Bug: Unable to call QML methods with parameters

[Andrew Jackman]

I don't see this getting any love on the GitHub page, so I'd like to post it here: https://github.com/go-qml/qml/issues/90

Please refer to the following URL as the pertinent QML reference: http://qt-project.org/doc/qt-5/qml-qtqml-models-listmodel.html

My intent is to manipulate a QML TableView. The data model for the TableView is a ListModel. When attempting to do a simple fetch of a model row, I get a panic. Here is the relevant code:

The Go file:

package main
import (
        "fmt"
        "gopkg.in/qml.v1"
        "log"
        "math/rand"
        "os"
        "time"
)
var engine *qml.Engine
func main() {
        if err := qml.Run(run); err != nil {
                fmt.Fprintf(os.Stderr, "error: %v\n", err)
                os.Exit(1)
        }
}
func run() error {
        engine = qml.NewEngine()
        component, err := engine.LoadFile("bug.qml")
        if err != nil {
                return err
        }
        ctrl := Control{}
        context := engine.Context()
        context.SetVar("ctrl", &ctrl)
        window := component.CreateWindow(nil)
        ctrl.Root = window.Root()
        rand.Seed(time.Now().Unix())
        window.Show()
        window.Wait()
        return nil
}
type Control struct {
        Root qml.Object
}
func (ctrl *Control) Debug(obj qml.Object) {
        log.Println(obj.Int("count"))
        x := 1
        log.Println(obj.Call("get", x))
}

The QML file:

import QtQuick 2.0
import QtQuick.Controls 1.2
import QtQml.Models 2.1
Rectangle {
    id: root
    width: 640
    height: 480
    gradient: Gradient {
        GradientStop { position: 0.0; color: "#3a2c32"; }
        GradientStop { position: 0.8; color: "#875864"; }
        GradientStop { position: 1.0; color: "#9b616c"; }
    }
    TableView {
        id: tableROList
        TableViewColumn{ role: "title"  ; title: "Title" ; width: 100 }
        TableViewColumn{ role: "author" ; title: "Author" ; width: 200 }
        model: modelROList
        width: root.width
    }
    ListModel {
        id: modelROList
        ListElement{ title: "A Masterpiece" ; author: "Gabriel" }
        ListElement{ title: "Brilliance"    ; author: "Jens" }
        ListElement{ title: "Outstanding"   ; author: "Frederik" }
    }
    Rectangle{
        width:20
        height: 20
        color:"blue"
        x: 620
        y: 460
        MouseArea {
            id: mouseArea
            anchors.fill: parent
            drag.target: parent
            onReleased: ctrl.debug(modelROList)
        }
    }
}

Output:

jackman@debian:~/code/qmlbug$ cd ~/code/qmlbug/ && go run ./src/main.go
OpenGL Warning: Failed to connect to host. Make sure 3D acceleration is enabled for this VM.
2014/08/25 12:33:04 3
panic: invalid parameters to method "get"
goroutine 16 [running]:
runtime.panic(0x55c360, 0xc2080004b0)
        /home/jackman/code/go/src/pkg/runtime/panic.c:279 +0xf5
gopkg.in/qml%2ev1.cmust(0x7f7e50728160)
        /home/jackman/code/gopath/src/gopkg.in/qml.v1/qml.go:808 +0x90
gopkg.in/qml%2ev1.(*Common).Call(0xc2080003b0, 0x5a7210, 0x3, 0xc208000460, 0x1, 0x1, 0x0, 0x0)
        /home/jackman/code/gopath/src/gopkg.in/qml.v1/qml.go:663 +0x1d5
main.(*Control).Debug(0xc2080002c0, 0x7f7e61c9b490, 0xc2080003b0)
        /home/jackman/code/qmlbug/src/main.go:52 +0x163
reflect.Value.call(0x5806e0, 0xc2080002c0, 0x0, 0x138, 0x5a2d10, 0x4, 0xc20803a140, 0x1, 0xa, 0x0, ...)
        /home/jackman/code/go/src/pkg/reflect/value.go:563 +0x1210
reflect.Value.Call(0x5806e0, 0xc2080002c0, 0x0, 0x138, 0xc20803a140, 0x1, 0xa, 0x0, 0x0, 0x0)
        /home/jackman/code/go/src/pkg/reflect/value.go:411 +0xd7
gopkg.in/qml%2ev1.hookGoValueCallMethod(0x7f7e5016b980, 0xc208004180, 0x7fff00000000, 0x7fffb94068f0)
        /home/jackman/code/gopath/src/gopkg.in/qml.v1/bridge.go:507 +0x4a8
gopkg.in/qml%2ev1._Cfunc_applicationExec(0x589680)
        gopkg.in/qml.v1/_obj/_cgo_defun.c:60 +0x31
gopkg.in/qml%2ev1.Run(0x5df9c0, 0x0, 0x0)
        /home/jackman/code/gopath/src/gopkg.in/qml.v1/bridge.go:61 +0x1ac
main.main()
        /home/jackman/code/qmlbug/src/main.go:15 +0x2f
goroutine 19 [finalizer wait]:
runtime.park(0x4a5bb0, 0x87e398, 0x86e789)
        /home/jackman/code/go/src/pkg/runtime/proc.c:1369 +0x89
runtime.parkunlock(0x87e398, 0x86e789)
        /home/jackman/code/go/src/pkg/runtime/proc.c:1385 +0x3b
runfinq()
        /home/jackman/code/go/src/pkg/runtime/mgc0.c:2644 +0xcf
runtime.goexit()
        /home/jackman/code/go/src/pkg/runtime/proc.c:1445
goroutine 17 [syscall]:
runtime.goexit()
        /home/jackman/code/go/src/pkg/runtime/proc.c:1445
goroutine 20 [semacquire]:
sync.runtime_Semacquire(0xc2080003a4)
        /home/jackman/code/go/src/pkg/runtime/sema.goc:199 +0x30
sync.(*Mutex).Lock(0xc2080003a0)
        /home/jackman/code/go/src/pkg/sync/mutex.go:66 +0xd6
gopkg.in/qml%2ev1.(*Window).Wait(0xc208000370)
        /home/jackman/code/gopath/src/gopkg.in/qml.v1/qml.go:868 +0x9b
main.run(0x0, 0x0)
        /home/jackman/code/qmlbug/src/main.go:40 +0x1ec
gopkg.in/qml%2ev1.func·002()
        /home/jackman/code/gopath/src/gopkg.in/qml.v1/bridge.go:58 +0x46
created by gopkg.in/qml%2ev1.Run
        /home/jackman/code/gopath/src/gopkg.in/qml.v1/bridge.go:60 +0x1a5
exit status 2
jackman@debian:~/code/qmlbug$

I am using QML 5.3.1 as the TableView is not available in 5.0.3 (the recommended version on GitHub).

I tried looking for a model use of the Call() method in the repository with parameters, but I just didn't find one.

I ran the same code against Qt 5.1.1, and I get the same result.

I also tried explicitly declaring the type of 'x' as an int, int16, int32, and int64. With the exception of int16 (not yet implemented), the output among all of these was similar.

[Gustavo Niemeyer]

Sorry for not providing a more timely response to your ticket, Andrew.

I'll have to spend some time looking at why the default Qt
introspection capabilities are failing with that function, but my
guess is that it is related to how there's some JavaScript-specific
magic in its definition.

Meanwhile, there's an easy way to workaround the issue: define a
function like this in your modelROList type:

function myget(i) { return modelROList.get(i) }

and call that from Go instead. This will be a standard function, and
won't suffer from these anomalies.

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--

gustavo @ http://niemeyer.net

[Andrew Jackman]

Thanks!

-----
A. R. Jackman
801-432-0541
jac...@moonman.biz

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