在WPF中未设置组合框的选定文本

Question

I have a WPF app with a combobox that is bound to a database call. The user types a name, and the database call returns the possible name matches. I check the length of the typed text to make sure at least 4 characters have been typed to increase speed.

The issue i have is that after the database call returns its result, the text in the combobox is selected. The user continues to type at this point they overwrite the selected text. I tried many things, but setting the selected index in code-behind gives partial results. initially it doesn't work but subsequent searches the text is not selected. Ideally i would like to set something like selectionLength = 0 but it isn't available to me.

My question is how do i stop the combobox text already entered from becoming selected?

the xaml extract:

<ComboBox 
            Grid.Column="2" 
            Grid.Row="1" 
            Height="30" 
            IsEditable="True"
            IsReadOnly="False"
            ItemsSource="{Binding PatientsCollection,UpdateSourceTrigger=PropertyChanged,NotifyOnTargetUpdated=True}"
            Name="SelectPatientCombobox" 
            SelectedValue="{Binding SelectedPatientId,Mode=Default}"
            SelectedValuePath="pat_pharmacy_patient_id" 
            TargetUpdated="SelectPatientCombobox_TargetUpdated"
            Text="{Binding SearchPatientText, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
            VerticalAlignment="Top"
            Visibility="{Binding SelectPatientVisible, Converter={StaticResource BoolToVis}}"
            >
            <ComboBox.ItemTemplate>
                <DataTemplate>
                    <Grid Margin="0,0,0,0">
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="Auto" />
                            <ColumnDefinition Width="Auto" />
                        </Grid.ColumnDefinitions>
                        <Grid.RowDefinitions>
                            <RowDefinition Height="Auto" />
                            <RowDefinition Height="Auto" />
                        </Grid.RowDefinitions>
                        <Image Source="{Binding Path=PatientIcon}" MaxHeight="32" MaxWidth="32" Margin="0,2,5,2"
                           Grid.Column="0" Grid.RowSpan="2" />
                        <TextBlock Grid.Row="0" Grid.Column="1">
                        <Run Text="{Binding TitleFirstName, Mode=OneWay}" />
                        <Run Text=" " />
                        <Run FontWeight="Bold" Text="{Binding pat_name_last}" />
                        </TextBlock>
                        <StackPanel Grid.Row="1" Orientation="Horizontal" Grid.Column="1">
                            <TextBlock Foreground="SlateGray" Text="{Binding cod_addr1}" Margin="0,0,5,0" />
                            <TextBlock Foreground="SlateGray" Text="{Binding suburb}" Margin="0,0,5,0" />
                            <TextBlock Foreground="SlateGray" Text="{Binding postcode}" Margin="0,0,0,0" />
                        </StackPanel>
                    </Grid>
                </DataTemplate>
            </ComboBox.ItemTemplate>
        </ComboBox>

the code behind:

        private void SelectPatientCombobox_TargetUpdated(object sender, DataTransferEventArgs e)
    {
        if ( false == ((ComboBox) sender).IsLoaded) return;
        ((ComboBox) sender).IsDropDownOpen = ((ComboBox) e.Source).Items.Count > 0;
        ((ComboBox)sender).SelectedIndex = -1;
    }

The ViewModel complicated when the database call returns data it converts it to an ObservableCollection

Answer 1

answering this if someone else has the same issue. This is a hack, but i couldn't work out a better way to fix the issue properly.

In the code-behind i programmatically press the right arrow key to make the text not selected. There is a slight blip of the screen where you can see the the text being unselected, but it works.

so the code behind becomes:

    private void SelectPatientCombobox_TargetUpdated(object sender, DataTransferEventArgs e)
    {
        if ( false == ((ComboBox) sender).IsLoaded) return;
        if ((ComboBox)sender == null) return;
        ((ComboBox) sender).IsDropDownOpen = ((ComboBox) e.Source).Items.Count > 0;
        ((ComboBox)sender).SelectedIndex = -1;

        // when the result is returned, the text is highlighted.
        // typing when text is selected erases the text already typed.
        // so this total hack is a way to press the right arrow key after the results
        // come back so that the text is no longer selected.

        const Key key = Key.Right; // Key to send
        var target = Keyboard.FocusedElement;    // Target element
        var routedEvent = Keyboard.KeyDownEvent; // Event to send
        var inputSource = PresentationSource.FromVisual((ComboBox)sender);

        target.RaiseEvent(
            new KeyEventArgs(
                    Keyboard.PrimaryDevice,
                    inputSource,
                    0,
                    key)
                { RoutedEvent = routedEvent }
        );
    }