Develop Reference

Why don't delays work when I'm attempting to flash an error message?

Problem: I'm working on a calculator as my first MVVM application and have come across an interesting problem that I would like to understand better. My noob problem is that I'm trying to flash an error message for an invalid input--in this case I don't want the user to use the negate operator in an invalid location. In order to flash the message across the screen, I'm saving the display in another variable, setting the display to say "Invalid Operation", then I'd like to delay for half a second and reset the display to what it was before (from the temp variable). My problem is that the display variable gets set but the actual display doesn't update to show the error message, no matter how long the delay is.
I've tried both blocking (Thread.Sleep) and non-blocking delays (Task.Delay) within the function, writing separate functions to set and reset the display, and delaying within the Negate function instead, but none of these attempts allow the display to update. The display works as expected when adding and deleting characters in other parts of the code, so I don't think there's an issue with that.
Is this some sort of piping issue (the delay function actually starts before it can call the Display property) or something else entirely? I've checked other posts on here and those solutions don't seem to solve my issue. I'd love feedback on why this doesn't work as I'd expect it to as well as more efficient/effective ways to code this. Here are the relevant code blocks:
public void Negate()
{
if (Display.Length > 0)
{
if (Display[Display.Length - 1].Equals('-'))
{
Display = Display.Substring(0, Display.Length - 1);
}
else if (Display[Display.Length - 1].Equals(' ') || Display[Display.Length - 1].Equals('(') ||
Display[Display.Length - 1].Equals('E') || Display[Display.Length - 1].Equals('^'))
{
Display += '-';
}
else
{
InvalidOperation();
}
}
else
{
Display = "-";
}
}
public void InvalidOperation()
{
tempDisplay = Display;
Display = "Invalid Operation";
Thread.Sleep(500);
Display = tempDisplay;
}
public string Display
{
get
{
return _display;
}
set
{
_display = value;
OnPropertyChanged();
}
}

UI will be updated only after method InvalidOperation execution is complete, so because in last line of the method you set value back to original - there are no updates in UI.
Asynchronous approach should work, because await operator will "pause" InvalidOperation method and return execution to the message loop which will update UI controls.
public async Task InvalidOperation()
{
tempDisplay = Display;
Display = "Invalid Operation";
await Task.Delay(2000);
Display = tempDisplay;
}

Removing items from listBox over time - C#;

I'm currently working on a chatting program and the idea is to make it a secret one (Kind of like Facebook has the secret chat function).
My messages are sent to a listBox component and I want that every 10 or 'n' seconds the oldest message would get deleted. I
was trying to mark every message with an index but didn't quite understand how that works.
What I'm asking if maybe you guys know a function or could help me write one that does just that. I'm using Visual Studio 2015 Windows Forms, C#.

Well, when you have a ListBox, the items are all indexed since it's an object collection (an array of objects). Starting from 0 and going upwards for newer entries.
So let's say we add 3 items to our ListBox
listBox1.Items.Add("Item 1"); //Index 0
listBox1.Items.Add("Item 2"); //Index 1
listBox1.Items.Add("Item 3"); //Index 2
All you would have to do, is create a thread that runs in the background that deletes the item at index 0 (the oldest entry) each time.
new Thread(() =>
{
while(true)
{
if(listBox1.Items.Count > 0) //Can't remove any items if we don't have any.
{
Invoke(new MethodInvoker(() => listBox1.Items.RemoveAt(0))); //Remove item at index 0.
//Needs invoking since we're accessing 'listBox1' from a separate thread.
}
Thread.Sleep(10000); //Wait 10 seconds.
}
}).Start(); //Spawn our thread that runs in the background.

In C# WinForms a ListBox contains ListBoxItems which are a ObjectCollection (msdn-link)
So you can add any Object you like, the message which will be displayed comes from the DisplayMember
So for example
public class MyMessage {
public DateTime Received { get; set; }
public string Message { get; set; }
public string DisplayString
{
get { return this.ToString(); }
}
public string ToString() {
return "[" + Received.ToShortTimeString() + "] " + Message;
}
}
can be added as ListBoxItem.
Setting the DisplayMember to "DisplayString" (more here) will get you the correct output.
now you can iterate through the ListBoxItems, cast them as MyMessage and check the time when they were received.

I don't know if you thought about this but here's a way you could achieve this task.
First create an List of strings
List<string> list1 = new List<string>();
To use the List feature you will have to include collections in the form
using System.Collections;
Now comes the tricky part.
First declare a static integer variable globally i.e. outside all classes.
static int a;
Whenever you receive a message(considering your messages will be in string format) you've to add that string to list1 which you created.
list1.Add("the received message");
Now you've to declare a Timer (If you're new, check out how timers work). Windows forms already has timers, using that will be preferable.
The timer sends a Tick event after the desired time.
private void timer1_Tick(object sender, EventArgs e)
{
a = list1.Count() - 1; //Count will return the number of items in the list, you subtract 1 because the indexes start from 0
list1.RemoveAt(a);
listBox.Items.Clear();
foreach(string x in list1)
{
listBox.Items.Add(x);
}
}
What this code will do is, at every Tick event of the timer it will refresh the listbox, remove the last element from the array, and refill the listbox with the rest.
To use the timer just drag and drop it on the form. It's all GUI based and easy to figure out.
Let me know if you've doubts.
Tip: Make maximum use of try{} & catch{} blocks to avoid app crashes.

How to constantly delay the execution of a method

I have a ICollectionVIew named 'CompanyView'.
I also have a Filter for it called 'CompanyFilter'.
And a Textbox bound to a 'SearchCompanyTitle' property.
As I type in a databound textbox, 'CompanyFilter' gets fired with every letter and the 'CompanyView' gets filtered to show relevant results.
That works fine.
Unfortunately the table I'm filtering has about 9 000 rows so there tends to be a notable delay between the moment you press the key on the keyboard and it showing up on screen.
So what I decided to do instead was ensure that the filter was automatically fired when the user had finished typing. Which raises the question of how does the ViewModel know when the user has finished?
What I did is the below;
// This is the property the Textbox is bound to
private string _searchCompanyTitle = "";
public string SearchCompanyTitle
{
get { return _searchCompanyTitle; }
set
{
_searchCompanyTitle = value;
OnPropertyChanged("SearchCompanyTitle");
// After a character has been typed it will fire the below method
SearchCompany();
}
}
// This method is fired by the above property everytime a character is typed into the textbox
// What this method is meant to do is wait 1000 microseconds before it fires the filter
// However I need the timer to be reset every time a character is typed,
// Even if it hasn't reached 1000 yet
// But it doesn't do that. It continues to count before triggering the filter
private async void SearchCompany()
{
bool wait = true;
while (wait == true)
{
await Task.Delay(1000);
wait = false;
}
CompanyView.Filter = CompanyFilter;
}
// And this is the filter
private bool CompanyFilter(object item)
{
company company = item as company;
return company.title.Contains(SearchCompanyTitle);
}
So that's my problem. I need the filter to fire only when the timer hits 1000 and not before. At the same time I need the timer to go back to 0 every time the method is fired by the property. Clearly I'm not doing it right. Any ideas?

Sounds like a perfect candidate for binding Delay:
<TextBox Text="{Binding SearchCompanyTitle, Delay=1000}"/>

One solution could be to use the System.Threading.Timer class.
You can give it a callback to be called when the time set is elapsed.
Put the filter method as the callback and reset the timer's time on every key stroke.
You can find an example here.
--EDIT--
I didn't see that you were using WPF, Sinatr answer is the correct one, just use binding delay

Problem with C#, Listbox and GUI

i'm trying to update/paint a listbox in real time, but i'm having some problems.
I got a button to start the process of populating the listbox button_traceroute_Click.
My problem is that the listbox is only painted/updated when the whole process (button click) has ended, i wanted the the items to be inserted(viewed) one by one. I already tried using ListBox.Update() but nothing happened.
(this is a traceroute)
private void button_traceroute_Click(object sender, EventArgs e)
{
String target;
int i = 0;
target = textBox_target.Text;
Mydata data = new Mydata();
TraceRoute traceroute = new TraceRoute();
while (i < 50 && !data.getReached() && !data.getError()) // i = hop count
{
data = traceroute.startTrace(target, data, i);
listBox_trace.Items.Add(data.getOutput());
i++;
}
}
data.getOutput() returns (string) something like: "Hop X: 165.468.354.4 -> 50 ms" or "Hop X: Timeout"
Mydata{
bool Finish flag;
bool Error flag;
int badcounter;
String output;
}
For now im populating the listbox with Strings, but the objective is to use a object.

You need to put the long running operation on it's own thread. then report the progress back to the UI intermittently.
You can see an example how to do this in another post of mine here.

Also, you can use the BeginUpdate and EndUpdate method to speed up the repainting of the listbox. When BeginUpdate is called, any pending paint to the listbox is suspended, likewise, EndUpdate resumes the painting, this can help making your listbox look as if it is fast in loading the data into it and minimizes the number of painting to it when adding the data.
Hope this helps,
Best regards,
Tom.

Try this:
data = traceroute.startTrace(target, data, i);
listBox_trace.Items.Add(data.getOutput());
Application.DoEvents();
i++;
Its not ideal - Michael G's answer is best, but this could work as a quick fix.

C# WinForms: Waiting for a button press inside an infinite loop

I'm making a simple Guess-The-Number game with a GUI. I need to wait on a loop waiting for the user to input a number in a text box and press "OK". How do I wait for an event inside a loop?
Note: I don't want message boxes. This is done in the main window, hence the need to wait for input.
EDIT: I should have explained myself better. I know that there's a loop inside the GUI. What I want is another loop inside a method. Maybe there's a better way to do this. I could code stuff inside the button's event handler, now that I think about it. Although I'd need global variables. Whataver, I'll think about it, but I hope my question is clearer now.
EDIT 2: Sorry that my question wasn't clear and the edit didn't do much help. First of all, the code is too big to be posted here. I'd probably have to post a screenshot of the GUI, so it wouldn't be of much use. Basically, I have two fields, "Max number" and "Number of allowed guesses". The user enters these two and clicks "Play". A new panel becomes available, with a text box and a "Guess" button. The user enters a guess, and the program checks to see if it's correct.
The purpose of the second infinite loop is to avoid global variables. See, each time the user clicks "Play", the game has to generate a new random number as the correct guess. If everything is done inside a method, no problem. But if the "Guess" button's event handler is called multiple times, the number has to be stored as an instance variable of the Form. Sure, it's not big deal, but I think the number should be a property of the method directing the current game, not of the Form.
I'd also have to keep track of the remaining number of guesses outside of the method. Again, it's no big deal. I just want to avoid globals if I can.
Again, I'm sorry that my question wasn't too clear. I'm kind of tired, and I didn't feel like writing too much. If this still isn't clear, then don't bother. I'll think of something.

C# automatically loops infinitely waiting for events until your form is closed. You just need to respond to the button click event.

Jason Down's suggestion is wise, create a new GuessingGame class and add it to your project. I know you're worried about "global variables" (which everyone is taught in school never to use unless you absolutely have to), but think about your design specifications for a minute.
But if the "Guess" button's event handler is called multiple times, the number has to be stored as an instance variable of the Form. Sure, it's not big deal, but I think the number should be a property of the method directing the current game, not of the Form.
As an alternative, store an instance of your GuessingGame class in the form. This is not a global variable! You said so yourself, the point of the game is keep track of the guesses and generate new numbers to guess every time "Play" is clicked. If you store an instance of the game in the form then open another form (e.g. a Help or About box), then the game's instance would not be available (thus, not global).
The GuessingGame object is going to look something like:
public class GuessingGame
{
private static Random _RNG = new Random();
private bool _GameRunning;
private bool _GameWon;
private int _Number;
private int _GuessesRemaining;
public int GuessesRemaining
{
get { return _GuessesRemaining; }
}
public bool GameEnded
{
get { return !_GameRunning; }
}
public bool GameWon
{
get { return _GameWon; }
}
public GuessingGame()
{
_GameRunning = false;
_GameWon = false;
}
public void StartNewGame(int numberOfGuesses, int max)
{
if (max <= 0)
throw new ArgumentOutOfRangeException("max", "Must be > 0");
if (max == int.MaxValue)
_Number = _RNG.Next();
else
_Number = _RNG.Next(0, max + 1);
_GuessesRemaining = numberOfGuesses;
_GameRunning = true;
}
public bool MakeGuess(int guess)
{
if (_GameRunning)
{
_GuessesRemaining--;
if (_GuessesRemaining <= 0)
{
_GameRunning = false;
_GameWon = false;
return false;
}
if (guess == _Number)
{
_GameWon = true;
return true;
}
else
{
return false;
}
}
else
{
throw new Exception("The game is not running. Call StartNewGame() before making a guess.");
}
}
}
This way, all the data related to the game is encapsulated within the class. Hooking up the events is easy in the codebehind of the form:
GuessingGame game = new GuessingGame();
private void btnPlay_Click(object sender, EventArgs e)
{
int numberOfGuesses = Convert.ToInt32(txtNumberOfGuesses.Text);
int max = Convert.ToInt32(txtMax.Text);
game.StartNewGame(numberOfGuesses, max);
}
private void btnGuess_Click(object sender, EventArgs e)
{
int guess = Convert.ToInt32(txtGuess.Text);
bool correct = game.MakeGuess(guess);
if (correct)
lblWin.Visible = true;
if (game.GameEnded)
{
// disable guess button, show loss label
}
}

You should probably look for a book to actually learn windows programming.
The very basics:
1) There is already an infinite loop deep down in the windows code somewhere. Any windows program is constantly looping and scanning for input.
2) Once input is found, this loop fires off an Event.
3) Your mission, should you choose to accept it, is to write event handlers to handle those events.

you are most likely doing it wrong as it has already been pointed out, but you can use this
Application.DoEvents();
to process events when you are on an actual loop
to do it the right way
- don't use a loop
- use an edit box for the input, then a button
- implement the button onclick event

Yes, and What if I am waiting for Speech events, it could happen anytime event when a function is running, I need to handle that without recursively call a function