小编Ada*_*dam的帖子

我偶然发现了这一点,我很好奇为什么不能用is操作员辨别bool和Nullable<bool>？例;

void Main()
{
    bool theBool = false;
    Nullable<bool> theNullableBoolThatsFalse = false;
    Nullable<bool> theNullableBoolThatsNull = null;

    void WhatIsIt(object value)
    {
        if(value is bool)
            Console.WriteLine("    It's a bool!");
        if(value is Nullable<bool>)
            Console.WriteLine("    It's a Nullable<bool>!");
        if(value is null)
            Console.WriteLine("    It's a null!");
    }

    Console.WriteLine("Considering theBool:");
    WhatIsIt(theBool);
    Console.WriteLine("Considering theNullableBoolThatsFalse:");
    WhatIsIt(theNullableBoolThatsFalse);
    Console.WriteLine("Considering theNullableBoolThatsNull:");
    WhatIsIt(theNullableBoolThatsNull);
}

打电话Main()给;

Considering theBool:
    It's a bool!
    It's a Nullable<bool>!
Considering theNullableBoolThatsFalse:
    It's a bool!
    It's a Nullable<bool>!
Considering theNullableBoolThatsNull:
    It's …

[求助]请参阅下面的功能kivy DatePicker小部件的接受答案和源代码的应用.

我一直在学习Kivy,并决定将日期选择器小部件作为学习练习.

import kivy
kivy.require('1.4.0')    
from kivy.uix.gridlayout import GridLayout
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.label import Label
from kivy.uix.button import Button
from kivy.app import App

from datetime import date, timedelta

class DatePicker(BoxLayout):

    def __init__(self, **kwargs):
        super(DatePicker, self).__init__(**kwargs)
        self.date = date.today()
        self.orientation = "vertical"

        self.header = BoxLayout(orientation = 'horizontal', 
                                size_hint = (1, 0.2))
        self.body = GridLayout(cols = 7)
        self.add_widget(self.header)
        self.add_widget(self.body)

        self.populate_body()
        self.populate_header()

    def populate_header(self):
        self.header.clear_widgets()
        self.previous_month = Button(text = "<")
        self.next_month = Button(text = ">")
        self.current_month = Label(text = repr(self.date), …

在xslt 1.0中有以下更优雅的解决方案吗？据我所知,xslt 2.0内置了函数.

我在十进制小时内取一个数字,需要将其表示为HH:MM:SS.目前我有以下功能正常.

<xsl:variable name="decimal_hours" select="pre_lab_cost div pre_labour_rate"/>
<xsl:variable name="decimal_minutes" select="number(concat('0.',substring-after($decimal_hours, '.')))*60"/>
<xsl:variable name="decimal_seconds" select="number(concat('0.',substring-after($decimal_minutes, '.')))*60"/>
<xsl:value-of select="concat(format-number(floor($decimal_hours), '00'),
                                           ':',
                                           format-number(floor($decimal_minutes), '00'),
                                           ':',
                                           format-number(floor($decimal_seconds), '00')
                                           )"/>

我想将图像插入到Image字段中,最好使用一个存储过程来接受图像的路径.在黑客入侵后我想出了这个;

-- functional
DECLARE @parameters nvarchar(max) = '';
DECLARE @sql_string nvarchar(max) = 
N'UPDATE MyTable
  SET MyImageField = (SELECT BulkColumn 
                      FROM Openrowset(Bulk ''' + @PathToMyImage + ''', Single_Blob) ImageData)
  WHERE MyPrimaryKey = ' + CAST(@PrimaryKey AS NVARCHAR(max));

EXECUTE sp_executesql @sql_string,  @parameters

我这样做是因为当我尝试时;

--Not functional
INSERT INTO MyTable (MyImageField) 
VALUES ((SELECT BulkColumn 
         FROM Openrowset(Bulk @PathToMyImage, Single_Blob) ImageData));

SQL Server抛出一个错误,抱怨Bulk期望一个字符串.我宁愿不必使用sp_executesql来实现可维护性/可读性,还有更好的方法吗？