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csharp Value of '01/01/0001 00:00:00' is not valid how to handle?

if (File.Exists(settingsFile))
{
string[] lines = File.ReadAllLines(settingsFile);
if (lines.Length > 0)
{
trackBarHours.Value = Convert.ToInt32(optionsfile.GetKey("trackbarhours"));
trackBarMinutes.Value = Convert.ToInt32(optionsfile.GetKey("trackbarminutes"));
trackBarSeconds.Value = Convert.ToInt32(optionsfile.GetKey("trackbarseconds"));
savedMilliseconds = Convert.ToInt32(optionsfile.GetKey("milliseconds"));
dateTimePicker1.Value = Convert.ToDateTime(optionsfile.GetKey("timetargetvalue"));
richTextBox1.Text = optionsfile.GetKey("result");
}
}
because the key "timetargetvalue" is not yet created in the settingsFile because i didn't saved it yet for the first time the value of the key of "timetargetvalue" is '01/01/0001 00:00:00'
in that case that there is no yet the key hwo can i handle the datetime exception ?
dateTimePicker1 is a DateTimePicker control.
the exception is on the line :
dateTimePicker1.Value = Convert.ToDateTime(optionsfile.GetKey("timetargetvalue"));
System.ArgumentOutOfRangeException: 'Value of '01/01/0001 00:00:00' is not valid for 'Value'. 'Value' should be between 'MinDate' and 'MaxDate'.
Parameter name: Value'
what should i check against of so it will not throw the exception ?

DateTimePicker.Value must be above DateTimePicker.MinimumDateTime, which is 'January 1, 1753'.
When you haven't set the timetargetvalue, it will resolve to '01/01/0001 00:00:00', as you have seen, which is too early.
So you need to check the value before assigning it to DateTimePicker.Value.
You can do it like this:
DateTime tempDateTime = Convert.ToDateTime(optionsfile.GetKey("timetargetvalue");
dateTimePicker1.Value = tempDateTime >= DateTimePicker.MinimumDateTime ? tempDateTime : DateTimePicker.MinimumDateTime;

When dealing with a Struct such as DateTime that does not have any value we need to consider that this is not a class and can not be set to null. It must always have some value. (see https://learn.microsoft.com/en-us/dotnet/api/system.datetime?view=net-7.0)
The exception mentions in a round about way that the range of acceptable values is between dateTimePicker1.MinDate and dateTimePicker1.MaxDate so one option is to check if your value is within this range. But it's unlikely to be the best option. (see https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.datetimepicker.mindate?view=windowsdesktop-6.0)
I'm pretty sure that DateTime default value is equal to that of DateTime.Min but if you really wanted to check if the value is default then I would suggest comparing it to default(DateTime) would be better.
This pretty much covers the use of DateTime and value defaults when null is not an option. Which brings up a possibly more desirable option. Encapsulation.
We could instead encapsulate the DateTime struct into a Nullable class. The encapsulating class will be nullable and will also be able to present the encapsulated value through a property called Value. (see https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/nullable-value-types)
There are two ways to declare such a Nullable class, both of which compile to the same thing:
Nullable<DateTime> myNullableDate = null;
DateTime? anotherNullableDate = null;
Since the DateTime is encapsulated in a Nullable object we can start using a null reference check. We can also call a method on Nullable called HasValue which returns a bool (True if it has a value).
EDIT: I notice that you're not doing any checks before trying to parse the DateTime and then directly setting it into the DateTimePicker.Value which can accept a null value. (although setting null won't clear a previously set value).
As such perhaps what you might want to do is handle the scenario a bit better and then use a DateTime.TryParse() instead. (see https://learn.microsoft.com/en-us/dotnet/api/system.datetime.tryparse?view=net-7.0)
e.g. (not the most optimized code, but I think it's easier to follow along in a more verbose form)
private DateTime? LoadDateFromOptions(string key)
{
var rawValue = optionsfile.GetKey(key);
if (!string.IsNullOrEmpty(rawValue))
{
return null;
}
DateTime dateValue;
bool isSuccess = DateTime.TryParse(rawValue, out dateValue);
if (isSuccess)
{
return dateValue;
}
else
{
return null;
}
}
and then instead of having that exception you can load the value optionally a bit more like this:
var timeTarget = LoadDateFromOptions("timetargetvalue");
if (timeTarget != null)
{
dateTimePicker1.Value = timeTarget;
}

DateTime.Now in class constructor

Good day all.
I am working on something that handles tasks.
Each task consists of 3 strings and a DateTime Object
Below is the constructor I built.
public Task(string von, string was, string an, DateTime zeit = DateTime.Now)
When compiling I get compiler error
Default parameter value for 'zeit' must be a compile-time constant (CS1736)
I assume the problem is, that -obvioulsy- the value for DateTime.Now depends on the time the constructor is called, which is the whole point that I want to have here.
I already looked at [this] thread, but it does not really apply to me, because the memory demand for a DateTime Object is always the same and that thread says the problem is the unknown heap-demand of that call.1
I already have an idea for a work-around (see below), but as we all know work-arounds are not best practice
public Task(string von, string was, string an, DateTime zeit){
if(zeit == null)
dateOfCreation = DateTime.Now; //dateOfCreation being the name of Task's internal DateTime field.
else
dateOfCretion = zeit;
So if I want to use the current DateTime I pass null. However: If I take the time and effort to always specifically pass null, I might as well each time pass DateTime.Now.
Question:
Is there a way to get parameter DateTime zeit = DateTime.Now accepted or substituted with identical outcome?

Use Constructor overloading instead:
public Task(string von, string was, string an, DateTime zeit)
{
...
}
public Task(string von, string was, string an) : this(von, was, an, DateTime.Now)
{
...
}

Resharper suggests but does not perform any refactoring to this code block

In the following method, parameters fromDate and toDate's value are never used because they are overwritten in the body before being read.
static void GetDatesFromMonth(string month, ref DateTime fromDate, ref DateTime toDate)
{
DateTime userDateTime = TimeHelper.getUserGMTNow();
DateTime calculatedDate = Convert.ToDateTime(month + " 01," + userDateTime.Year);
toDate = calculatedDate.AddMonths(1).AddSeconds(-1);
fromDate = toDate.AddMonths(-12).AddSeconds(1);
}
I am using this code at many places in my class file.
When I run Resharper on my code it shows this message and unlike all its other suggessions it is not able to correct this code block
can anybody help me to rewrite this method with good coding practice.

Change the two date parameters to out
static void GetDatesFromMonth(string month, out DateTime fromDate, out DateTime toDate)
See here for a clarification on out vs ref
Simply, you use out when your method need to return two or more values, the out means 'I will set this values before exiting'. On the contrary ref is more complicated. It means 'I need this values/objects inside this method and I will change them before exit'

Alternatively since out parameters are generally a code smell you may want to rewrite your method as something like:
static Tuple<DateTime, DateTime> GetDatesFromMonth(string month)
{
...
}
or
static ToFromDates GetDatesFromMonth(string month)
{
...
}
with
class ToFromDates
{
public DateTime To{get;set;}
public DateTime From{get;set;}
}
You could also create an extension method
static class DateExtensions
{
public static Tuple<DateTime, DateTime> GetDatesFromMonth(this string month)
{
...
}
}
and use this in your code like this
var dates = "January".GetDatesFromMonth();

Simply use out in place of ref. It will show your intentions (that parameters will be out parameters) and it will also indicate that initial values of those parameters are irrelevant. That should also fix R# warning. If you use ref, R# expects you to use the parameter values before any overwrite.

What should be the default value in a DateTime optional parameter?

Normally, if I have a nullable type for an optional parameter, I would put null as the default value. This way I know that if the value is null, the caller doesn't want to specify any value for that one.
public void Foo(string text, string text2= null);
If the parameter is normally a positive integer, I can use a negative number
public void Foo(string text, int index=-1);
How about DateTime? It is not nullable, and (as far as I know) it doesn't have a meaningless number that cannot be a true input either (like -1 for positive integer). Or is there? What would you use in this situation?
I also know that I can use the nullable DateTime type, but this means that the method caller will have to use Nullable as well as opposed to just conveniently pass a DateTime.

You can make value types nullable using the ? operator in C#:
DateTime? myDate = null;
From this, you can make the parameter optional:
void Foo(DateTime? myDate = null)
{
}
Further reading on Nullable Types.
This is not the only way to skin the cat however, you can use default(DateTime), however you cannot use DateTime.MinValue, MaxValue, or Now in optional parameters because they are not compile time constants.
Of course, you don't need to use optional parameters, you can use overloaded methods if you wish to make use of Min, Max, or Now.
void Foo()
{
Foo(DateTime.MinValue);
}
void Foo(DateTime d)
{
}
If you want to go overkill (well, maybe not overkill, plenty of valid reasons to do this), then you could define a new date type that understands when it has a value:
class SmarterDateTime
{
public bool IsSet { get; set; }
// Wrapper around DateTime etc excluded.
}
As for what should be the default, you can choose to make any date represent a default if you wish, but for things like optional parameters you'll have limitations.
Personally, I tend to use DateTime.MinValue.

default (DateTime) - operator default is intended for It

At the question "what can be a default value for a DateTime" the response must be: you can only use default(DateTime). This because the default value must be const and both DateTime.MinValue and DateTime.MaxValue are only static readonly, but note that
default(DateTime) == DateTime.MinValue
down to the Kind.
If you want you can implement an overload with one less parameter (the DateTime) and from that overload call the "main" method passing the value you prefer.
But as written by others, the problem is that you wrote wrong premises.
No, DateTime (as nearly all the ValueTypes. Nearly all because Nullable<Nullable<int>> is illegal, even while Nullable<T> is a ValueType) is nullable. Nullable<DateTime> or DateTime? (same thing)
Even int are nullable, you know? int? :-)

DateTime.MinValue will be the default value.

check the dateTime default parameter , its value would be 1/1/0001 12:00:00 AM,
private void M(Int32 x = 9, String s = “A”, DateTimedt = default(DateTime), Guidguid = new Guid()) {
Console.WriteLine(“x={0}, s={1}, dt={2}, guid={3}”, x, s, dt, guid);
}

If you use the Nullable the callers of your function can just pass a regular DateTime to it, so they won't notice a thing :) There are implicit operators that will do this for you
If you want to set a default in your function you can do:
public void Foo(DateTime? value = null)
{
if ( value == null )
{
value = ... // default
}
}

Code Snippet
public DateTime method1()
{
if (condition)
return new DateTime(2007, 5, 30, 11, 32, 00);
else
return default(DateTime);
}
The default statement will initialise a value type to it's default value. In the case of a datetime this value is also exposed as a static property called DateTime.MinValue. If using C# 1.0 the statement "default(DateTime)" would be equivalent to "DateTime.MinValue". You could use this special value as a kind of "marker" value, meaning if it is returned it indicates an invalid datetime.
If using C# 2.0 again, it is also possible to use what is called a nullable type, and actually return NULL, as shown in the following example
Code Snippet
public DateTime? method2()
{
if (condition)
return new DateTime(2007, 5, 30, 11, 32, 00);
else
return null;
}

// This is the best way to null out the DateTime.
//
DateTime dateTime2 = DateTime.MinValue;

You might consider using the value DateTime.MinValue and use overloading.

Depends on your use-case.
Any that won't match real data will work, but that depends on your use of it (so in a way does -1 for integers, since it's a perfectly good integer only for your use of it being one were only positive integers make sense).
If you are sending a minimum date (interested in all foo that are later) then any date prior to the earliest sensible date will do, and code like .Where(f -> f.When > myDate) will work without even having to look for that special case.
Likewise with maximum dates in reverse (any date that would be after the latest sensible date).
Otherwise, just avoid the use of defaults entirely, and overload instead.

Passing javascript Date object to C# WebBrowser control using window.external

I am able to call C# methods of WebBrowser.ObjectForScripting with javascript window.external from WebBrowser WinForms control and pass string, int, bool etc. However I don't know how to pass javascript Date object and somehow convert/marshal it to .NET DateTime class.
Obviously, I could pass a string and parse it, but this is really not the point. I'm just curious how could I do it with javascript Date and .NET DateTime?

You can take advantage of the fact that dates in Javascript are expressed as the number of milliseconds elapsed since the UNIX epoch (1970-01-01 00:00:00 UTC). Use the valueOf() method to obtain that value from a Date object :
var millisecondsSinceEpoch = yourDate.valueOf();
If you can marshal that value to C# as a double, you can create the appropriate DateTime object using its constructor and the AddMilliseconds() method:
DateTime yourDateTime = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc)
.AddMilliseconds(millisecondsSinceEpoch);

I finally got it working. I don't know why, but I am unable to use it with dynamic. Here is the solution:
[ComVisible(true)]
public class Foo
{
public void Bar(object o)
{
var dateTime = (DateTime)o.GetType().InvokeMember("getVarDate", BindingFlags.InvokeMethod, null, o, null);
Console.WriteLine(dateTime);
}
}

I found better solution for my project.
in javascript:
var date = new Date();
myComObject.DoSomething(date.getVarDate());
in C#
[ComVisible(true)]
public class Foo
{
public void Bar(DateTime dateTime)
{
Console.WriteLine(dateTime);
}
}