How to design the collapsed view of my custom ActivityDesigner

The built-in designers of activities like Sequence can be collapsed to a more compact view. In my custom activity designer, the collapse button is there (at right top) but apparently nothing happens if I click it. I want it to collapse to just showing the title bar (like the 开发者_开发问答Delay activity). Is this possible?

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There is a sample in the MSDN

And another one.