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Gaphor capabilities |
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~~~~~~~~~~~~~~~~~~~ |
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One nice feature of user interfaces is the ability to disable options that |
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don't do anything useful in a specific context. For example: it's useles to |
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enable a 'undo' button when there's no information to undo. |
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To solve this two possible solutions can be provided: |
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1. special listeners are installed to intercept state changes and act |
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2. declarative: a (limited) set of 'capabilities' is provided. Each command |
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supports one or more capabilities. |
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Standard capabilities: |
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All UML metamodel classes can act as capability. Commands can only be |
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useful for a limited set of data elements (for example for Namespace like |
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elements). These capabilities can be assigned by giving the name of the |
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elements(s) that can be affected using a command as a string ('Namespace'). |
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This option is most useful for popup menus. |
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Main window capabilities: |
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Some actions are quite useless to do, like saving a model, while there is |
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no model. |
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For a start we will distinguish the following caps.: |
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- 'element': there are model elements defined in the main element factory. |
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Diagram window capabilities: |
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- 'focus': there is an item selected in a diagram and it has the focus. |
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- 'select': one ot more items in the diagram are selected. |
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- 'undo': there is undo information present in the diagram. |
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- 'redo': there is redo information present in the diagram. |
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DiagramItems can not be used as capability. The reason is that the UML |
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model has a stable design, while the implementation of diagrams and diagram |
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items is likely to change much often. |
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Implementation |
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~~~~~~~~~~~~~~ |
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All windows are inherited from AbstractWindow. This class has a set_capability() |
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method. this method can be used to activate and deactivate capabilities. If |
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capabilities are (de)activated, all commands within a specific context (such |
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as 'main' or 'diagram') are verified. If their capabilities are not met, the |
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command in made insensitive (grayed out). Capabilities are desctibed as simple |
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text strings, such as 'undo' and 'snap_to_grid'. The capabilities themselves are |
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set by signal handlers which are attached during the window's construction. |
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