[Solved] QML and Drag and Drop

Deqing

Hi Sacha,

The demo of drag and drop code looks cool!

I tried the code(Main2.qml) of second version in the wiki but failed with following error: "ReferenceError: Can't find variable: gridId"

Is there anything I can do to avoid this?

THanks

xsacha

Well, I didn't write the second version.
I tested my (first) version and provided a video of that exact code running.

I can review the second one for you to discover the issue. It seems a lot better than my version so I hope you can get it working.

baysmith

I'm responsible for the second version. I tried to update this post with a "I’ve updated the above wiki entry with an alternate implementation." like I did on the "other thread":http://developer.qt.nokia.com/forums/viewreply/14354/, but it failed for some reason.

As it turns out, the second version requires Qt 4.7.1. It gives that error with Qt 4.7.0. Thanks for pointing it out. I wasn't aware of this difference in the versions. I've updated the wiki page with a notation about this.

xsacha

By the way, I just fixed in a critical issue with the first version in the wiki. It was to do with the moving code.
Problem was discovered and fixed in this thread: http://developer.qt.nokia.com/forums/viewthread/2460/P15/

The issue was that if you dragged items forward, the call to 'move' would push the indices backwards (to -1, -2 and so on) and you would no longer be able to drag the '-1' index and other items would become out of whack.

It is most noticeable on a 3-item grid.

I think the issue is only if you don't have animation onMove. The second example uses such an animation so it should be fine. Just be careful if you disable the animation.

Deqing

Thank you guys. I finally get the second version working.

It turns out that "gridId" should be defined in WidgetModel.qml, and it must starts with 0. For example:

@
ListElement { icon: "images/widget1.png"; gridId: 0 }
ListElement { icon: "images/widget2.png"; gridId: 1 }
ListElement { icon: "images/widget3.png"; gridId: 2 }
@

kyleplattner

Still returning:

@file:///Users/kp/Desktop/Precision Work/Screen Design/FinalScreens/QMLFinal/Rearrange4.qml:22: TypeError: Result of expression 'grid.items' [undefined] is not an object.@

xsacha

I have made a cleaner version of the 'second version'
Halved the lines of code, removed quite a lot of redundancy and doesn't require Qt4.7.1.
Personally, I think the grids list is a bit silly when it can be done with the model/delegate. So I have completely removed the IconItem and grids.
No loss of functionality.
I replaced the first version with it. You can check it out in the wiki.

baysmith

The grids list was made because when I added behaviors in the delegate, it wasn't working. I don't know why it wasn't working for me, but what you've got is working. I'll remove the second version now that it is obsolete.

xsacha

Yeah, I know, you can't animate a GridList.
I discussed this "in another thread.":http://developer.qt.nokia.com/forums/viewthread/2327/#13163

Basically, you need to reparent the items within the delegate. Then you have complete freedom of movement and animation. I reparented the images to the MouseArea.

Deqing

Looks like in the new code the grid can't be resized, it always be 3*3.

For example if I drag the size of its parent to a long list, it should be automatically rearranged to a 1*9 grid, as the GridView will do.

xsacha

When you drag the window?
Oh I had removed that as I was running it on a mobile device. I'll add that back in, thanks.

Deqing

Just get it works by simply set width and height of GridView equal to its parent. :)

xsacha

Yeah it already does that.
Anchor is fill to parent and parent width is whatever the host operating system gives it. 640x480 is just for reference.
Try it out now?
I think the qmlviewer on Windows won't allow you to resize the window smaller than 640x480 by the way. Might need a custom qmlviewer for that.

Deqing

As I can see, the size of qmlViewer will be the same as the top item in the qml file when it starts.

Now I'm thinking of storing position of these icons.

I guess the position should be stored in the model(or somewhere else?). How to show icons in GridView according to the values stored in the model?

xsacha

Well you actually cannot change the positions of items inside a GridView.

What I have done is created items within the GridView and then reparented them to a MouseArea (outside of GridView) so that I can move them freely.
Then I assign the x,y values of the GridView locations.

If you were to create entirely new locations and not use a GridView at all, you may as well use a Flow element.

If you're just using GridView/ListView for the model/delegate, then I will answer your question:

In your model, create an 'x' and 'y' property. For example 'myx', 'myy'. Then in the image, just set:
@x=myx; y=my@

Deqing

Basically I will have a serialized icons provided by C++ code via a model, and showed out as a Gridview.

These icons then can be rearranged by user, and when user reopen the program they should be seeing the same order as they set last time.

I'm really new to QML and not sure which is the best way, Flow or GridView?

Deqing

Had tried setting x,y in model for image to display, but looks like it is not working.

I guess the reason is in this case Grid index is not matching correct image, say a 2*3 grid:

ID of GridView
0 1 2
3 4 5

Images displayed in self-defined position
4 5 1
0 2 3

When clicking at the top-left item, we'd like to pick image 4, but grid.at(index) will return 0 for us.

xsacha

Oh, I see what you mean.

Well the code I have in the wiki does exactly this.

All you need to do is save the model in to either:

QML file (overwrite the existing one on the fly)
QSettings file (do the model positions inside QSettings object).

The gridIDs are irrelevant. You can use gridId=843423 if you want. It's just a reference point.
The only thing that matters is the order of the ListElements inside the ListModel.

However, in saying this, if you keep the gridIDs as is and save the final gridIDs in to a QSettings object (uses less space/quicker to load), then you can simply use 'move' commands at runtime to sort them in to the correct order. It's another option.

Since you said you are loading the model via a C++ backend, it only makes sense to load the model in the order you want. This solves your problem.

Deqing

Thanks. I will try it in my C++ code.

Another concern is about flickable. Sometimes user would like to flick the page when they have a lot of icons that displayed out of the screen. GridView have this feature by setting 'interactive' to true. However if we reparent items out of the GridView, these items will lost this feature.

Actually I tried to comment out reparenting code, IconItem.qml like this:
@
Component {
// Rectangle {
// id: main
// width: grid.cellWidth; height: grid.cellHeight
// opacity: 0.5
Image {
id: item//; parent: loc
width: grid.cellWidth; height: grid.cellHeight
@

In this code icon can be rearranged inside the GridView somehow, but grid failed to find correct index underneath cursor(don't know why)

Is it possible to add flickable back to the GridView?

xsacha

I only set interactive to false because it makes it easier to demo and you won't accidently flick the grid. It was unnecessary with only a 3x3 grid.

If you want to set interactive to true, just remember to use contentX and/or (depending on flickable direction) contentY to get the position within the flickable (GridView) item.

Example:
@y: main.y - grid.contentY + 5@

Note: You'll also have to make sure the grid doesn't flick while you are moving an icon.
@interactive: loc.currentId == -1@

With these two lines, it is working perfect with flickable here.

Edit: You may get some extraordinary lagg and weird effects with flickable. You need to modify Behavior on x and y, with this:
@ enabled: loc.currentId != -1 && item.state != "active"@