添加统计日期选择功能

InfoChemicalStatistics.xaml

@@ -4,8 +4,19 @@
              x:Class="SunlightAggregationTerminal.InfoChemicalStatistics"
              Title="耗用统计">
     <Grid>
-        <Grid>
-            <CollectionView x:Name="CardCollectionView">
+        <Grid RowDefinitions="Auto, *" >
+            <Grid ColumnDefinitions="*, Auto" Grid.Row="0" Grid.Column="0" Margin="5">                
+                <HorizontalStackLayout Grid.Row="0" Grid.Column="0" Margin="5,0,0,0" >
+                    <DatePicker x:Name="StartTime" Format="yyyy年MM月dd日" FontSize="16" 
+                    MaximumWidthRequest="150" MinimumWidthRequest="130" WidthRequest="135"/>
+                    <Label Text="~" FontSize="28"/>
+                    <DatePicker x:Name="EndTime" Format="yyyy年MM月dd日" FontSize="16"
+                    MaximumWidthRequest="150" MinimumWidthRequest="130" WidthRequest="135"/>
+                </HorizontalStackLayout>
+                <Button Grid.Row="0" Grid.Column="1" Text="查询" Clicked="Button_Clicked"           
+                        WidthRequest="60" Padding="5,0,5,0" Margin="20,0,0,5" />
+            </Grid>
+            <CollectionView Grid.Row="1" x:Name="CardCollectionView">
                 <!-- 保持滚动条 -->
                 <CollectionView.ItemTemplate>
                     <DataTemplate>