C# Window Visibility, collapsed and hidden

Question

I have a quick question regarding visibility of windows in an application. According to... http://msdn.microsoft.com/en-us/library/system.windows.visibility.aspx (its short)

When a window is collapsed no space is reserved for the window in layout. When a window is hidden space is reserved for the window in layout.

I'm confused here, what is the layout referring to? Is it referring to window space?

Answer 1

Here's an illustration:

 <Grid>
        <TabControl>
            <TabItem Header="Visible"></TabItem>
            <TabItem Visibility="Hidden" Header="Hidden">Hidden</TabItem>
            <TabItem Visibility="Hidden" Header="Hidden">Hidden</TabItem>
            <TabItem Visibility="Hidden" Header="Hidden">Hidden</TabItem>
            <TabItem Header="Visible"></TabItem>
            <TabItem Header="Visible"></TabItem>
            <TabItem Header="Visible"></TabItem>
        </TabControl>
    </Grid>

Will render this:

And this XAML:

<Grid>
    <TabControl>
        <TabItem Header="Visible"></TabItem>
        <TabItem Visibility="Collapsed" Header="Collapsed">Collapsed</TabItem>
        <TabItem Visibility="Collapsed" Header="Collapsed">Collapsed</TabItem>
        <TabItem Visibility="Collapsed" Header="Collapsed">Collapsed</TabItem>
        <TabItem Header="Visible"></TabItem>
        <TabItem Header="Visible"></TabItem>
        <TabItem Header="Visible"></TabItem>
    </TabControl>
</Grid>

Will render this:

So, Collapsed will not save the space, whereas Hidden will.

Answer 2

No, its referring to the whole window you are looking at.

Lets say, you have at the top of the screen a Red Block (20px height) and below the Red Block you have a title.

Hidden: The Red Block is NOT visible, but the space it normally reserves, is still reserved, meaning the Title is is 20px away from the top of the screen

Collapsed: The Red Block is NOT visible together with the reserved space (the 20px height), meaning the Title is located at the top of the screen