VB.NET 中的自定义日期格式问题 [英] Issue with Custom Date Format in VB.NET
问题描述
大家好！
我在 VB.NET 中遇到自定义日期格式的问题，我已经尝试使用这些代码:
但他们都没有为我工作.
首先，这是我获取每月第一天和最后一天的源代码
代码:
公共函数 FirstDayOfMonth(ByVal sourceDate As DateTime) As DateTime返回新日期时间(sourceDate.Year, sourceDate.Month, 1)结束函数公共函数 LastDayOfMonth(ByVal sourceDate As DateTime) As DateTimeDim lastDay As DateTime = New DateTime(sourceDate.Year, sourceDate.Month, 1)返回 lastDay.AddMonths(1).AddDays(-1)结束函数这是输出
3/1/2018 &2018/3/31示例:
我第一次尝试基于 Source#1
Dim startDayMonth As StringDim endDayMonth As StringstartDayMonth = startDayMonth.ToString("dd")endDayMonth = endDayMonth.ToString("dd")MsgBox(startDayMonth & " " & endDayMonth)输出:
TIMELOG.exe 中发生类型为System.InvalidCastException"的未处理异常附加信息:无法将System.String"类型的对象转换为System.IFormatProvider"类型.我第二次尝试基于 Source#2
Dim startDayMonth As DateTimeDim endDayMonth As DateTimeDim dateFormat As String日期格式 = "%d"startDayMonth = FirstDayOfMonth(现在)endDayMonth = LastDayOfMonth(现在)startDayMonth = startDayMonth.ToString(dateFormat)endDayMonth = endDayMonth.ToString(dateFormat)输出:
Microsoft.VisualBasic.dll 中发生类型为System.InvalidCastException"的未处理异常附加信息:从字符串1"到类型日期"的转换无效.自己的方法#1
Dim startDayMonth As DateTimeDim endDayMonth As DateTimeDim dateFormat As StringdateFormat = "yyyy-MM-dd"startDayMonth = Convert.ToString(FirstDayOfMonth(Now))endDayMonth = Convert.ToString(LastDayOfMonth(Now))startDayMonth = startDayMonth.ToString(dateFormat)endDayMonth = endDayMonth.ToString(dateFormat)输出
3/1/2018 3/31/2018自己的方法#2
Dim startDayMonth As DateTimeDim endDayMonth As DateTimeDim dateFormat As StringdateFormat = "%yyyy-MM-dd"startDayMonth = Convert.ToString(FirstDayOfMonth(Now))endDayMonth = Convert.ToString(LastDayOfMonth(Now))startDayMonth = startDayMonth.ToString(dateFormat)endDayMonth = endDayMonth.ToString(dateFormat)输出
Microsoft.VisualBasic.dll 中发生类型为System.InvalidCastException"的未处理异常附加信息:从字符串182018-03-01"到类型日期"的转换无效.在 VB.NET 中编码时，您应该设置 Option Strict On 始终，100% 的时间.
来源 #1
startDayMonth = startDayMonth.ToString("dd")endDayMonth = endDayMonth.ToString("dd")我收到一个编译时错误:
<块引用>BC30512 Option Strict On 不允许从String"到IFormatProvider"的隐式转换.
如果没有 Option Strict On，我会遇到运行时错误:
InvalidCastException:无法将System.String"类型的对象转换为System.IFormatProvider"类型.
编译时错误比运行时错误好得多.向客户部署编译时错误是不可能的.
来源#2
startDayMonth = startDayMonth.ToString(dateFormat)endDayMonth = endDayMonth.ToString(dateFormat)<块引用>
BC30512 Option Strict On 不允许从字符串"到日期"的隐式转换.
同样适用于自己的方法#1和自己的方法#2.
如果你有Option Strict On，你甚至不会问这个问题.
请打开它.然后你的编译器会告诉你哪里出错了.
Good day everyone!
I have a problem about custom date format in VB.NET and I already tried to use these codes:
but none of them are working for me.
First, this the source code where I get the first and last day of the month
Code:
Public Function FirstDayOfMonth(ByVal sourceDate As DateTime) As DateTime
Return New DateTime(sourceDate.Year, sourceDate.Month, 1)
End Function
Public Function LastDayOfMonth(ByVal sourceDate As DateTime) As DateTime
Dim lastDay As DateTime = New DateTime(sourceDate.Year, sourceDate.Month, 1)
Return lastDay.AddMonths(1).AddDays(-1)
End Function
This is the output
3/1/2018 & 3/31/2018
Example:
My first attempt based on Source# 1
Dim startDayMonth As String
Dim endDayMonth As String
startDayMonth = startDayMonth.ToString("dd")
endDayMonth = endDayMonth.ToString("dd")
MsgBox(startDayMonth & " " & endDayMonth)
OUTPUT:
An unhandled exception of type 'System.InvalidCastException' occurred in TIMELOG.exe
Additional information: Unable to cast object of type 'System.String' to type 'System.IFormatProvider'.
My second attempt based on Source# 2
Dim startDayMonth As DateTime
Dim endDayMonth As DateTime
Dim dateFormat As String
dateFormat = "%d"
startDayMonth = FirstDayOfMonth(Now)
endDayMonth = LastDayOfMonth(Now)
startDayMonth = startDayMonth.ToString(dateFormat)
endDayMonth = endDayMonth.ToString(dateFormat)
OUTPUT:
An unhandled exception of type 'System.InvalidCastException' occurred in Microsoft.VisualBasic.dll
Additional information: Conversion from string "1" to type 'Date' is not valid.
Own Method #1
Dim startDayMonth As DateTime
Dim endDayMonth As DateTime
Dim dateFormat As String
dateFormat = "yyyy-MM-dd"
startDayMonth = Convert.ToString(FirstDayOfMonth(Now))
endDayMonth = Convert.ToString(LastDayOfMonth(Now))
startDayMonth = startDayMonth.ToString(dateFormat)
endDayMonth = endDayMonth.ToString(dateFormat)
OUTPUT
3/1/2018 3/31/2018
Own Method #2
Dim startDayMonth As DateTime
Dim endDayMonth As DateTime
Dim dateFormat As String
dateFormat = "%yyyy-MM-dd"
startDayMonth = Convert.ToString(FirstDayOfMonth(Now))
endDayMonth = Convert.ToString(LastDayOfMonth(Now))
startDayMonth = startDayMonth.ToString(dateFormat)
endDayMonth = endDayMonth.ToString(dateFormat)
OUTPUT
An unhandled exception of type 'System.InvalidCastException' occurred in Microsoft.VisualBasic.dll
Additional information: Conversion from string "182018-03-01" to type 'Date' is not valid.
You should set Option Strict On always, 100% of the time when coding in VB.NET.
Source #1
startDayMonth = startDayMonth.ToString("dd")
endDayMonth = endDayMonth.ToString("dd")
I get a compile-time error:
BC30512 Option Strict On disallows implicit conversions from 'String' to 'IFormatProvider'.
Without Option Strict On I get a run-time error:
InvalidCastException: Unable to cast object of type 'System.String' to type 'System.IFormatProvider'.
Compile-time errors are infinitely better than run-time errors. It's impossible to deploy compile-time errors to customers.
Source #2
startDayMonth = startDayMonth.ToString(dateFormat)
endDayMonth = endDayMonth.ToString(dateFormat)
BC30512 Option Strict On disallows implicit conversions from 'String' to 'Date'.
The same applies with own method #1 and own method #2.
You would not have even asked this question had you have Option Strict On.
Please turn it on. Then your compiler can tell you where you are going wrong.
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