[Solved] QML and Drag and Drop

[xsacha]

Ok, I used re-parenting to animate the drag:

@
import QtQuick 1.0

Rectangle {
width: 640
height: 480
color: "#222222"
Component {
id: widgetdelegate
Item {
width: grid.cellWidth; height: grid.cellHeight
Image {
id: im
source: portrait;
anchors.centerIn: parent
width: grid.cellWidth - 10; height: grid.cellHeight - 10
smooth: true
fillMode: Image.PreserveAspectFit
Rectangle {
id: imRect
anchors.fill: parent; radius: 5
anchors.centerIn: parent
border.color: "#326487"; color: "transparent"; border.width: 6;
opacity: 0
}
}
Rectangle {
id: iWasHere
width: 20; height: 20; radius: 20
smooth: true
anchors.centerIn: parent
color: "white";
opacity: 0
}
states: [
State {
name: "inDrag"
when: index == grid.firstIndexDrag
PropertyChanges { target: iWasHere; opacity: 1 }
PropertyChanges { target: imRect; opacity: 1 }
PropertyChanges { target: im; parent: container }
PropertyChanges { target: im; width: (grid.cellWidth - 10) / 2 }
PropertyChanges { target: im; height: (grid.cellHeight - 10) / 2 }
PropertyChanges { target: im; anchors.centerIn: undefined }
PropertyChanges { target: im; x: coords.mouseX - im.width/2 }
PropertyChanges { target: im; y: coords.mouseY - im.height/2 }
}
]
transitions: [
Transition { NumberAnimation { properties: "width, height, opacity"; duration: 300; easing.type: Easing.InOutQuad } }
]
}
}

GridView {
    property int firstIndexDrag: -1

    id: grid
    x: 0; y: 0
    interactive: false

    anchors.rightMargin: 200
    anchors.bottomMargin: 100
    anchors.leftMargin: 200
    anchors.topMargin: 100
    anchors.fill: parent
    cellWidth: 80; cellHeight: 80;

    model: WidgetModel { id: widgetmodel }
    delegate: widgetdelegate
    Item {
        id: container
        anchors.fill: parent
    }
    MouseArea {
        id: coords
        anchors.fill: parent

        onReleased: {
            if (grid.firstIndexDrag != -1)
                widgetmodel.move(grid.firstIndexDrag,grid.indexAt(mouseX, mouseY),1)
            grid.firstIndexDrag = -1
        }
        onPressed: {
            grid.firstIndexDrag=grid.indexAt(mouseX, mouseY)
        }
    }
}

}@

Enjoy!

[kyleplattner]

Amazing, very well done. Thanks so much! I owe you a lot.

[xsacha]

Oh by the way, I read your previous thread and remembered you wanted to have that 'squiggle' thing when the user does an 'onPressAndHold' -- like iOS does. So, I did this too. I hope you learn from the code:

Main.qml
@
import QtQuick 1.0

Rectangle {
width: 640
height: 480
color: "#222222"
Component {
id: widgetdelegate
Item {
width: grid.cellWidth; height: grid.cellHeight
Image {
id: im
state: "inactive"
source: portrait;
anchors.centerIn: parent
width: grid.cellWidth - 10; height: grid.cellHeight - 10
smooth: true
fillMode: Image.PreserveAspectFit
SequentialAnimation on rotation {
NumberAnimation { to: 20; duration: 200 }
NumberAnimation { to: -20; duration: 400 }
NumberAnimation { to: 0; duration: 200 }
running: im.state == "squiggle"
loops: Animation.Infinite
}
Rectangle {
id: imRect
anchors.fill: parent; radius: 5
anchors.centerIn: parent
border.color: "#326487"; color: "transparent"; border.width: 6;
opacity: 0
}
states: [
State {
name: "squiggle";
when: (grid.firstIndexDrag != -1) && (grid.firstIndexDrag != index)
},
State {
name: "inactive";
when: (grid.firstIndexDrag == -1) || (grid.firstIndexDrag == index)
PropertyChanges { target: im; rotation: 0}
}
]
}
Rectangle {
id: iWasHere
width: 20; height: 20; radius: 20
smooth: true
anchors.centerIn: parent
color: "white";
opacity: 0
}
states: [
State {
name: "inDrag"
when: index == grid.firstIndexDrag
PropertyChanges { target: iWasHere; opacity: 1 }
PropertyChanges { target: imRect; opacity: 1 }
PropertyChanges { target: im; parent: container }
PropertyChanges { target: im; width: (grid.cellWidth - 10) / 2 }
PropertyChanges { target: im; height: (grid.cellHeight - 10) / 2 }
PropertyChanges { target: im; anchors.centerIn: undefined }
PropertyChanges { target: im; x: coords.mouseX - im.width/2 }
PropertyChanges { target: im; y: coords.mouseY - im.height/2 }
}
]
transitions: [
Transition { NumberAnimation { properties: "width, height, opacity"; duration: 300; easing.type: Easing.InOutQuad } }
]
}
}

GridView {
    property int firstIndexDrag: -1

    id: grid
    x: 0; y: 0
    interactive: false

    anchors.rightMargin: 200
    anchors.bottomMargin: 100
    anchors.leftMargin: 200
    anchors.topMargin: 100
    anchors.fill: parent
    cellWidth: 80; cellHeight: 80;

    model: WidgetModel { id: widgetmodel }
    delegate: widgetdelegate
    Item {
        id: container
        anchors.fill: parent
    }
    MouseArea {
        id: coords
        anchors.fill: parent
        onReleased: {
            if (grid.firstIndexDrag != -1)
                widgetmodel.move(grid.firstIndexDrag,grid.indexAt(mouseX, mouseY),1)
            grid.firstIndexDrag = -1
        }
        onPressAndHold: {
            grid.firstIndexDrag=grid.indexAt(mouseX, mouseY)
        }
    }
}

}@

This has been made in to a Wiki Entry:
http://developer.qt.nokia.com/wiki/Drag_and_Drop_within_a_GridView

[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.