Combobox and SelectionChanged problem

Question

I'm trying to check for a value in my combobox, but it fails, my value is never matched and I have this warning :

Possible unintended reference comparison; to get a value comparison, cast the left hand side to type 'string'

private void comboBox1_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {

        if (((ComboBox)sender).SelectedValue == "Floyd-Warshall")
        {
            MessageBox.Show("foobar");

Thanks.

Answer 1

There are various ways to fix, one if to cast to a string, the other is to call ToString on the SelectedValue.

As you have stated that some of the other suggested answers do not work, are you sure the item in the Combobox is in fact a string?

For example, this will work with the fixes suggested:

<Window x:Class="ExerciseOne.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525" xmlns:extern="clr-namespace:System;assembly=mscorlib">
    <Grid>
    <ComboBox SelectionChanged="ComboBox_SelectionChanged">
        <ComboBox.Items>
                <extern:String>Hello</extern:String>
                <extern:String>Floyd-Warshall</extern:String>
            </ComboBox.Items>
    </ComboBox>
    </Grid>
</Window>

But this won't:

<Window x:Class="ExerciseOne.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525" xmlns:extern="clr-namespace:System;assembly=mscorlib">
    <Grid>
    <ComboBox SelectionChanged="ComboBox_SelectionChanged">
        <ComboBox.Items>
                <ComboBoxItem>Hello</ComboBoxItem>
                <ComboBoxItem>Floyd-Warshall</ComboBoxItem>
            </ComboBox.Items>
    </ComboBox>
    </Grid>
</Window>

You can quickly determine if this is the case by running the following code in your existing event handler:

   MessageBox.Show(((ComboBox)sender).SelectedValue.GetType().ToString());

Answer 2

SelectedValue's type is object so, even it matches the value the equal operation will return false, so you have to compare string with string instead like the following:

    if (((ComboBox)sender).SelectedValue.ToString() == "Floyd-Warshall")