Fix settings window lifecycle

settings.go

@@ -25,6 +25,12 @@ var styleOptions = []struct {
 }
 
 func (a *App) showSettings() {
+	if a.settingsDialog != nil {
+		a.settingsDialog.Show()
+		_ = a.settingsDialog.Activate()
+		return
+	}
+
 	var dlg *walk.Dialog
 	var apiEdit, intervalEdit, cacheEdit *walk.LineEdit
 	var autoCheck, startupCheck *walk.CheckBox
@@ -39,7 +45,7 @@ func (a *App) showSettings() {
 		}
 	}
 
-	_, err := Dialog{
+	err := Dialog{
 		AssignTo: &dlg,
 		Title:    "GoWallpaper 设置",
 		MinSize:  Size{520, 300},
@@ -93,15 +99,29 @@ func (a *App) showSettings() {
 							return
 						}
 						dlg.Accept()
+						if cfg.APIURL == "" {
+							a.notifyInfo("配置已保存。刷新壁纸前需要先设置随机图片 API 地址。")
+						} else {
+							a.notifyInfo("配置已保存。")
+						}
 					}},
 					PushButton{Text: "取消", OnClicked: func() { dlg.Cancel() }},
 				},
 			},
 		},
-	}.Run(a.mw)
+	}.Create(nil)
 	if err != nil {
 		a.notifyError("无法打开设置窗口：" + err.Error())
+		return
 	}
+	a.settingsDialog = dlg
+	dlg.Closing().Attach(func(_ *bool, _ walk.CloseReason) {
+		if a.settingsDialog == dlg {
+			a.settingsDialog = nil
+		}
+	})
+	dlg.Show()
+	_ = dlg.Activate()
 }
 
 func parsePositiveInt(value, field string) (int, error) {