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I have a block of code that repeats using a "for" loop, and each loop constructs a form to display some text. Some thing like the shorthand code below. 

Main() { For (int x: x<=20; x++) { createform(string[x]); } }

So for each loop a different string is passed to a method that will construct a form as below.

createform void (string input_) { ... code to build form and add a button "cancelbutton" form.text = intput_ .... form.cancelbutton.Click += // and I want this to cause the original loop to end.... }

No I know I could use the button to make int x greater than 20 and that would end the loop, but I don't actually know what the max value will be as this is dynamic. Again I could work this out and do he same thing but it seems a bit "messy".

Is there a neater way to cause the button click to exit the loop. How about if the Createform method is in a separate class to main, does that make any difference?

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    That loop will finish before anyone can Click that button Commented Oct 4, 2011 at 16:21
  • not if there is a show dialog statment to display the form it wont :) Commented Oct 4, 2011 at 16:23
  • So really it should be called "CreateAndShowForm"? Commented Oct 4, 2011 at 16:30
  • @ShellShock or, maybe have actual code, rather than half psuedo code and half illegal syntax? Commented Oct 4, 2011 at 16:31

7 Answers 7

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If your loop runs from 0 to 20 (or even over 9000) the user won't be able to click the cancel button in time. In fact, since it is all on one thread, the loop will finish before the UI responds to the click, but maybe I have misunderstood. Could you just have a boolean flag which you check each time you enter the loop and set it to false once the user clicks the button?

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I would guess the simple loop was for instructional purposes only. I could be wrong.
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Just add a variable and code the click event:

static bool clicked; Main() { clicked = false; For (int x: (x<=20) && !clicked; x++) { createform(string[x]); } } public static void Click_Detector(object sender, EventArgs e) { clicked = true; }

Your routine would need to do something like this:

createform void (string input_) { ... code to build form and add a button "cancelbutton" form.text = intput_ .... form.cancelbutton.Click += MainClass.Click_Detector; }
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Cheers that does seem the logical way and string forward way to do it. I am sure Tigran method below would work to, using the method to return the True/False. Boh seem to make prefect sence. :)
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You shouldn't be using a loop to create each form. Assuming you have a submit button. Every time the user clicks submit, you should explicitly show the next form. That way, if a user clicks cancel, you don't have to worry about the rest of the forms.

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in this case clicking submit sends an array of strings to the user to be displayed, (form is a glorified ext box). dont want them to have to click submit inbetween each form, either close the current form and the next one comes up, or click cancle and break out.
@DevilWAH, my instructions still work. Instead of showing the next form after the submit button, do it after whatever action closes the current form.
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The first solution that comes to my mind is: return value of the method True/False and in foreach check for its return value, if False=> break.

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@DevilWAH: if your function parameter vary, execution time of that function vary too. If you want as fast feedback to user's action as you can, you shiuld go as deep on stsck as you can.
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Your psuedo code isn't indicating how you are showing the form in CreateForm(). Is this going to be a modal or non modal? It would have to be modal, otherwise, you'd just keep creating forms until the cows come home. Remember, adding a handler to the click button doesn't actually execute the handler method until the click button is clicked.

Presumably your click event handler could set the value of x to be greater than 20, but since you said you're not sure what the maximum is, you could have a do loop governed by a boolean flag, and your createform() could set the state of the flag.

I'd recommend rethinking your problem space, as this overall approach seems really convoluted. I don't understand your UI, but it seems like your intent is to have the user control the exit of an infinite loop, like those old RPGs that ask you "Do you want to go on an adventure Yes/No", and it would continue asking you until you hit "Yes". These are pointless and confusing.

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no endlles but could be 10 or 20 cycles. there is far more to each loop than simple displaying a form, this is purely for the user to check the out come of each cycle (loop bulk creates cionfiguration outputs from date inputted via varuious methods). so each config is displayed, with three choises, "SAVE" "Remove" and "cancel" Ie. some one entered total the worng thing and i need to go back and fix it before I carry on.
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Add a boolean to the class and have the click event set the boolean value. Then you can break from the loop. However, if your real world use is the question above I would agree with the answer given by mikerobi.

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Yeah your code sample explains it better I was in a hurry to get to a meeting so I skipped the sample. I would probably have exposed an event on the ShowForm class rather than having the event call back to a static method on the calling class. Just to separate concerns.
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One good solution would be to use the CancelAsync() method of the BackgroundWorker class: http://msdn.microsoft.com/en-us/library/system.componentmodel.backgroundworker.cancelasync.aspx

If you don't want to work with a separate thread to improve the performance, that I don't recommend, is to set a class level boolean value when the button clicked, then the for loop checks that boolean value in each next process.

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