there's problem about Children().Clear(),whether it can be optimized

[thomasbrook]

At first, a control of type scrollview has six child control of type compose. the child control will be removed, when i click button named create.Then,i call Children().Clear(), new child control will be add to parent control.

Two child controls are not removed. Four child controls are not dispose.

package main

import (
    "fmt"

    "github.com/lxn/walk"
    . "github.com/lxn/walk/declarative"
)

func main() {
    mw := new(MyMainWindow)
    m := MainWindowInit(mw)
    if _, err := m.Run(); err != nil {
        fmt.Println(err)
    }
}

type MyMainWindow struct {
    *walk.MainWindow
    sv *walk.ScrollView
}

func MainWindowInit(mw *MyMainWindow) *MainWindow {

    m := &MainWindow{
        AssignTo:   &mw.MainWindow,
        Title:      "MainWindow",
        Background: SolidColorBrush{Color: walk.RGB(0x5F, 0x69, 0x8E)},
        Layout:     VBox{},
        Size:       Size{550, 340},
        Children: []Widget{
            PushButton{
                Text: "create",
                OnClicked: func() {
                    childlist := mw.sv.Children()
                    if childlist != nil {
                        childlist.Clear()
                        //                      for i := childlist.Len() - 1; i >= 0; i-- {
                        //                          ch := childlist.At(i)
                        //                          ch.SetParent(nil)
                        //                          ch.Dispose()
                        //                      }
                        fmt.Println("clear ok!")
                    }
                    loadChild(mw.sv)
                    return
                },
            },
            ScrollView{
                AssignTo: &mw.sv,
                Layout: Flow{
                    MarginsZero: true,
                    Alignment:   AlignHNearVNear,
                },
                Children: []Widget{
                    Composite{
                        Layout:     VBox{},
                        Background: SolidColorBrush{Color: walk.RGB(0x00, 0x8B, 0x8B)},
                        Children: []Widget{
                            Label{
                                Alignment: AlignHNearVCenter,
                                Font:      Font{PointSize: 11},
                                Text:      "hello walk ",
                                Visible:   true,
                                TextColor: walk.RGB(0xFF, 0xFF, 0xFF),
                            },
                        },
                    },
                    Composite{
                        Layout:     VBox{},
                        Background: SolidColorBrush{Color: walk.RGB(0x00, 0x8B, 0x8B)},
                        Children: []Widget{
                            Label{
                                Alignment: AlignHNearVCenter,
                                Font:      Font{PointSize: 11},
                                Text:      "I am fine. ",
                                Visible:   true,
                                TextColor: walk.RGB(0xFF, 0xFF, 0xFF),
                            },
                        },
                    },
                    Composite{
                        Layout:     VBox{},
                        Background: SolidColorBrush{Color: walk.RGB(0x00, 0x8B, 0x8B)},
                        Children: []Widget{
                            Label{
                                Alignment: AlignHNearVCenter,
                                Font:      Font{PointSize: 11},
                                Text:      "I am fine. ",
                                Visible:   true,
                                TextColor: walk.RGB(0xFF, 0xFF, 0xFF),
                            },
                        },
                    },
                    Composite{
                        Layout:     VBox{},
                        Background: SolidColorBrush{Color: walk.RGB(0x00, 0x8B, 0x8B)},
                        Children: []Widget{
                            Label{
                                Alignment: AlignHNearVCenter,
                                Font:      Font{PointSize: 11},
                                Text:      "I am fine. ",
                                Visible:   true,
                                TextColor: walk.RGB(0xFF, 0xFF, 0xFF),
                            },
                        },
                    },
                    Composite{
                        Layout:     VBox{},
                        Background: SolidColorBrush{Color: walk.RGB(0x00, 0x8B, 0x8B)},
                        Children: []Widget{
                            Label{
                                Alignment: AlignHNearVCenter,
                                Font:      Font{PointSize: 11},
                                Text:      "I am fine. ",
                                Visible:   true,
                                TextColor: walk.RGB(0xFF, 0xFF, 0xFF),
                            },
                        },
                    },
                    Composite{
                        Layout:     VBox{},
                        Background: SolidColorBrush{Color: walk.RGB(0x00, 0x8B, 0x8B)},
                        Children: []Widget{
                            Label{
                                Alignment: AlignHNearVCenter,
                                Font:      Font{PointSize: 11},
                                Text:      "I am fine. ",
                                Visible:   true,
                                TextColor: walk.RGB(0xFF, 0xFF, 0xFF),
                            },
                        },
                    },
                },
            },
        },
    }
    return m
}

func loadChild(parent walk.Container) error {
    for i := 0; i < 8; i++ {
        w := Composite{
            Layout:     VBox{},
            Background: SolidColorBrush{Color: walk.RGB(0x00, 0x8B, 0x8B)},
            Children: []Widget{
                Composite{
                    Layout: VBox{},
                    Children: []Widget{

                        Label{
                            Alignment: AlignHNearVCenter,
                            Font:      Font{PointSize: 11},
                            Text:      "smile",
                            Visible:   true,
                            TextColor: walk.RGB(0xFF, 0xFF, 0xFF),
                        },
                    },
                },
            },
        }

        err := w.Create(NewBuilder(parent))
        if err != nil {
            panic(err)
        }
    }

    return nil
}

[lxn]

You should change your OnClicked handler to something like this:

...
    OnClicked: func() {
        childlist := mw.sv.Children()
        if childlist != nil {
            mw.sv.SetSuspended(true)
            defer mw.sv.SetSuspended(false)

            for i := childlist.Len() - 1; i >= 0; i-- {
                childlist.At(i).Dispose()
            }
            fmt.Println("clear ok!")
        }
        loadChild(mw.sv)
        return
    },
...

WidgetList.Clear only removes all widgets from a container, but does not dispose of them. Calling Dispose on a widget on the other hand does both.

For best results you should always wrap operations that would trigger multiple layout updates in parent.SetSuspended(true); defer parent.SetSuspended(false).

[thomasbrook]

In this way, I did not think of a specific scenario. But,WidgetList.Clear is not remove all widgets from a container.It may be a bug. As you loop through the list in the method onClearingWidgets of the file container.go，you also remove the control from the list in the method SetParent.

I'm not sure if I'm right.

[lxn]

Clearing children should be fixed by https://github.com/lxn/walk/commit/65fec213208b35277f369146b05d233ad1de6504.

[thomasbrook]

After use parent.SetSuspended, usage experience is very fine.thanks.