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29 lines
2.6 KiB
Plaintext
29 lines
2.6 KiB
Plaintext
chapter.of: Widgets
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created: 20140717174605570
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modified: 20140717181806148
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sub.num: 2
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tags: doc
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title: Selective Update
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With [[Messages]] a widget is able to put some kind of events into the TiddlyWiki application which is one part of the dynamic behaviour of widgets.
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The other part is selective updating.
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Widgets are often dependant on tiddler states.
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The [[ListWidget|http://tiddlywiki.com/#ListWidget]] for example can be configured to list all tiddlers which are tagged with "important".
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Now, when such a tiddler is changed and it's "important" tag is removed, this change should reflect in the ~ListWidget.
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To allow widgets to react on such changes, each widget can provide a function ``refresh(changedTiddlers)``.
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The [[RootWidget|RootWidget and Rendering Startup]] is registered to the wiki store, using the [[Event Mechanism]]. When an change event occurs it starts to call the refresh function of its children with a list of the changed tiddlers.
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Each widget can then decide if it has to change or re-render its DOM representation and call the refresh function of its own children.
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This way every time a tiddler or the wiki store itself changes, each widget can instantly react on these changes or ignore them.
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Another way of updating are text reference attributes (text references explained in [[Transclusion and TextReference]]):
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```js
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{type: "indirect", textReference: <textReference>}
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```
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When a widget got a attribute which is a text reference and the refresh function is called, it can check if the text reference references a changed tiddler and update accordingly.
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Nearly every state of the UI is stored in tiddlers. A search mechanism for example would use a ~EditTextWidget which shows an text input field for the search string and a ListWidget to show the results.
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The ~EditTextWidget is bound to a tiddler [[$:/temp/search]]. Meaning when editing the text in the input field the tiddlers content is changed to this text. On the other hand when the tiddler changes the [[RootWidget|RootWidget and Rendering Startup]] is notified. It then starts calling its childrens refresh methods. Eventually the refresh method of the ~EditTextWidget is called and it can re-render itself if necessary.
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This way TiddlyWiki can re-use an already existing data structure which is not only convenient because we don't need to introduce an additional structure but tiddlers managed in the wiki store are already a pretty powerful data structure, supporting an [[Event Mechanism]] (so we don't need an additional observer pattern), [[Caching]], Metadata by additional tiddler fields and a [[way to obtain specific tiddlers|Tags and Filter Mechanism]].
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