How to set the selecteditem

问题

I am trying to set the value/selecteditem of a listpicker control - from the silverlight toolkit for windows phone 7 (when the user wants to edit an entry in xml, it pulls the data out of IO and sets it in the text boxes/listpickers).

I am currently trying to use:

ListPickerSub.SelectedItem = sub;

(sub is a string)

But it is throwing a System.InvalidOperationException

Additional information: SelectedItem must always be set to a valid value.

回答1:

SelectedItem is expecting a ListPickerItem (which is one of the items in the list). You're passing it a string - hence the error.

You may find it easier to set the SelectedIndex.

It's hard to give a relevant example of setting the SelectedItem without knowing what you're populating the list with.

Edit:
Here's an example of how you could bind to strings. Without a workable example of what you are actually binding to the itemsource this is hte best I can do. (Just giving the name of the object or partial code isn't enough.)

Assuming:

<Controls:ListPicker x:Name="ListPickerSub">
    <Controls:ListPicker.ItemTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding}" />
        </DataTemplate>
    </Controls:ListPicker.ItemTemplate>
    <Controls:ListPicker.FullModeItemTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding}" />
        </DataTemplate>
    </Controls:ListPicker.FullModeItemTemplate>
</Controls:ListPicker>

Then I can bind the contents with:

ListPickerSub.ItemsSource = SubItems();


private IEnumerable<string> SubItems()
{
    yield return "monday";
    yield return "tuesday";
    yield return "wednesday";
    yield return "thursday";
    yield return "friday";
    yield return "saturday";
    yield return "sunday";
}

and set the SelectedItem with:

ListPickerSub.SelectedItem = "sunday";

回答2:

Something like the following:

ListPickerSub.SelectedItem = ListPickerSub.Items.First(x => (x as ListPickerItem).Content.ToString() == sub);

You may need to cast the Content to TextBlock, and change the code accordingly. The above works for my case where ListPicker is populated dynamically using ListPickerItem.

回答3:

Surely you want to set the data in the underlying datasource and then just refresh your list?

来源：https://stackoverflow.com/questions/4418754/how-to-set-the-selecteditem

标签

silverlight

windows-phone-7

silverlight-toolkit