WPF tooltip Binding getting override when I set the tooltip from code-CodePudding

I have a User control and I bind the tooltip of that control into some object's property

                        <usercontrols:ucButton x:Name="xSaveCurrentBtn" ButtonType="ImageButton" ButtonFontImageSize="16" ButtonImageWidth="18" ButtonImageHeight="18" ButtonImageType="Save" Click="xSaveSelectedButton_Click" ButtonStyle="{StaticResource $ImageButtonStyle_Menu}" DockPanel.Dock="Right" HorizontalAlignment="Right" VerticalAlignment="Center" Margin="0,0,0,0">
                            <usercontrols:ucButton.ToolTip>
                                <ToolTip Content="{Binding ItemName, Mode=OneWay}" ContentStringFormat="Save {0}"/>
                            </usercontrols:ucButton.ToolTip>
                        </usercontrols:ucButton>

from the code I set the data context of the ucButton to be my object:

xSaveCurrentBtn.DataContext = WorkSpace.Instance.CurrentSelectedItem;

sometimes the CurrentSelectedItem is null, and if this is the case I want the tooltip to display "No Item Selected" I tried doing this:

xSaveCurrentBtn.Tooltip = "No Item Selected";

but when the CurrentSelectedItem isn't null and I reset the xSaveBtn.DataContext to that object, I am still seeing the No Item Selected tooltip as if my WPF tooltip section was overriden and its no longer binding into the datacontext ItemName Property

CodePudding user response：

You are trying to set a property to two values at the same time. It's impossible. What you are doing in XAML is equivalent to:

    xSaveCurrentBtn.Tooltip = new ToolTip() {.....};

When you setting a string value to the same property, the previous value is lost. And it is not possible to restore it if you do not save it first.

You might want to assign a value in case of a binding error:

<ToolTip Content="{Binding ItemName,
                           Mode=OneWay,
                           FallbackValue='No Item Selected'}"
         ContentStringFormat="Save {0}"/>

CodePudding user response：

you can use ContentTemplate with TextBlock, which will either use StringFormat, or TargetNullValue depending on ItemName being null:

<usercontrols:ucButton.ToolTip>
    <ToolTip Content="{Binding ItemName}">
        <ToolTip.ContentTemplate>
            <DataTemplate>
                <TextBlock Text="{Binding StringFormat='Save {0}',
                                          TargetNullValue='No Item Selected'}"/>
            </DataTemplate> 
        </ToolTip.ContentTemplate>
    </ToolTip>
</usercontrols:ucButton.ToolTip>

or if you bind Tooltip.Content differently:

<usercontrols:ucButton.ToolTip>
    <ToolTip Content="{Binding}">
        <ToolTip.ContentTemplate>
            <DataTemplate>
                <TextBlock Text="{Binding Path=ItemName,
                                          StringFormat='Save {0}',
                                          FallbackValue='No Item Selected'}"/>
            </DataTemplate> 
        </ToolTip.ContentTemplate>
    </ToolTip>
</usercontrols:ucButton.ToolTip>