Add clean close example

.gitignore

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+*.exe

examples/build.bat

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+@echo off
+:: cd every subdirectory and run command go build
+for /d %%i in (*) do (
+    :: skip img dir
+    if "%%i"=="img" goto :skip
+    set lastdir=%%i
+    cd %%i || goto error
+    echo Building %%i
+    go build || goto error
+    cd ..    
+)
+
+exit /b 0
+
+:error
+echo Error building %lastdir%: %errorlevel%
+exit /b %errorlevel%

examples/close/close.exe.manifest

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+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0">
+	<assemblyIdentity version="1.0.0.0" processorArchitecture="*" name="SomeFunkyNameHere" type="win32"/>
+	<dependency>
+		<dependentAssembly>
+			<assemblyIdentity type="win32" name="Microsoft.Windows.Common-Controls" version="6.0.0.0" processorArchitecture="*" publicKeyToken="6595b64144ccf1df" language="*"/>
+		</dependentAssembly>
+	</dependency>
+	<application xmlns="urn:schemas-microsoft-com:asm.v3">
+		<windowsSettings>
+			<dpiAwareness xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">PerMonitorV2, PerMonitor</dpiAwareness>
+			<dpiAware xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings">True</dpiAware>
+		</windowsSettings>
+	</application>
+</assembly>

examples/close/close.go

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+// Copyright 2013 The Walk Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"time"
+
+	"github.com/tailscale/walk"
+
+	. "github.com/tailscale/walk/declarative"
+)
+
+func main() {
+	err := run()
+	if err != nil {
+		fmt.Println("Error:", err)
+		os.Exit(1)
+	}
+	fmt.Println("Exited cleanly")
+	os.Exit(0)
+}
+
+func run() error {
+	var mw *walk.MainWindow
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	if err := (MainWindow{
+		AssignTo: &mw,
+		Title:    "Window Closing Test",
+		Layout:   VBox{Spacing: 2},
+		Size:     Size{800, 600},
+	}.Create()); err != nil {
+		walk.MsgBox(nil, "Error", fmt.Sprintf("%v", err), walk.MsgBoxIconError)
+		return fmt.Errorf("creating main window: %w", err)
+	}
+
+	mw.Closing().Attach(func(canceled *bool, reason walk.CloseReason) {
+		//walk.MsgBox(nil, "Info", fmt.Sprintf("Closing now (reason %d)", reason), walk.MsgBoxIconInformation)
+		//check if context is done
+		if ctx.Err() != nil {
+			return
+		}
+		*canceled = true
+		fmt.Println("Got close message")
+		mw.SetTitle("Closing...")
+		cancel()
+	})
+
+	go func() {
+		<-ctx.Done()
+		fmt.Println("Doing clean up process...")
+		time.Sleep(1 * time.Second)
+		mw.Close()
+		walk.App().Exit(0)
+	}()
+	code := mw.Run()
+	if code != 0 {
+		return fmt.Errorf("main window closed with %d", code)
+	}
+	return nil
+}