I have a QListView with the ViewMode set to IconMode. I would like to achieve the following DnD behavior:
If a list view item is dragged inside the view, only the items position in the view is changed. This is the same as setting DragDropMode equal to InternalMove.
If a list item is moved out of the view, it can be copied to another external view. In this case, DragDropMode is equal to DragOnly.
How do I mix the two modes in such a way that both behaviors are supported by the view?
You might be able to do this by overriding the dropEvent of your view like this:
void MyListView::dropEvent( QDropEvent* e )
{
if( e->source() != this )
{
// something comes from the outside
// what to do? return?
return;
}
else
{
// event comes from the view itself, let's do some stuff
// for example call the base class default event
QAbstractItemView::dropEvent(e);
}
}
I guess the correct flag would be QAbstractItemView::DragDrop to do this.
Related
I have an itemRenderer which changes its graphics when it is clicked.
When the list gets scrolled again or another itemrenderer is clicked I want to restore the graphics.
But how can I notice inside an ItemRenderer that the list got scrolled?
Best regrads
Chris
You can use property change event of your list. In my case i am using same and it works perfect.
lstPost.scroller.viewport.addEventListener( PropertyChangeEvent.PROPERTY_CHANGE, propertyChangeHandler);
protected function propertyChangeHandler( event : PropertyChangeEvent ) : void
{
if ( event.property == "verticalScrollPosition" )
{
//your code goes here
}
}
I'm writing a program using Qt 4.8 that displays a table (QTableWidget) filled with filenames and file's params. First an user adds files to the list and then clicks process. The code itself updates the contents of the table with simple progress description. I want the table by default to be scrolled automatically to show the last processed file and that code is ready.
If I want to scroll it by hand the widget is being scrolled automatically as soon as something changes moving the viewport to the last element. I want to be able to override the automated scroll if I detect that it was the user who wanted to change view.
This behavior can be seen in many terminal emulator programs. When there's a new line added the view is scrolled but when user forces the terminal to see some previous lines the terminal does not try to scroll down.
How could I do that?
Solution:
I created an object which filters event processed by my QTableWidget and QScrollBar embedded inside. If I spot the event that should turn off automatic scrolling I just set a flag and stop scrolling view if that flag is set.
Everything is implemented inside tableController class. Here are parts of three crucial methods.
bool tableController::eventFilter(QObject* object, QEvent* event)
{
switch (event->type())
{
case QEvent::KeyPress:
case QEvent::KeyRelease:
case QEvent::Wheel:
case QEvent::MouseButtonDblClick:
case QEvent::MouseButtonPress:
case QEvent::MouseButtonRelease:
_autoScrollEnabled = false;
default:
break;
}
return QObject::eventFilter(object, event);
}
void tableController::changeFile(int idx)
{
[...]
if (_autoScrollEnabled)
{
QTableWidgetItem* s = _table.item(_engine.getLastProcessed(), 1);
_table.scrollToItem(s);
}
[...]
}
void tableController::tableController()
{
[...]
_autoScrollEnabled = true;
_table.installEventFilter(this);
_table.verticalTableScrollbar()->installEventFilter(this);
[...]
}
Thanks for all the help. I hope somebody will find it useful :)
Subclass QTableWidget and overload its wheelEvent. You can use the parameters of the supplied QWheelEvent object in order to determine if the user scrolled up or down.
Then use a simple boolean flag which is set (or reset) in your wheelEvent override. The method which is responsible for calling scrollToBottom() should then consider this boolean flag.
You will have to find a way to figure out when to set or reset that flag, e.g. always set it when the user scrolls up and reset it when the user scrolls down and the currently displayed area is at the bottom.
connect(_table->view()->verticalScrollBar(), &QAbstractSlider::actionTriggered, this, [this](int) {
_autoScrollEnabled = false;
});
I have a simple list and a background refresh protocol.
When the list is scrolled down, the refresh scrolls it back to the top. I want to stop this.
I have tried catching the COLLECTION_CHANGE event and
validateNow(); // try to get the component to reset to the new data
list.ensureIndexIsVisible(previousIndex); // actually, I search for the previous data id in the IList, but that's not important
This fails because the list resets itself after the change (in DataGroup.commitProperties).
I hate to use a Timer, ENTER_FRAME, or callLater(), but I cannot seem to figure out a way.
The only other alternatives I can see is sub-classing the List so it can catch the dataProviderChanged event the DataGroup in the skin is throwing.
Any ideas?
Actually MUCH better solution to this is to extend DataGroup. You need to override this.
All the solutions here create a flicker as the scrollbar gets resetted to 0 and the it's set back to the previous value. That looks wrong. This solution works without any flicker and the best of all, you just change DataGroup to FixedDataGroup in your code and it works, no other changes in code are needed ;).
Enjoy guys.
public class FixedDataGroup extends spark.components.DataGroup
{
private var _dataProviderChanged:Boolean;
private var _lastScrollPosition:Number = 0;
public function FixedDataGroup()
{
super();
}
override public function set dataProvider(value:IList):void
{
if ( this.dataProvider != null && value != this.dataProvider )
{
dataProvider.removeEventListener(CollectionEvent.COLLECTION_CHANGE, onDataProviderChanged);
}
super.dataProvider = value;
if ( value != null )
{
value.addEventListener(CollectionEvent.COLLECTION_CHANGE, onDataProviderChanged);
}
}
override protected function commitProperties():void
{
var lastScrollPosition:Number = _lastScrollPosition;
super.commitProperties();
if ( _dataProviderChanged )
{
verticalScrollPosition = lastScrollPosition;
}
}
private function onDataProviderChanged(e:CollectionEvent):void
{
_dataProviderChanged = true;
invalidateProperties();
}
override public function set verticalScrollPosition(value:Number):void
{
super.verticalScrollPosition = value;
_lastScrollPosition = value;
}
}
I ll try to explain my approach...If you are still unsure let me know and I ll give you the source code as well.
1) Create a variable to store the current scroll position of the viewport.
2) Add Event listener for Event.CHANGE and MouseEvent.MOUSE_WHEEL on the scroller and update the variable created in step 1 with the current scroll position;
3) Add a event listener on your viewport for FlexEvent.UpdateComplete and set the scroll position to the variable stored.
In a nutshell, what we are doing is to have the scroll position stored in variable every time user interacts with it and when our viewport is updated (due to dataprovider change) we just set the scroll position we have stored previously in the variable.
I have faced this problem before and solved it by using a data proxy pattern with a matcher. Write a matcher for your collection that supports your list by updating only changed objects and by updating only attributes for existing objects. The goal is to avoid creation of new objects when your data source refreshes.
When you have new data for the list (after a refresh), loop through your list of new data objects, copying attributes from these objects into the objects in the collection supporting your list. Typically you will match the objects based on id. Any objects in the new list that did not exist in the old one get added. Your scroll position will normally not change and any selections are usually kept.
Here is an example.
for each(newObject:Object in newArrayValues){
var found:Boolean = false;
for each(oldObject:Object in oldArrayValues){
if(oldObject.id == newObject.id){
found = true;
oldObject.myAttribute = newObject.myAttribute;
oldObject.myAttribute2 = newObject.myAttribute2;
}
}
if(!found){
oldArrayValues.addItem(newObject);
}
}
My solution for this problem was targeting a specific situation, but it has the advantage of being very simple so perhaps you can draw something that fits your needs from it. Since I don't know exactly what issue you're trying to solve I'll give you a description of mine:
I had a List that was progressively loading data from the server. When the user scrolled down and the next batch of items would be added to the dataprovider, the scrollposition would jump back to the start.
The solution for this was as simple as stopping the propagation of the COLLECTION_CHANGE event so that the List wouldn't catch it.
myDataProvider.addEventListener(
CollectionEvent.COLLECTION_CHANGE, preventRefresh
);
private function preventRefresh(event:CollectionEvent):void {
event.stopImmediatePropagation();
}
You have to know that this effectively prevents a redraw of the List component, hence any added items would not be shown. This was not an issue for me since the items would be added at the end of the List (outside the viewport) and when the user would scroll, the List would automatically be redrawn and the new items would be displayed. Perhaps in your situation you can force the redraw if need be.
When all items had been loaded I could then remove the event listener and return to the normal behavior of the List component.
I am attempting to create a model/view application in Qt 4.7.1. I am a very new Qt developer.
Summary of what I am attempting to do:
I have a treeview that is organized as a rectangular table of rows and columns. One column of items contains a button. By default this button is to be transparent and disabled. A given button is to become visible and enabled when the mouse is hovering over its row.
The approach I am pursuing is to
find the model index for the cell that the mouse is hovering over, and
obtain a pointer to the widget associated with the widget, and
using this pointer manipulate the visibility of the button within said widget.
I cannot get a valid pointer to the widget.
my current code looks like this:
void HistoryTreeView::mouseMoveEvent(QMouseEvent *event)
{
QAbstractItemModel *m(model());
// Only do something when a model is set.
if (m)
{
QModelIndex index = indexAt(event->pos());
if (index.isValid())
{
// if the mouse has moved to another row
if (index.row() != m_currentRow)
{
m_currentRow = index.row();
QMessageBox::information( this, "HistoryTreeView", QString("index(%1)").arg(index.row()));
QWidget * item = indexWidget(index);
Q_ASSERT(item != NULL );
}
}
else // model is invalid
{
m_currentRow = -1;
}
}
QTreeView::mouseMoveEvent(event);
}
The symptoms:
I expected the call to indexWidget() to return a valid pointer to the widget the mouse is over. Instead it unexpectedly returns a NULL pointer.
Commentary:
The variable named 'index' is acting as I expected because the QMessageBox shows the correct row value. Consequently I do not think there is anything wrong with the value I am providing to indexWidget().
This is just debug code. It is missing things like code that selects the column that holds the buttons.
OK, Here is the nature of my error as I understand it.
I had incorrectly understood that every item in a view is its own widget. I now understand that the view itself is a widget, but that individual items within the view are not widgets, per se.
Because I had misunderstood that view items were widgets I believed that could:
obtain an index from a given element in a model,
use indexWidget() to obtain a Widget * to the view item associated with the model element
and then use this pointer to manipulate the view item as though it was a widget.
indexWidget() simply returned a NULL because view items are not widgets.
I have an item renderer that checks an external source for display information. If that information changes, I want to force all item renderer instances to check it.
What's the best way for force all the item renderers in a list or grid to either commitProperties or execute some other method?
I've read that resetting the
grid.itemRenderer property will make
them all initialize.
I've also received the suggestion to
iterate recursively through all the
grid's children and call invalidateProperties
on all the UIComponents I find.
Any thoughts? Alternatives?
Remember that in Flex Lists you're dealing with virtualization and itemRenderer recycling, so generally only the currently visible itemRenderers actually exist, and are therefore the ones that actually need updating.
The following works for Spark list-based controls:
for ( var i:int=0; i< sparkList.dataGroup.numElements; i++ )
{
var element:UIComponent = sparkList.dataGroup.getElementAt( i ) as UIComponent;
if ( element )
element.invalidateProperties();
else
trace("element " + i.toString() + " wasn't there");
}
If you've got 100 items, this will update the 10 visible ones and ignore the virtual rest.
If you're working with mx DataGrid, you might want to try a variant of this- but it doesn't use DataGroup / Spark virtualization so I don't have an answer for you off the top of my head.
P.S. I'm putting the finishing touches on a completely Spark-based DataGrid, I'll post the link when I'm done.
Datagroup has getItemIndicesInView() which will give you the indicies of all item renderers that are in view. Call getElementAt with those indicies.
I also usually extend ItemRenderer and add the following which will cause the item renderer's state to refresh.
public function invalidateSkinState():void
{
super.invalidateRendererState();
}
public function updateAllRenderer():void
{
if (!list.dataGroup)
return;
if (!list.dataGroup.dataProvider)
return;
for ( var index:int=0; index< list.dataGroup.numElements; index++ )
{
var item:Object = list.dataGroup.dataProvider.getItemAt(index);
var renderer:IVisualElement = list.dataGroup.getElementAt( index ) as IVisualElement;
if ( renderer )
list.updateRenderer( renderer, index, item );
}
}
works fine for me