下拉列表选择的值不起作用

Question

In my ASP.NET project. I have two dropdownlist and a checkbox. When the checkbox is checked, the selected value of DropDownList1 must be same as selcted value of the DropDownList2 . But the DropDownList1.SelectedValue is not working.

Here is my code:

protected void chkSameBAddress_CheckedChanged(object sender, EventArgs e)
{
    try
    {
        if (this.chkSameBAddress.Checked == true)
        {

          this.txtcSAddress1.Text=  this.txtcBAddress1.Text;
          this.txtcSAddress2.Text = this.txtcBAddress2.Text;
          this.txtcSAddress3.Text = this.txtcBAddress3.Text;
          this.txtcSAddress4.Text = this.txtcBAddress4.Text;
          this.txtcSCity.Text = this.txtcBCity.Text;
          this.txtcSPostCode.Text = this.txtcBPostCode.Text;
          this.txtcSState.Text = this.txtcBState.Text;

          this.ddlcSCountry.Items.FindByValue(ddlcBCountry.SelectedItem.Value).Selected = true;


        }

    }
    catch (Exception ex)
    {
        logger.Error(ex.Message);
        throw;

    }
}

As seen in the example above, if chkSmaeBAddress is checked then the selected value of ddlcSCountry must be same as ddlcBCountry selected value.

Answer 1

Where are you binding data to these dropdown list controls? They should be bound only in the initial loading of the page as follows. I suspect that you are binding them in every page load and therefore selected values disappear.

protected void Page_Load(object sender, EventArgs e)
{

    if (!Page.IsPostBack)
    {
        //Please check if you are binding checkbox controls here. 
        //If not bring them in here
    }
}

Other condition is that both ddlcSCountry and ddlcBCountry hould have same values to be able to select. Otherwise ddlcSCountry.Items.FindByValue(ddlcBCountry.SelectedItem.Value) will be null and will throw an error when trying to set the Selected property

If both above conditions are okay, your code should work.

EDIT Sorry, my commented code should be to check binding of dropdown list controls not the checkbox. so it should be as

//Please check if you are binding both dropdown list controls here. 
//If not bind them within the if (!Page.IsPostBack)

Put a breakpoint in your if (this.chkSameBAddress.Checked == true) line within CheckedChanged event and see it is executing and then the runtime values...

Answer 2

Surely you are trying to make the dropdown boxes equal?

use

ddlcSCountry.SelectedIndex = ddlcSCountry.FindStringExact(ddlcBCountry.Text);

This will select the matching option in the list and not just set the text in the field, which is very useful when you have underlying values with your text options.

Answer 3

The accepted solution is an obvious solution to the most common cause, however, there is one more surprising issue that can cause this!

My list values came from a database and the values had linefeed and carriage return from the database values: \\r\\n . These values look like an innocent space, but actually they are not!

My solution was to remove these hidden Char values. Hope it helps.

Answer 4

Try this for select

ddlcSCountry.Text=ddlcBCountry.SelectedItem.Value;

It will selected needed item

Answer 5

Make sure that chkSameBAddress.AutoPostBack is set to true. If it is set and still doesn't work, consider using an UpdatePanel control or moving that logic to the client using JavaScript.

Answer 6

确保在DropDownList的属性中将AutoPostBack设置为true。

Answer 7

我只是切换到使用<select runat="server" id="test1"></Select>我只需稍微修改后面的代码就可以了。