事件。我该怎么做才能防止它？

谢谢

Answer 1

或者，您可以从控件中删除并重新添加 SelectedIndexChanged 事件处理程序

 ddlM.SelectedIndexChanged -= ddlM_SelectedIndexChanged;

 ddlM.SelectedIndex = 0;
 ViewState["ddlC"] = false;
 ViewState["ddlM"] = true; 
 BindPGrid();

 ddlM.SelectedIndexChanged += ddlM_SelectedIndexChanged;

那么你就不必乱用全局标志了

Answer 2

在这种情况下，我们创建一个全局bool 标志并将其值设置为true，然后再更改SelectedIndexChanged。在另一个控件的SelectedIndexChanged 中检查其值是否为真。如果为真，我们将它返回到事件之外。并在外面时再次更改标志值。确保始终将标志值更改回 false，否则如果该事件由同一控件生成，它将永远不会触发。

boool flag = false;

protected void ddlC_SelectedIndexChanged(object sender, EventArgs e)
{
   flag = true;
   ddlM.SelectedIndex = 0;
   flag = false;
   ViewState["ddlC"] = true;
   ViewState["ddlM"] = false;                 
   BindPGrid();            
}

protected void ddlM_SelectedIndexChanged(object sender, EventArgs e)
{
   if(flag)
       return;

   ddlC.SelectedIndex = 0;                
   ViewState["ddlC"] = false;
   ViewState["ddlM"] = true; 
   BindPGrid();
}

或者您可以删除事件处理程序，如

protected void ddlC_SelectedIndexChanged(object sender, EventArgs e)
{
   ddlM.SelectedIndexChanged -= ddlM_SelectedIndexChanged;
   ddlM.SelectedIndex = 0;
   ddlM.SelectedIndexChanged += ddlM_SelectedIndexChanged;
   ViewState["ddlC"] = true;
   ViewState["ddlM"] = false;                 
   BindPGrid();            
}