I am trying to do the following in QT, but I'm unsure of how to do it, or even do it efficiently.
Any input would be greatly appreciated.
I have a QListView and an underlying model that I implemented myself.
The rows of the model include another class "CJTAGPin" which determine the data.
In the rows of the ListView I only need to display certain elements of this class, which works just fine.
In the same window, I have a QTableWidget, where i want rows of the Listview to be allowed to dropped.
But in this Widget, the name displayed in the List ist not enough,
and I would need the instances of "CJJTAGPin" accessible (when pressing a button accessing the cells where Objects were dropped and knowing which instance of CJTAGPin it is).
How can this be achieved?
I already did some research and found that subclassing QMimeData would be an option, but I'm not quite sure which Class I would need to be subclassing and how to rewrite hasFormat(), formats(), and retrieveData().
Related
I just read the Model/View documentation for Qt 4.8. I believe to understand how the Model/View (Delegates/SelectionModel) work. One thing that I'm unsure about is how to manipulate data when I have a for example a TreeView.
Imagine having a TreeView to display a list and buttons to remove elements from this list when an item/row is selected. I see two approaches here
1) In the slot of the PushButton I retrieve the SelectionModel and the ItemModel of the TreeView and call model->removeRow(index.row ...). This way the model (that i subclassed from QAbstractItemModel) manipulates the data that it is supposed to represent.
2) In the slot of the PushButton I remove the item directly from the data source, that the TreeView's model represents. Then I can link the data with the model via signals/slot, such that the model can then tell the TreeView that the underlying data has changed.
The same scenario can be imagined with adding elements. Should I add the new element to the data which signals its changed state to the ItemModel which the informs the TreeView, or should I add the new item through the ItemMode?
I haven't found any Best Practices documentation on this. The two approaches differ strongly, such I would like to know in advanced which one is preferable.
Does anybody have a suggestion which path to follow?
Thanks
1) is preferable - you should probably avoid manipulating your data source directly from the UI code - your life will be better if you go through the model. At the very least add a method to your model to do the data manipulation, and call that method from your UI code.
You will find that some of Qt's methods are protected such that they can only be called from the model itself (e.g. endInsertRows etc.)
Good day!
There are instances of classes QListView and QTreeView.
Both of the instances loads data from model (QStandardItemModel).
QTreeView displays positions (For example: Chief, Manager, Developer, etc).
Clicking on the title of position a list of employees revealed.
QListView displays only positions of staff.
Question:
How can I display a full list of names of employees in QListView not showing their positions?
Which methods I need to override?
What can you advise in this situation?
P.S. Thanks!
I don't think you are going to be able to do that with a single model.
This thread suggests using a proxy model to flatten the original one without having to maintain two instances of that data. But the implementation pointed to (KDE's KReparentingProxyModel) isn't exactly trivial.
There is some documentation on proxy models, and the QSortFilterProxyModel might be usable in your context, although I think you'll need something more specific.
You might also find the classes attached to the third response on this thread: ModelView - how to use proxies to filter this data? interesting as a starting point.
(Sorry this isn't very specific. Searching for "qt flatten tree model" will give you other ideas.)
Try to use QListWidget, is easier than QListView.
I want to use one data source (e.g. an Array) for multiple Datagrids that have different filterFunctions attached and show different columns.
First, I thought I use a very straight forward apporach:
create the Array
create an ArrayCollection for every DataGrid and set the "source" property to the Array
create the DataGrids and set their dataProvider property to its designated ArrayCollection
So now. every ArrayCollection can have its own filterFunction, sort state etc. but there needs to be only one Array with all the data in memory.
Now to the point that totally confused me:
As new items are added to the Array, of course no Events are dispatched and I have to call itemUpdated manually on each of the ArrayCollections. While debugging into the code in order to get a deeper understanding for Flex, I tried to figure out, what this misterious "itemUpdated" method does, especially as it notes in the adobe documentation, that, if no "property" is given (e.g. it is null), a simple "refresh()" will occur.
I did not find any calls to "refresh()" in the whole debugging (and I went down the framework whole as deep as possible (btw: lots of funny comments right in the code :-) )).
The only thing I could find was a CollectionChangeEvent getting dispatched with a PropertyChangeEvent in its "item" property. Which was of the kind "UPDATE" (and not, as I would expect "ADD"). When trying to dispatch that event manually, it never worked (e.g. the datagrid did not update).
I know I have to stick with itemUpdated for the moment, but as the dataprovider can get big (in both dimensions), performance does concern me and I wnat to understand what is going on under the hood.
And as expected, no help from adobe :-(
So a big thanks for everyone who read this whole text.
And an even bigger THANKS to anyone who answers and gives me the slightes hint in how I can get out of the confusion and understand (if thats possible at all) Fles a little better.
finest of all regards,
herbert
You have to call ArrayCollection.refresh() for each of your dataProviders to get the dataGrids to show the new changes to the source array.
I've a simple question regarding the update of a QTreeView (or any subclass of QAbstractItemView) when a model object changes externally. Let's say that a list shows a subclass of QAbstractItemModel, and an item of that model gets changed outside of the list window, and we would like to update the list with the change. What is the usual strategy to achieve something like this ? I've looked at the Qt documentation of QAbstractItemModel and there is a signal named 'dataChanged' that is (or should be) emited when data from the model changes. But since this signal (as all QAbstractItemModel functions/signals/slots) work with a QModelIndex, which is not persistent as the documentation clearly says, am i supposed to store somehow a mapping of my data to QPersistentModelIndex(es), so when my data change i will be able to find the corresponding QPersistenModelIndex and use that as argument to the various QAbstractItemModel functions ? Is that what QPersistentModelIndex(es) are used for ? Or am i missing something ?
Thank you.
ps: I guess i could just reload the QTreeView, but then i wouldn't know which items were expanded or which were selected. Is there an strategy to overcome this problem and just reload the list ?
QTreeView already handles the case in which the underlying model's data changed (i.e. the model has emitted the dataChanged() signal). That means you don't need to do any additional work on the view.
If you're implementing your own model (a derived class of QAbstractItemView), and you're making a change to the contents of the model, you simply need to emit the dataChanged() signal when your change is complete. The signal/slot mechanism will automatically inform the view using that signal.
I have a checkbox in a Flex DataGrid, and when I scroll, other rows are randomly checked/unchecked.
After reading over: Creating a column of RadioButtons in Adobe Flex
it's clear that the itemRenderers are getting recycled, but the problem I have with the solution presented there is it moves info about the view into the model.
Does anyone have a better way of solving it, that doesn't force me to put information for the UI into my actionscript model classes? (in my case, I am converting incoming XML data to actionscript classes, and these are getting bound to my datagrid).
Thanks for the help.
thanks everyone. great tips. unfortunately it was becoming too much overhead to keep the model pure, so i just polluted the model like the link in my original post. :( at least it works.
Chetan, neat idea.. i tried working with this for almost an entire day with no luck though.
brd6644, good thoughts on separating the two model classes.. i might go back and do this later.
You could create a subclass of DataGrid that internally stores what rows are checked/unchecked (Array/Collection of Boolean) but you would have a devil of a time keeping that in sync with the dataProvider when it is sorted or filtered. I suppose you could use a Dictionary that is keyed by the object in each index of the dataProvider and valued with a Boolean to indicate whether it's selected. That would at least isolate you from the sorting / filtering issues. This will not work if you have duplicate references in your dataProvider.
Alternatively, you could create a subclass of your ActionScript model class and add the "selected" property to it, then write some simple utility methods to "convert" between the two. That way your View deals only with the "ViewModel" class and other layers (especially the server side) deals only with the real "Model" class.
Adding to what cliff.meyers said, there is a third option of creating a custom IList class as described in this blog post by Alex Harui. It is pretty clever actually, and is cleaner as it doesn't require subclassing the component or polluting your model classes.