WPF ToolTip does not update

Question

Assuming I have a simple class that represents a staff member

class Staff
{
    public string FirstName { get; set; }
    public string FamilyName { get; set; }
    public int SecondsAlive { get; set; }        
}

and I have a DataTemplate for staff

<DataTemplate DataType={x:Type Staff}>
    <StackPanel Orientation="Horizontal">
        <TextBlock Text={Binding FirstName}/>
        <TextBlock Text=" ">
        <TextBlock Text={Binding FamilyName}/>
        <StackPanel.ToolTip>
            <TextBlock Text={Binding SecondsAlive}/>
        </StackPanel.ToolTip>
     </StackPanel>
</DataTemplate>

I then show a whole bunch of staff in a ListBox

myListBox.ItemsSource = GetAllStaff();

Pretty standard stuff. The problem I have is that the tooltip which shows the number of seconds that someone has been alive does not get updated. When you first mouse over a staff member then it works fine but from then on it keeps that value for ever. I could implement INotifyPropertyChanged to get around this but it seems like overkill to do this for every staff member whenever SecondsAlive changes. Say I have 400 staff in the list then I have to raise 400 events even though the user might never look at another tooltip. What I would like is to make the tooltip request the SecondsAlive property ever time it is shown. Is that possible?

Please note that this is just an example and I don't need to know how many seconds my staff have been alive :-) But I have the same issue that I need to raise an even around 400 times just for a tooltip which someone probably won't look at.

Answer 1

In this particular case there is a cool trick you can use

Seconds Alive Now = Seconds Alive originally + Elapsed Time

You can bind to the Elapsed Time property and specify a converter that adds the initial value to it. That way you only need to raise 1 event and the tooltips would all be updated.

Edit: You can add the ElapsedTime property (with INotifyPropertyChanged) to many places -- one logical place could be to the collection that is storing your Staff objects

Edit: You would also need to bind each tooltip to the shared ElapsedTime property rather than the SecondsAlive property

Answer 2

This example shows how to add a tooltip to a grid that recalculates the tooltip on demand, when the user hovers over a cell in the grid.

This is useful if you have a huge grid with 10,000 items, and you want to update the grid continuously - but you don't want to update the tooltips continuously, as this is time consuming.

This example is for Infragistics, but the principle applies equally to other fine libraries such as DevExpress.

Xaml

<ig:TemplateColumn Key="ColumnKey">
    <ig:TemplateColumn.HeaderTemplate>
        <DataTemplate>
            <TextBlock Text="Header"></TextBlock>
        </DataTemplate>
    </ig:TemplateColumn.HeaderTemplate>
    <ig:TemplateColumn.ItemTemplate>
        <DataTemplate>
            <StackPanel HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
                <StackPanel.ToolTip>
                    <TextBlock Text="{Binding ToolTip}"/>
                </StackPanel.ToolTip>
                <i:Interaction.Triggers>
                    <i:EventTrigger EventName="MouseEnter" >
                        <i:InvokeCommandAction Command="{Binding ToolTipHoverRefreshCommand}" />
                    </i:EventTrigger>
                </i:Interaction.Triggers>
            </StackPanel>
        </DataTemplate>
    </ig:TemplateColumn.ItemTemplate>
</ig:TemplateColumn>

ViewModel

public ICommand ToolTipHoverRefreshCommand => new DelegateCommand(() =>
{
    this.OnPropertyChanged(this.ToolTip);
});  

public string ToolTip
{
    get
    {
        return DateTime.Now.ToString();
    }
    set
    {
        this.OnPropertyChanged(nameof(this.ToolTip));
    }
}

Answer 3

OMG!!! I have finally found the solution to this problem!!! This has been bugging me for months. I'm not surprised no one answered this because the code I typed out at the top actually DIDN'T show the problem I was trying to reproduce, in fact it showed the solution. The answer is that if you define your tooltip like this

    <StackPanel.ToolTip>
        <TextBlock Text="{Binding SecondsAlive}"/>
    </StackPanel.ToolTip>

Then everything works just fine and dandy and there is no need to raise a propertyChanged event on "SecondsAlive". The framework will call the SecondsAlive property every time the tooltip is shown. The problem comes when you define your tooltip like this:

    <StackPanel.ToolTip>
        <ToolTip>
            <TextBlock Text="{Binding SecondsAlive}"/>
        </ToolTip>
    </StackPanel.ToolTip>

Having the extra tooltip tag in there makes sense, surely you need to create a tooltip object to assign it to the tooltip property but this is incorrect. What you are assigning to the tooltip property is actually the content of the tooltip. I was assuming you needed to give it controls such as textblock and image to display but you can pass in anything and it will display the content just like a content control. Seeing it inherits from content control this makes sense :-) It all seems obvious once you know :-)

Thanks everyone for looking at this.

PS. I found an additional problem in that the next logical step in simplifying code is to just assign text straight to the tooltip like this (assuming your tooltip is plain text):

 <TextBlock Text="{Binding Path=StaffName}" ToolTip="{Binding Path=StaffToolTip}"/>

This also causes the original problem I was having. This makes sense because the results of the property StaffToolTip get assigned to the tooltip property and never get called again. However, it doesn't quite make sense why then assigning a TextBlock to the tooltip property actually solves the problem.

Answer 4

It's worth noting that the ToolTip appears to check your object that it's bound to for equality before reloading itself with the new data.

In my case I did an override of

public override bool Equals(object obj) 

and

public override int GetHashCode()

on a class with properties

public class MultipleNameObject { string Name, string[] OtherNames};

Unfortunatley I only did a string.Compare() on the Name property of the MultipleNameObject for equality purposes. The tool tip was supposed to display OtherNames in a ItemsControl, but was not updating if Name was equal on the previous MultipleNameObject that the mouse hovered been over on the grid, even if the OtherNames were different.

[edit] Running with debug enabled confirms that the GetHashCode() override of my object was being used by the ToolTip to decide whether to grab the new data back. Fixing that to take the string[] OtherNames into account fixed the problem.