Saturday 31 May 2014

WPF Layout Controls/Containers, Layout Process, Properties and Tips

WPF Layout Controls/Containers, Layout Process, Properties and Tips

All the WPF Layout containers are panels that derive from the abstract System.Windows.Controls.Panel class. Mainly, there are five layout containers in WPF:

1. StackPanel
2. WrapPanel
3. DockPanel
4. Grid
5. Canvas

I am not going to explain working of all these panels as it is already very well explained here. I will add some extra details about these layout controls in WPF. I will go through WPF Layout Process Stages (Measure Stage and Arrange Stage), how can we create our custom layout containers using MeasureOverride() and ArrangeOverride() methods, different WPF layout properties and some tip and noteworthy points about WPF layout containers.

WPF Layout Process

WPF Layout takes place in two stages:

A) Measure Stage: The container loops through its child elements and asks them to provide their preferred size.
B) Arrange Stage: The container places the child elements in the appropriate position.

Creating WPF Custom Layout Containers

The Panel class also has a bit of internal plumbing you can use if you want to create your own layout containers. Most notably, you can override the MeasureOverride() and ArrangeOverride() methods inherited from FrameworkElement to change the way the panels handle measure stage and arrange stage when organizing its child elements.

WPF Layout Properties

1. Layout Properties of Layout Containers are HorizontalAlignment, VerticalAlignment, Margin, Width, Height, MinWidth, MinHeight, MaxWidth and MaxHeight

2. Default HorizontalAlignment for a Button is Stretch and for a Label is Left.

3. You can set margin for each side of a control in the order left, top, right and bottom. For example:

<Button Margin="1,2,3,4">OK</Button>

In this case, Left Margin = 1, Top Margin = 2, Right Margin = 3 and Bottom Margin = 4.

4. DesiredSize Property: You can find out the size that button wants by examining  the DesiredSize property, which returns the minimum width or the content width, whichever is greater.

5. ActualWidth and ActualHeight Properties: You can find out the actual size used to render an element by reading the ActualHeight and ActualWidth properties. But those values may change when window is resized or the content inside it changes.

6. SizeToContent Property: You can create automatically sized window in WPF if you are creating a simple window with dynamic content. To enable automatic window sizing, remove the Height and Width properties of Window and set the Window.SizeToContent property to WidhtAndHeight. The window will make itselft just large enough to accommodate all its contents. You can also allow a window to resize itself in just one dimension by using the SizeToContent value of Width or Height.

7. Border CornerRadius Property: CornerRadius property allows you to gracefully round the corners of your border. The greater the corner radius, the more dramatic the rounding effect is.

8. WPF Elements should not be explicitly sized.

9. There are three values for visiblity enumeration for elements:

A) Visible: Element is visible
B) Hidden: Element is invisible but the space occupied by it is still reserved.
C) Collapsed: Element is invisible and it also does not take up any space.

WPF Layout Containers - Tips and Noteworthy Points

1. Default orientation of StackPanel is Vertical while default orientation of WrapPanel is Horizontal.

2. DockPanel LastChildFill Property: LastChildFill when set to true, tells the DockPanel to give the remaining space to the last element.

3. DockPanel, Grid and Canvas uses Attached Properties. DockPanel has one attached property: DockPanel.Dock. Grid has two attached properties: Grid.Row and Grid.Column. Canvas has four attached properties: Canvas.Top, Canvas.Left, Canvas.Right and Canvas.Bottom.

4. Grid ShowGridLines Property: ShowGridLines property when set to true, shows all the border of cell and rows.

5. If you don't specify Grid.Row property to the child elements, those child elements are placed on row number 0. Same is the case with Grid.Column.

6. The Grid supports three sizing categories:

A) Absolute Sizes: <ColumnDefination Width="100"></ColumnDefination>
B) Automatic Sizes: <ColumnDefination Width="Auto"></ColumnDefination>
C) Proportional Sizes: <ColumnDefination Width="*"></ColumnDefination>

You can also add weight to proportional sizes: 

<ColumnDefination Width="*"></ColumnDefination>
<ColumnDefination Width="2*"></ColumnDefination>

It means, the second column is twice as bigger as the first one.

7. You can also span rows and columns in a grid.

<Button Grid.Row="0" Grid.Column="0" Grid.RowSpan="2">RowSpannedButton</Button> 

<Button Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="2">RowSpannedButton</Button>

8. You can add GridSplitter to a Grid to give the user ability to resize rows and columns.

9. You can also create uniform grids in WPF. Uniform Grids don't require any row and column definition. Example:

<UniformGrid Rows="2" Columns="2">
<Button>Top Left</Button>
<Button>Top Right</Button>
<Button>Bottom Left</Button>
<Button>Bottom Right</Button>

10. All the layout containers can be nested.

11. Canvas is the most lightweight layout container. 

12. Canvas allows you to place elements by using exact coordinates which is a poor choice of designing rich data-driven form.

13. Canvas.ClipToBounds property is used to clip the contents which fall outside the canvas.

14. Canvas.ZIndex property is used when there are overlapping elements in Canvas. The child element having greater ZIndex value will be shown above other child elements.

15. InkCanvas is used to allow stylus input. InkCanvas lets the user annotate contents with strokes.

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