Develop Reference

Proper way for datepickers validaton in c#? (windows forms)

Just can't get it with datepicker validation.
I have datepicker From and datepicker To, so I want to prevent the user from doing some kung fu and seting datepicker From to be bigger than datepicker To, I've bumped across some questions but couldn't find the answer, so I've tried doing the easiest way I could think of:
Set MaxDate property for datepicker from in form_load event
private void Form1_Load(object sender, EventArgs e)
{
datepickerFrom.MaxDate = datepickerFrom.Value;
}
Then do the same for value_changed event
private void datepickerFrom_ValueChanged(object sender, EventArgs e)
{
datepickerFrom.MaxDate = datepickerFrom.Value;
}
This was easy and fine, only few lines of code, and I've only needed datepickerFrom_ValueChanged event, but recently I've tried typing date into datepicker insted of selecting it, and then all hell broke loose.
So I came to some solution for validation, instead of setting MaxDate property, I've tried this.
private void dtFrom_ValueChanged(object sender, EventArgs e)
{
DateTime from = datepickerFrom.Value;
DateTime to = datepickerTo.Value;
int year= from.Year > to.Year ? to.Year : from.Year;
int month = from.Month > to.Month ? to.Month : from.Month;
int day = from.Day > to.Day ? to.Day : from.Day;
int hour = from.Hour > to.Hour ? to.Hour : from.Hour;
int minute = from.Minute > to.Minute ? to.Minute : from.Minute;
int second = from.Second > to.Second ? to.Second : from.Second;
//setting datepicker value
datepickerFrom.Value = new DateTime(year, month, day, hour, minute, second);
}
This works fine, but feels like bit of headache, and I have to do this for datepickerTO_ValueChanged event also, sure I could make one method and call it two times, but still feels like there is a batter way for this, so any suggestions?
Thank you for your time

Solution 1:
You can handle datePickerTo close event and do something like:
private void dateTimePickerTo_CloseUp(object sender, EventArgs e)
{
DateTime fromdate = Convert.ToDateTime(dateTimePickerFrom.Value);
DateTime todate1 = Convert.ToDateTime(dateTimePickerTo.Value);
if (fromdate > todate1)
//Error
}
You can also use DateTime.Compare whcih get two date
like
int result = DateTime.Compar(dateTimePickerFrom.Value ,dateTimePickerTo.Value);
if result is 1 means From date is earlier, see this link.
Note1:
but as you said if user type in From or To textboxes then closeup event never fire so you need compare them in where you want to process
such as button click.
Note2:
As #Sinatr comment if Value is DateTime then don't need to convert it so the code would be like:
if (dateTimePickerFrom.Value >dateTimePickerTo.Value)
//Error

Your proposal would lead to a horrible interface. Suppose the following case:
From = 1 jan 2000
To = 1 feb 2000
User wants to change both values to 2010. He starts with the from value:
From = 1 jan 2010
Now he wants to change the TO value to 1 feb 2010. Alas, he can't.
Proper usage would be: add some button with which the operator can affirm he has changed all data, start checking it and update. In windows this button is usually named Apply Now or OK. Why deviate from this windows standard.
private void OnFormLoading(object sender, ...)
{
this.FromDate.MinValue = ... // use the real absolute min value you want ever to allow
this.FromDate.MaxValue = ...;
this.ToDate.MinValue = ...;
this.ToDate.MaxValue = ...;
}
Don't do any checking as long as the operator is making changes. Strat checking the input values when he indicates that he finished making changes:
private void OnButtonApplyNow_Clicked(object sender, ...)
{
bool InputOk = CheckInput();
if (!inputOk)
{
ShowIncorrectInput(); // for instance using a MessageBox
}
}

Padleft on numericupdown

I would like to use a numericupdown control on my application. I'm well aware that I could use a plain textbox instead, but I rather like the way this particular control's UI fits with what I'm doing in my application.
It also needs to have 0's at the left, per desired text output. If I'm not mistaken, this is not supported by standard numericupdown controls. It should never exceed 4 digits in length. However, if I input more, it must show favor to new keystrokes and drop left-most digits instead. The up and down arrows should increment/decrement the value per usual behavior. Even after keying in values.
It should never be allowed to run negative. It should only accept whole integers. This is easily handled by the stock functionality though.

Partly posting an answer for others who may follow. Partly looking for assurance that I'm not being an idiot.
Note that this hack depends on firing Sync() before extracting the final value. The timer will fire pretty quickly, but does not guarantee that things will happen in the correct order. It may not hurt to manually trigger Sync() immediately before extracting values.
public class UpDownWith0 : System.Windows.Forms.NumericUpDown
{
private System.Windows.Forms.Timer addzeros = new System.Windows.Forms.Timer();
public UpDownWith0()
{
this.addzeros.Interval = 500; //Set delay to allow multiple keystrokes before we start doing things
this.addzeros.Stop();
this.addzeros.Tick += new System.EventHandler(this.Sync);
}
protected override void OnTextBoxTextChanged(object source, System.EventArgs e)
{
this.addzeros.Stop(); //reset the elapsed time every time the event fires, handles multiple quick proximity changes as if they were one
this.addzeros.Start();
}
public void Sync(object sender, System.EventArgs e)
{
int val;
this.addzeros.Stop();
if (this.Text.Length > 4)
{
//I never want to allow input over 4 digits in length. Chop off leftmost values accordingly
this.Text = this.Text.Remove(0, this.Text.Length - 4);
}
int.TryParse(this.Text, out val); //could use Value = int.Parse() here if you preferred to catch the exceptions. I don't.
if (val > this.Maximum) { val = (int)this.Maximum; }
else if (val < this.Minimum) { val = (int)this.Minimum; }
this.Value = val; //Now we can update the value so that up/down buttons work right if we go back to using those instead of keying in input
this.Text = val.ToString().PadLeft(4, '0'); //IE: display will show 0014 instead of 14
this.Select(4, 0); //put cursor at end of string, otherwise it moves to the front. Typing more values after the timer fires causes them to insert at the wrong place
}
}

What prevents infinite loops among interconnected Winforms controls?

On a Form I have two controls, A and B. Each one sends an event when its value changes. The Form handles A's ValueChanged event by setting B to some value, and B's ValueChanged by setting A's value.
Do I need to do anything special to prevent an infinite loop, where the user changes A, sending a ValueChanged event which causes B to update, which now sends it ValueChanged event, causing A to update...
I know some GUI toolkits, such as Qt, have logic built into the infrastructure to prevent loops like that. (See the "Enter Your Age" example in Ch. 1 of the Blanchette & Summerfield book on Qt4.) Some older toolkits required the programmer to define and manage a flag to detect recursion. For WinForms, I haven't read a definitive statement anywhere on this.
For a concrete example, suppose A and B are NumericUpDown controls to show temperature in Fahrenheit and Celsius. When the user changes one, the other updates to show the corresponding temperature in the other system.

In my experience, the loop usually ends because the values stop actually changing. Your example falls into this case. Consider the following scenario:
User changes the Fahrenheit to 32
Events update the Celsius to 0
Events set the Fahrenheit to 32
Nothing further happens because Fahrenheit did not change
This is usually implemented in the properties by putting a check at the top of the setter to not raise the changed event when the new value is the same as the current value.

The way in which I've managed to prevent this problem when implementing custom controls, is by raising events only when the value actually does get changed, like this.
public string Text
{
get { return _text; }
set
{
if (_text != value)
{
_text = value;
OnTextChanged();
}
}
}
One could argue that not checking whether the value is actually different before firing the event is bad code.
I don't recall ever experiencing these issues with Windows Forms controls, so the ones I've been using must be doing this check correctly.

The events will not loop in the NumericUpDown example that you have provided. The ValueChanged event of the NumericUpDown will only get fired when the value changes i.e. If the value of a NumericUpDown is 5 and in code you again set it to 5, no event will be fired. This behavior of the event stops it from looping when you have two NumericUpDown controls.
Now suppose you have two NumericUpDown controls A & B.
A was changed by the user, it fires an event
On the event fired by A, you calculate and set the value of B. B detects a value change and fires an event
On the event fired by B, you calculate and set the value of A. However this value would be the same as the original value and Windows will not fire an event of ValueChanged.
So in the case of Windows Form Controls, the Framework manages it for you, if you want to achieve this for your own classes you follow a similar principle. On the setter of a value, check if the new value is different from the old value. Only if it differs fire an event.

I think you should detach B event before set B in A event. So B event never fire when you set B in A event. you should same thing for B event. You can break loop.
Sorry for my English. I hope it help you.

There isn't really any standard. As a user, you should handle controls that raise useless events, and controls that do not. Even for .NET's own controls, documentation is lacking on this aspect so you're left just trying it.
Using a flag to detect recursion is possible, but nicer IMO is to change control.Value = newvalue; to if (control.Value != newvalue) control.Value = newvalue;.
That said, if you write your own controls, please do not raise useless events, and please clearly document that fact.

To answer your question I have built a simple test with the code below.
public partial class Form1 : Form
{
Random r = new Random();
public Form1()
{
InitializeComponent();
}
private void Form1_Shown(object sender, EventArgs e)
{
// This triggers the infinite loop between the two controls
numericUpDown1.Value = 10;
}
private void numericUpDown1_ValueChanged(object sender, EventArgs e)
{
int cur = (int)numericUpDown2.Value;
int r1 = r.Next(1, 100);
while (r1 == cur)
r1 = r.Next(1, 100);
Console.WriteLine("Random in NUM1=" + r1);
numericUpDown2.Value = r1;
}
private void numericUpDown2_ValueChanged(object sender, EventArgs e)
{
int cur = (int)numericUpDown1.Value;
int r1 = r.Next(1, 100);
while (r1 == cur)
r1 = r.Next(1, 100);
Console.WriteLine("Random in NUM2=" + r1);
numericUpDown1.Value = r1;
}
}
The form has only two NumericUpDown initialized with values 1 and 2.
As you could test in Visual Studio 2013 there is nothing to prevent an infinite recursion in the case in which you really manage to generate different numbers at every ValueChanged event.
To prevent the infinite loop you could use the usual technique. Declare a global form variable
bool changing = false;
Inside both events add this code
try
{
if (changing) return;
changing = true;
.... event code ....
}
finally
{
changing = false;
}

How to create a textbox that has decimal value

I need to add a textbox in my application that starts showing with the value 0.00 just like a ATM, as you type the numbers then it keeps the two decimal point until satisfied with the value for example the sequence to end up of a value of 1023.00 would be (as I type)
0.01
0.10
1.02
10.23
102.30
1023.00
Is this possible to do in a windows forms application?. I am just not sure how to go about it.
Thank you.

In this kind of scenario I would not use a textbox, but a label or a read-only textbox. To get the user input just use the key-press event on your form (you have to enable KeyPreview on the form too) - then just remember the keys/numbers pressed and output the format you are targeting - should be a rather easy algorithm (Char.IsNumber, and String.Format might come in handy):
private int _inputNumber = 0;
private void Form_KeyPress(object sender, System.Windows.Forms.KeyPressEventArgs e)
{
if (!Char.IsNumber(e.KeyChar)) return;
_inputNumber = 10*_inputNumber + Int32.Parse(e.KeyChar.ToString());
ReformatOutput();
}
private void ReformatOutput()
{
myOutput.Text = String.Format("{0:0.00}", (double)_inputNumber / 100.0);
}
Note: Why not use a textbox - because it's internal logic with select/replace/remove/type is so overcomplicated that the cases you would have to check are just to much to handle gracefully - so instead of trying to change a cannon into a sling you should start with the sling.

.net c# text box date with mask - setup

I have a c# .net project and want an input text box for a date value. I want it to display a default value of mm/dd/yyyy and then allow users to enter valid dates.
I have tried using a masked text box but it doesn't like having the above format.
If i try and use //____ looks naff and so does 00/00/0000 and of course if you put in '0' like 03/11/2009 you get 3/11/29 because the 0's are deleted as part of the mask.
What is the best way to set up an input box like this, effectively with a mask, only allowing numbers, and validation (though at this point I am not so worried about that).
This seems so simple and isn't.

Try examining the the date in the OnChange event. Check the length of the text, adding / when appropriate.
Alternatively, see if the the DatePicker may be a better choice...

Why not try and use a plugin like the jQuery UI DatePicker?
http://docs.jquery.com/UI/Datepicker
They are lightweight, tested and saves work!

Assuming Windows Forms, the DateTimePicker is the tool for the job.
Here is an example with the MaskedTextBox, but since you say it doesn't work...
Another good try, if you're using DataBinding, if by instantiating a Binding (Binding for WPF) class and handling its Parse and Format events (these don't seem to exist in WPF, but there must be some way).
In short:
Binding b = new Binding("Text", BindingSourceInstance, "data.DateCreated");
b.Parse += new EventHandler(b_Parse);
b.Format += new EventHandler(b_Format);
private void b_Format(object sender, ConvertEventArgs e) {
if (e.DesiredType != typeof(DateTime)) return;
e.Value.ToString("dd/MM/yyyy");
// Or you may prefer some other variants:
// e.Value.ToShortDateString();
// e.Value.ToLongDateString();
// e.Value.ToString("dd/MM/yyyy", CultureInfo.CurrentCulture.DateTimeInfo.ShortDatePattern);
}
private void b_Parse(object sender, ConvertEventArgs e) {
// Choose whether you to handle perhaps bad input formats...
e.Value = DateTime.Parse(e.Value, CultureInfo.InvariantCulture); // The CultureInfo here may be whatever you choose.
}

Using masked text box for date is a headache, best to use DateTime.TryParseExact() with control validated event.
It will guarantee user input in correct format without too much coding, like in this example:
you need to use also a ToolTip to instruct the user to the correct input.
private void txtEntryDate_Validated(object sender, EventArgs e)
{
if (!string.IsNullOrEmpty(txtEntryDate.Text))
{
DateTime entryDate;
if (DateTime.TryParseExact(txtEntryDate.Text, "dd/MM/yyyy", CultureInfo.InvariantCulture, DateTimeStyles.None, out entryDate))
{
// further actions for validations
}
else
{
setTooltip(txtEntryDate, "txtEntryDate", "Invalid date format date must be formatted to dd/MM/yyyy");
txtEntryDate.Focus();
}
}
else
{
setTooltip(txtEntryDate, "txtEntryDate", "Please provide entry date in the format of dd/MM/yyyy");
txtEntryDate.Focus();
}
}
and the ToolTip class:
private void setTooltip(Control Ctrl, string CtrlCaption, string ToolTipMsg)
{
ToolTip tt1 = new ToolTip();
tt1.AutoPopDelay = 5000;
tt1.InitialDelay = 1000;
tt1.ReshowDelay = 500;
tt1.ShowAlways = false;
tt1.SetToolTip(Ctrl, CtrlCaption);
tt1.Show(ToolTipMsg, Ctrl,5000);
}