CODEWITHSUNDEEP
c#wpf
Jason Axelrod
Jason Axelrod

Reputation: 7805

Drag and Drop TabItems in WPF?

So I found this answered questions: Is it possible to rearrange tab items in tab control in wpf?

Using the information in that thread, I set it all up in my application:

<TabControl x:Name="tabControl">
    <TabControl.Resources>
        <Style TargetType="TabItem">
            <Setter Property="AllowDrop" Value="True"/>
            <EventSetter Event="PreviewMouseMove" Handler="TabItem_Drag"/>
            <EventSetter Event="Drop" Handler="TabItem_Drop"/>
        </Style>
    </TabControl.Resources>
</TabControl>

And the code:

private void TabItem_Drag(object sender, MouseEventArgs e)
{
    var tabItem = e.Source as TabItem;

    if (tabItem == null)
        return;

    if (Mouse.PrimaryDevice.LeftButton == MouseButtonState.Pressed)
        DragDrop.DoDragDrop(tabItem, tabItem, DragDropEffects.All);
}
private void TabItem_Drop(object sender, DragEventArgs e)
{
    var tabItemTarget = e.Source as TabItem;
    var tabItemSource = e.Data.GetData(typeof(TabItem)) as TabItem;

    if (!tabItemTarget.Equals(tabItemSource))
    {
        int sourceIndex = tabControl.Items.IndexOf(tabItemSource);
        int targetIndex = tabControl.Items.IndexOf(tabItemTarget);

        tabControl.Items.Remove(tabItemSource);
        tabControl.Items.Insert(targetIndex, tabItemSource);

        tabControl.Items.Remove(tabItemTarget);
        tabControl.Items.Insert(sourceIndex, tabItemTarget);

        tabControl.SelectedIndex = targetIndex;
    }
}

The problem is, when I drop the tab, I get the following error at

    if (!tabItemTarget.Equals(tabItemSource))

An exception of type 'System.NullReferenceException' occurred in Scoreboard Assistant.exe but was not handled in user code

Additional information: Object reference not set to an instance of an object.

When I click continue, I get the following error at

        DragDrop.DoDragDrop(tabItem, tabItem, DragDropEffects.All);

An unhandled exception of type 'System.NullReferenceException' occurred in PresentationCore.dll

Additional information: Object reference not set to an instance of an object.

And then the program dies. What am I doing wrong?

* EDIT *

Okay, I figured out what the issue is; I just need help fixing it. If the tab item is created as follows it works perfectly fine:

<TabItem Header="TabItem"/>

However, my tabs are being created as follows:

<TabItem>
    <TabItem.Header>
        <StackPanel Orientation="Horizontal">
            <Image Source="images/text.png" />
            <TextBlock Text="Text"/>
        </StackPanel>
    </TabItem.Header>
</TabItem>

As you can see, I am using a stackpanel to have an icon in the tab header. The problem seems to be that when I drag and drop the panel, instead of the e.Source being read as the tabitem, its reading the textblock within the stackpanel of the tabitem. How would I fix this?

Upvotes: 2

Views: 8361

Answers (1)

Dennis
Dennis

Reputation: 37770

Since the visual tree of TabItem header can be rather complex, you can't guarantee, that drop target will be a TabItem instance (that's what happening in your code).

But you can find TabItem via exploring visual tree:

private TabItem GetTargetTabItem(object originalSource)
{
    var current = originalSource as DependencyObject;            

    while (current != null)
    {
        var tabItem = current as TabItem;
        if (tabItem != null)
        {
            return tabItem;
        }

        current = VisualTreeHelper.GetParent(current);
    }

    return null;
}

private void TabItem_Drop(object sender, DragEventArgs e)
{
    var tabItemTarget = GetTargetTabItem(e.OriginalSource);
    if (tabItemTarget != null)
    {
        var tabItemSource = (TabItem)e.Data.GetData(typeof(TabItem));
        if (tabItemTarget != tabItemSource)
        {
            // the rest of your code
        }
    }
}

Upvotes: 3

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