Re: [go-qml] access qml.Context/qml.Object from outside the main func?

[Gustavo Niemeyer]

That panic message just means something is hitting a non-initialized address expecting the value to be there, which can happen for many reasons.

Regarding running things "outside of run", that's totally fine, as long as the logic is running while the run function is executing.

Can you provide a small and self-contained example that shows the problem happening?  If you don't find out the problem origin while preparing it, I'm happy to have a look.

On Sat Jan 03 2015 at 9:05:13 PM Djahma <dja...@googlemail.com> wrote:

I'm trying to populate my main GUI with qml objects received via various communication channels: os.StdIn or RPC service. But to achieve that task, I would need to access a qml.Object or Context from outside the main func/qml.Run(func(){}) in the go program.
My attempts so far always end up in a panic :run time panic:  runtime error: invalid memory address or nil pointer dereference.

Here below is a tangible example of what I'm trying to acheive. This is a program called mainUI that's being called by another called skeleton. The two communicate via RPC, and they both serve various procedures to whoever wants to connect to them. Here, "mainUI" offers the function AddMenuItem which expect a path to a qml file in order to create an object from it (that's the goal). But everytime I try to access a qml object or context from outside the "run" function, the program panics with the message quoted above.

So, why are qml types (object, engine, context) dereferenced outside of the "run" function? and is there a way to access them anyway?

package main

import (
    "fmt"
    "gopkg.in/qml.v1"
    "log"
    "os"
    "path/filepath"
    "skeleton/API/skeleton"
    "skeleton/plugin"
)

var (
    plug  *plugin.Plugin
    skel  *skeleton.Skeleton
    ctxt *qml.Context
)

func main() {
    defer func() {
        if x := recover(); x != nil {
            fmt.Println(skel.LogPrefix(), "run time panic: ", x)
        }
    }()
    //    Initialise Skeleton connection
    skel = &skeleton.Skeleton{PluginName: "mainUI"}
    if err := skel.InitRPC(); err != nil {
        fmt.Println(skel.LogPrefix(), err)
        return
    }
    //    Initialise mainUI RPC through the plugin object
    plug = &plugin.Plugin{}
    mui := new(MainUI)
    plug.Init(skel, Parse, mui)
    defer func() {
        skel.Close()
        plug.Stop()
    }()
    qml.Run(run)
}

func run() error {
    pwd, _ := filepath.Abs(filepath.Dir(os.Args[0]))
    qmlDir := pwd + string(os.PathSeparator) + "qml"
    fmt.Println(skel.LogPrefix(), "qmlDir="+qmlDir)
    engine := qml.NewEngine()
    defer engine.Destroy()
    ctxt = engine.Context()
    defer ctxt.Destroy()

    component, err := engine.LoadFile(qmlDir + string(os.PathSeparator) + "skeletonApp.qml")
    if err != nil {
        skel.Quit()
        panic(err)
    }
    window := component.CreateWindow(nil)
    defer window.Destroy()

    window.On("closing", func() { skel.Quit() })
    window.Show()
    window.Wait()
    return nil
}

type MainUI int

type MenuArgs struct {
    MenuPath []string
    ObjPath  string
}

func (m *MainUI) AddMenuItem(args *MenuArgs, err *string) error {
    defer func() {
        if x := recover(); x != nil {
            fmt.Println(skel.LogPrefix(), "run time panic: ", x)
        }
    }()
    ob :=ctxt.ObjectByName("rootApp")
    ob.Set("title", "Any Title would please me")
    return nil
}

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