优化 查找界面 机台号，工序号，可以输入 “空”

WSDDBBrower/WSDDBBrower/PgSelect.xaml

@@ -11,7 +11,7 @@
       d:DesignHeight="450" d:DesignWidth="800"
       Title="PageSelect">
     <Page.Resources>
-
+        <local:IntNullValueConverter x:Key="intNullConv"/>
     </Page.Resources>
     <Grid>
         <Grid.RowDefinitions>
@@ -45,11 +45,11 @@
                             <StackPanel Orientation="Horizontal">
                                 <StackPanel Orientation="Vertical" Margin="{StaticResource ControlMargin}">
                                     <TextBlock Style="{StaticResource TitleStyle}" Text="机台号"/>
-                                    <TextBox Style="{StaticResource ValueStyle}" Text="{Binding MachineNo}"/>
+                                    <TextBox Style="{StaticResource ValueStyle}" Text="{Binding MachineNo, Converter={StaticResource intNullConv}}"/>
                                 </StackPanel>
                                 <StackPanel Orientation="Vertical" Margin="{StaticResource ControlMargin}">
                                     <TextBlock Style="{StaticResource TitleStyle}" Text="工序号"/>
-                                    <TextBox Style="{StaticResource ValueStyle}" Text="{Binding StepNo}"/>
+                                    <TextBox Style="{StaticResource ValueStyle}" Text="{Binding StepNo, Converter={StaticResource intNullConv}}"/>
                                 </StackPanel>
                                 <controls:ToggleSwitch Header="只查找超出标准工艺"
                                        Margin="{StaticResource ControlMargin}"

WSDDBBrower/WSDDBBrower/PgSelect.xaml.cs

@@ -293,5 +293,37 @@ namespace WSDDBBrowser
         }
     }
 
+    public class IntNullValueConverter : IValueConverter
+    {
+        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
+        {
+            if (value == null)
+                return "";
+            else if (value is int)
+            {
+                return value.ToString();
+            }
+            else
+                return null;
+        }
 
+        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
+        {
+            if (value is string) 
+            {
+                if (string.IsNullOrEmpty((string)value))
+                {
+                    return null;
+                }
+                else if (int.TryParse((string)value, out int v))
+                {
+                    return v;
+                }
+                else {
+                    return null;
+                }
+            }
+            return null;
+        }
+    }
 }