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| − | Storing view state is done in two commons ways, depending
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| − | on whether you want to store settings between
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| − | workbench sessions or across invocations of your view. The first of these
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| − | facilities is found directly on <tt>IViewPart</tt>. When the workbench
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| − | is shut down, the method <tt>saveState</tt> is called on all open views.
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| − | The parameter to this method is an <tt>IMemento</tt>, a simple
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| − | data structure that stores hierarchies of nodes containing numbers
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| − | and strings. Here is an example from the recipe application in the FAQ
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| − | examples, where a view is persisting the current selection of a list viewer
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| − | in a memento:
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| − | <pre>
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| − | private static final String STORE_SELECTION =
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| − | "ShoppingList.SELECTION";
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| − | public void saveState(IMemento memento) {
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| − | super.saveState(memento);
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| − | ISelection sel = viewer.getSelection();
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| − | IStructuredSelection ss = (IStructuredSelection) sel;
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| − | StringBuffer buf = new StringBuffer();
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| − | for (Iterator it = ss.iterator(); it.hasNext();) {
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| − | buf.append(it.next());
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| − | buf.append(',');
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| − | }
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| − | memento.putString(STORE_SELECTION, buf.toString());
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| − | }
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| − | </pre>
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| − |
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| − | When the workbench is reopened, the method
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| − | <tt>init(IViewSite, IMemento)</tt> is called the first time each view
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| − | becomes visible. The <tt>IMemento</tt> will contain all the information
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| − | that was added to it when the workbench was shut down. Note that
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| − | <tt>init</tt> is called before the <tt>createPartControl</tt> method,
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| − | so you will not be able to restore widget state directly from the
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| − | <tt>init</tt> method. You can store the <tt>IMemento</tt> instance in a field
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| − | and restore state later on when your widgets have been created. Continuing
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| − | this example, here is the code for restoring the viewer selection
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| − | when the view is reopened:
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| − | <pre>
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| − | private IMemento memento;
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| − | ...
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| − | public void init(IViewSite site, IMemento memento)
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| − | throws PartInitException {
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| − | super.init(site, memento);
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| − | this.memento = memento;
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| − | }
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| − | public void createPartControl(Composite parent) {
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| − | //create widgets ...
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| − | if (memento == null) return;
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| − | String value = memento.getString(STORE_SELECTION);
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| − | if (value == null) return;
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| − | IStructuredSelection ss = new StructuredSelection(
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| − | value.split(","));
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| − | viewer.setSelection(ss);
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| − | }
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| − | </pre>
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| − | Note that the <tt>IMemento</tt> instance can be <tt>null</tt> if the view state
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| − | was not saved from a previous session: for example, when the view
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| − | is first created.
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| − |
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| − |
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| − | Another mechanism for persisting view state is the JFace
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| − | <tt>IDialogSettings</tt> facility. The advantage of dialog settings
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| − | over the view <tt>save</tt>/<tt>init</tt> mechanism is that you can control when
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| − | settings are persisted. The <tt>saveState</tt> method is called only
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| − | if your view is open when the workbench shuts down, so
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| − | it is not useful for storing view state when the view is closed by
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| − | the user. Dialog settings, on the other hand, can be changed
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| − | and persisted whenever you want.
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| − |
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| − |
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| − | Views commonly use a combination of both dialog settings and
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| − | a memento for persisting view state. Important settings, such as
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| − | filters, sorters, and other view preferences, will be stored as
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| − | dialog settings; more transient attributes, such as selection
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| − | and expansion state, will be stored in the memento only when
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| − | the workbench is being shut down.
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| − |
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| − |
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| − | == See Also: ==
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| − |
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| − | [[FAQ_How_do_I_save_settings_for_a_dialog_or_a_wizard%3F]]
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| − |
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| − | <hr><font size=-2>This FAQ was originally published in [http://www.eclipsefaq.org Official Eclipse 3.0 FAQs]. Copyright 2004, Pearson Education, Inc. All rights reserved. This text is made available here under the terms of the [http://www.eclipse.org/legal/epl-v10.html Eclipse Public License v1.0].</font>
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