Summary
This short article has demonstrated the usage that is basic of watchers. Ideally, at this point you learn how to make use of the tree viewer and realize where in fact the tree audience fits in the bigger JFace framework.
There are certain subjects prepared for an “advanced†tree audience article, including drag and fall, automobile increase nodes inside the tree, in-place editing and making usage of domain item properties.
Faq’s
Listed here is a listing of usually expected questions regarding utilising the tree audience.
Just how do I include or remove a product through the tree?
Addition and elimination of things is actually the exact same.
To eliminate a product through the tree audience the domain should be removed by you item from your own model. Then ask the tree audience to recharge the moms and dad regarding the domain model. Once the up-date technique is known as from the tree viewer, it’s going to ask its content provider when it comes to young kids of this moms and dad associated with the domain model. Nevertheless, as you eliminated it through the moms and dad, it won’t be here and later will undoubtedly be taken out of the view.
The content provider can be notified and perform the steps above if your domain objects trigger events, you will add the content provider as a listener so that whenever removals occur in your domain object.
How about the tree audience’s eliminate methods? If you browse the Javadoc of these practices, they’re going to tell you the eliminate techniques must certanly be called by the content provider. This will make feeling in the end, considering that the content provider accounts for providing this content. The content provider, the item would likely reappear the next time the parent of the item is refreshed if you removed the item from the tree viewer without “going through.
How do I programmatically choose a product into the tree?
Phone the tree viewer’s structuredSelection that is setSelection( new ), real).
What’s the distinction between the tree viewer’s change and refresh practices?
How can I expose a newly added model object that is concealed?
Let’s assume you’ve added the domain item book to your going package. The box that is moving currently when you look at the tree it isn’t expanded whenever you add the book to it. You would like the guide become revealed whenever you add it towards the moving field. You’ll repeat this:
My tree audience hangs or perhaps isn’t really responsive because I’m hitting a database in my own content provider. Exactly what can I Really Do?
In many UI frameworks, the audience are known as by the application’s speed dating in southern South Dakota UI thread. SWT is not any exclusion. What this means is you need to be careful to go back from listener or provider techniques in a timely fashion. In the event that you don’t, the GUI will not get events, helping to make for a sluggish and possibly useless UI.
When you yourself have an extended operating operation in your listener or provider practices, you should think about forking another thread to complete the specific work. As an example, if you should be populating your tree from a database, you can’t have your content provider looking forward to the database to go back the domain things. Rather you can have this content provider return a stub item that presents something such as “Loading Data…†although the back ground thread lots the real data.
When the history thread has loaded the info, it might need certainly to recharge the moms and dad for the stub item so your moms and dad would request its domain things once more. Now as soon as the parent requests the domain things, they currently occur since they’ve been packed through the database.
How can we include a viewer filter to a tree audience?
How can the order is changed by me associated with products in a tree audience?
Just what does the setUseHashlookup() technique do?
The setUseHashlookup(boolean) technique notifies the tree audience so it should keep a hash mapping of one’s domain item into the matching SWT TreeItem. Whenever the tree viewer has to manipulate the SWT tree products, it makes use of the hash lookup or executes a search that is recursive at the basis shopping for the product.
The tree audience manipulates SWT tree things if you include, remove, collapse, expand, unveil, refresh or upgrade a domain object. Put simply, the tree audience is manipulating tree things on a regular basis.
You need to probably always setUseHashlookup to true. The sole disadvantage to doing this is that the tree audience will need more memory because it’s keeping the mapping, however it should perform even faster with a big group of domain things.
Another essential point about tree people – generally speaking, they don’t manage domain things that map into the value that is same. Simply because the tree audience utilizes the equals() technique and possibly the hashCode() technique if you utilize the setUseHashlookup technique.