wpf image source change work after focus changed - wpf

Question

I have wpf app with button, that should reflect two states - enabled/disabled.
The button have image as its content:
<Button Name="FindButton" Style="{StaticResource TextEditorToolbarButtonStyle}"
Command="FindButtonCommand"
Margin="2,0,10,0">
<Image Name="FindSvgViewbox" Style="{StaticResource TextEditorToolbarIconStylePng}"
Source="/Img/png/enabled/find.png"/>
</Button>
So in some cases button will be disabled, and those image source will changed like this:
FindSvgViewbox.Source = new BitmapImage(new Uri(disabledImagePath));
This works, but image actualy change only after i click on some other control like textboxt or other button, so there is some kind of lag or delay.
What can cause the problem?
EDIT:
Here is style for button:
<Style x:Key="TextEditorToolbarButtonStyle" TargetType="{x:Type Button}">
<Setter Property="Width" Value="30"></Setter>
<Setter Property="Height" Value="30"></Setter>
<Setter Property="BorderThickness" Value="0"></Setter>
<Setter Property="Background" Value="#F1F1F1"></Setter>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type Button}">
<Border Background="{TemplateBinding Background}" BorderThickness="0">
<ContentPresenter HorizontalAlignment="Center" VerticalAlignment="Center"/>
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
<Style.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Background" Value="#C5C5C5"/>
</Trigger>
</Style.Triggers>
</Style>
The image source changed in CanExecuteChanged handler for button:
FindButtonCommand = new RelayCommand(DoFind, o => FindCanExecute);
FindButtonCommand .CanExecuteChanged += (sender, args) =>
{
AppUtils.ChangeIconSource(FindButton, FindSvgViewbox);
};

Answer 1

If image source is only depends on enabled/disabled state of button (which is IsEnabled property), you can control image source value with pure XAML. Your TextEditorToolbarIconStylePng style should be like this:
<Style x:Key="TextEditorToolbarIconStylePng" TargetType="Image">
<Setter Property="Source" Value="/Img/png/enabled/find.png" />
<Style.Triggers>
<Trigger Property="IsEnabled" Value="False">
<Setter Property="Source" Value="/Img/png/enabled/findDisabled.png" />
</Trigger>
</Style.Triggers>
</Style>
Note that initial Source value should be assigned from style's Setter rather than from Image element directly, and of course you shouldn't edit Source value from code.
Also note that this style uses image's IsEnabled property, which is by default inherited from button's IsEnabled property (controlled by command), unless you will manually edit image's property.