修复cron任务重复执行bug

Control/Other/BacklogNotificatin.xaml

@@ -15,7 +15,7 @@
 
         <Image Source="/Resource/Image/BacklogImg.png" Margin="22,35,22,361" />
 
-        
+
         <hc:Card MaxWidth="250" Height="200" BorderThickness="0" Effect="{DynamicResource EffectShadow2}" Margin="8">
             <!--Card 的内容部分-->
             <Border CornerRadius="4,4,0,0" Width="160" Height="160">

Control/Other/BacklogNotificatin.xaml.cs

@@ -40,13 +40,15 @@ namespace GeekDesk.Control.Other
             if (info.ExecType == TodoTaskExecType.CRON)
             {
                 CronExpression exp = new CronExpression(info.Cron);
-                DateTime dtNow = DateTime.Now;
-                DateTimeOffset ddo = DateTime.SpecifyKind(dtNow, DateTimeKind.Local);
-                string nextExecTime = ddo.LocalDateTime.ToString("yyyy-MM-dd HH:mm:ss");
-                info.ExeTime = nextExecTime;
+                DateTime nowTime = DateTime.Now;
 
-                DateTime nextTime = ddo.LocalDateTime;
-                TimeSpan ts = nextTime.Subtract(dtNow);
+                //计算下次执行时间
+                DateTime nextTime = DateTime.SpecifyKind(exp.GetNextValidTimeAfter(nowTime).Value.LocalDateTime, DateTimeKind.Local);
+
+                string nextTimeStr = nextTime.ToString("yyyy-MM-dd HH:mm:ss");
+                info.ExeTime = nextTimeStr;
+
+                TimeSpan ts = nextTime.Subtract(nowTime);
                 int minutes = (int)Math.Ceiling(ts.TotalMinutes);
                 if (minutes < 0)
                 {
@@ -62,7 +64,8 @@ namespace GeekDesk.Control.Other
                 {
                     Growl.SuccessGlobal("下次任务将在 " + minutes + " 分钟后提醒您!");
                 }
-            } else
+            }
+            else
             {
                 appData.ToDoList.Remove(info); //执行任务删除
                 appData.HiToDoList.Add(info);  //添加历史任务
@@ -120,7 +123,7 @@ namespace GeekDesk.Control.Other
             ToDoInfo info = this.DataContext as ToDoInfo;
             int time = int.Parse(DelayTime.Text);
             string type = DelayType.Text;
-            switch(type)
+            switch (type)
             {
                 case "分":
                     info.ExeTime = DateTime.Now.AddMinutes(time).ToString("yyyy-MM-dd HH:mm:ss");