gtk logic behind treeviewcolumns needing cell renderers

Question

From what I understand about GTK, if I have a TreeView, I can't just use any widget I want to display information about a column. For text, you need a gtk.CellRendererText. For toggle buttons, a gtk.CellRendererToggle. For anything else, it seems you have to implement yourself, which, from a sample one for buttons that I saw, doesn't look straightforward.

Firstly, is this the case? Is there an easy way to set up whatever widget you want to be used to display some text? If not, then why is it implemented this way? If I were designing GTK i would just create some sort of system where when a row was added and when some data model information changes, user-specified callbacks would be called which would add the appropriate widget or change it, respectively.

Answer 1

To write a custom CellRenderer (copy-pasted from this link!):

• Register some new properties that your renderer needs with the type system and write your own set_property and get_property functions to set and get your new renderer's properties.

• Write your own cell_renderer_get_size function and override the parent object's function (usually the parent is of type GtkCellRenderer. Note that you should honour the standard properties for padding and cell alignment of the parent object here.

• Write your own cell_renderer_render function and override the parent object's function. This function does the actual rendering.

And there is a good/simple example for pyGTK.

Writing a custom CellRenderer is not too hard, the hardness is that how to write a custom widget. If you have learned how to write a custom widget, then writing a custom CellRenderer is easy.

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The logic behind this design is flexibility. A TreeViewColumn indicates how the data (from a TreeModel) should be displayed by a CellRenderer, thus a TreeViewColumn which represents a value of boolean type, can be displayed as a text (CellRendererText) or can be displayed as a check box (CellRendererToggle). e.g. a TreeViewColumn which represents a value of integer type, can be displayed as a text (CellRendererText) or can be displayed as a progress bar (CellRendererProgress) or can be displayed as a spin button (CellRendererSpin) or can be displayed as everything that we want.