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| <title>Undo Example</title> |
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| |
| <h2> |
| <b>Example - Undo</b></h2> |
| |
| <h3>Introduction</h3> |
| <p> |
| The Undo Example adds two views to the workbench. The <b>Box View</b> is a rudimentary |
| view that allows the user to create boxes by clicking into empty space and dragging the mouse |
| to form a box. Boxes can be moved by selecting a box and dragging it around. The user |
| may undo and redo any operations performed in the box view. The <b>Undo History |
| View</b> shows the undo history maintained by the workbench operations history. |
| </p> |
| <h3>Features demonstrated in the example</h3> |
| <ul> |
| <li>Creating an <tt>IUndoableOperation</tt> inside an action (Delete all boxes) to perform the action's |
| work .</li> |
| <li>Creating an <tt>IUndoableOperation</tt> based on an operation implied by a gesture (Adding |
| and moving boxes).</li> |
| <li>Using a local <tt>IUndoContext</tt> to keep undo operations local to a particular view.</li> |
| <li>Using the platform undo and redo action handlers to provide undo and redo in a view.</li> |
| <li>Providing a user preference for setting the undo limit for a particular undo context.</li> |
| <li>Using an <tt>IOperationApprover</tt> to install additional policy (Prompt before undo) in |
| the operation history.</li> |
| <li>Using <tt>IOperationHistory</tt> protocol to show undo history for different |
| undo contexts (Undo History View).</li> |
| </ul> |
| <h3>Features not demonstrated</h3> |
| <ul> |
| <li>Since the example is focused on simple undo, the BoxView code is kept |
| to a minimum. Therefore, it does not provide the expected graphical editor features such as |
| selection, resize and selection handles, color and line style attributes, etc. For the same |
| reason, advanced features in the undo framework are not shown.</li> |
| <li>There is no example of assigning multiple undo contexts in order to share operations between |
| views or editors.</li> |
| <li>There is no example of using composite undo operations.</li> |
| </ul> |
| <h3>Running the example</h3> |
| <p> |
| From Eclipse's <strong>Window</strong> menu select <strong>Show View</strong> > <strong>Other...</strong>. |
| In the <strong>Show View</strong> dialog, expand <strong>Undo Examples</strong> and select |
| the view named <strong>Box View</strong>. The box view will appear. |
| </p> |
| <p> |
| Likewise, from the <strong>Window</strong> menu select <strong>Show View</strong> > <strong>Other...</strong>. |
| In the <strong>Show View</strong> dialog, expand <strong>Undo Examples</strong> and select |
| the view named <strong>Undo History View</strong>. A view containing the undo history will appear. |
| This view can be used alongside the Box View to watch the undo history as boxes are added or moved. It |
| can also be used independently of the Box View to follow the undo history for any view or editor that |
| uses the workbench operations history to track undoable operations. |
| </p> |
| <h3>Details</h3> |
| <h4>Box View</h4> |
| <p>Click in the box view and drag the mouse to create a box that follows the mouse. Clicking inside an |
| existing box and dragging the mouse will move the box to a new location. Note the operations that appear |
| in the <strong>Undo</strong> and <strong>Redo</strong> menus as boxes are added and moved. The box view |
| can be cleared by selecting <strong>Delete all boxes</strong> from the context menu or the view's local |
| menu and toolbar. This operation can also be undone. |
| </p> |
| <h4>Undo History View</h4> |
| <p>The Undo History View shows the operations available for undo in all undo contexts. To view the history |
| in a particular undo context, select <strong>Filter on...</strong> from the view's context menu. |
| This will filter the undo history on a particular undo context. The view can be used to view the undo history |
| for the Box View, for SDK text editors, and for undoable operations that affect the workspace, such as |
| refactoring operations. Undo and redo can be performed from the Undo History View's menus. <b>Undo selected</b> |
| will attempt to undo the selected operation in the undo history, regardless of its position in the operation history. |
| Depending on the operation in question, this may or may not be allowed. For example, the Box View allows all add and |
| move operations to be undone or redone even if they aren't the most recently performed operation. Text editors |
| will prompt if an attempt is made to undo a typing operation that is not the most recent. |
| </p> |
| <h4>Example Preferences</h4> |
| <p>Preferences are provided that affect the operation of both views. |
| From Eclipse's <strong>Window</strong> menu select <strong>Preferences</strong> > <strong>Undo Preferences</strong>. |
| <ul> |
| <li><strong>Undo history limit</strong> controls how many undoable operations are kept in the history for the Box View.</li> |
| <li><strong>Show debug labels in undo history view</strong> controls whether the simple label shown in the undo menu is |
| used for displaying operations, or a debug label that includes information such as the assigned undo context(s).</li> |
| <li><strong>Confirm all undo operations</strong> controls whether prompting occurs before undoing or redoing an operation. |
| This preference is used by the operation approver installed by the example.</li> |
| </ul> |
| </p> |
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