The progress bar is a simple control that an application can use to visually indicate the progress of a lengthy operation. By default, the progress bar window is filled from left to right, as the operation progresses. The control has a range and a current position. The SimpleProgressBar in Microsoft Expression Blend only supports a horizontally orientated progress bar.
Breaking down the control template
The SimpleProgressBar control template consists of the following items:
A Grid layout panel, which is used to hold the multiple child objects within the progress bar. The Grid is also used because it makes it easier for an application user interface (UI) designer to add more objects to the template.
A Border element named PART_Track, which is used to represent the bar area to be filled.
A Border element named PART_Indicator, which is used to represent the bar area that has already been filled.
Do not rename any object whose name begins with "PART_" because these objects are referred to from the code that implements the control.
Property triggers used
The SimpleProgressBar control template does not use triggers. All control behavior is implemented in code.
The following brush resources in the SimpleStyles.xaml resource dictionary are used by the SimpleProgressBar template:
The Background property of the PART_Track object is set by using the PressedBrush.
The BorderBrush property of the PART_Track object is set by using the SolidBorderBrush.
The Background property of the PART_Indicator object is set by using the MouseOverBrush.
The BorderBrush property of the PART_Indicator object is set by using the NormalBorderBrush.
Best practices and design guidelines
In general, use a Grid control as the root of your template if you expect a designer to add further visual elements to your control. Expression Blend looks for a layout panel like the Grid control and makes it active by default so that new objects that are added to the artboard end up as child objects of the layout panel.
If you want, you can add triggers to the SimpleProgressBar template, or modify the PART_Indicator object to make the bar look more interesting, but do not rename any object whose name begins with "PART_" because these objects are referred to from the code that implements the control.