[Solved] QML and Drag and Drop

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"@

Deqing

Gosh! It works perfectly.
Thank you Sacha.

Deqing

Hi Sacha, just found an issue about reparenting item. If beginResetModel()/endResetModel() called, icons will failed to be erased when moving.

Sometimes icons could be updated with new data, so I need to reset model to refresh icons. New images can be displayed out but they can't be erased anymore.

Any ideas how to fix this? Thanks in advance!

xsacha

Yeah, if you re-parent the icons, any action on the gridView won't affect them any more (even destroying the grid view!).
So what you need to do is:

Re-parent back to gridView
beginResetModel()/endResetModel() or other actions
Re-parent back to loc/screen

You can think of this as two states. Its parent should be 'loc' (or screen) when it is in a moving state because you want animations. Its parent should be the gridView when it is in a modification state (reseting model/destroying gridView or whatever else you need to do).

Deqing

Cool! I solved it by simply moving "parent: loc" into the state "active".

Thanks a lot!

kyleplattner

Just a followup question: How can I persist the drag and dropped location so that when the user navigates away from the page and returns the arrangement that the user chose is still present.

Deqing

I guess you need to store the locations in the model.

kyleplattner

I do need to keep the locations of the dragged items. What would be the best way to accomplish this?

Deqing

I'm using C++ data model and store items in a list.

When drag-and-drop finishes, I will not only move items in the GridView, but also move them inside the list in C++ code at the same time.

sfjam

this can work in one screen,but when i scroll the screen,this does not work,how to change it

xsacha

Hi sfjam. Can you elaborate on your issue?

Are you scrolling to a second GridView or scrolling within the GridView?

My solution for scrolling within a GridView is on the previous page (fourth comment from bottom).

If you want multiple GridViews, the code gets more complex. Post back if this is what you desire (multi-grid draggable icon layout).