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Back button control in windows phone app

I am developing a windows phone 8 app. I want to control the back button of the phone for doing specific task. I want that when user press the back button in specific page it will not navigate to the previous page but to the page which I want. Is their any way to control the hardware back button present in phone?

In Silverlight apps (WP7, WP8, WP8.1) you do this:
protected override void OnBackKeyPress(CancelEventArgs e)
{
// put any code you like here
MessageBox.Show("You pressed the Back button");
e.Cancel = true;
}
That will work in all Windows Phone versions if you're using Silverlight.
If you're using WinRT for Windows Phone 8.1, it is a bit different:
Open NavigationHelper.cs and make this modification:
private void HardwareButtons_BackPressed(object sender, Windows.Phone.UI.Input.BackPressedEventArgs e)
{
if (this.GoBackCommand.CanExecute(null) && !e.Handled)
{
e.Handled = true;
this.GoBackCommand.Execute(null);
}
}
Now in your app page (the page that will be open when the back button is pressed), add the following namespace:
using Windows.Phone.UI.Input;
Add this handler to the constructor method of your page:
HardwareButtons.BackPressed += OnBackPressed;
Then add this method:
private async void OnBackPressed(object sender, Windows.Phone.UI.Input.BackPressedEventArgs e)
{
e.Handled = true;
// add your own code here to run when Back is pressed
}
Note: in both cases, the 'e.Handled = true' line tells the OS that the back button press has been handled, and therefore the OS will not action the default behaviour. If you remove that line your own code will run, and the OS will also do its own backwards navigation.
Be mindful of Rowland's comment about overriding the Back button - if you're not navigating intuitively you will confuse the user and risk your game being rejected (if you just need to control a pause screen or menu it will be fine, but if you implement something gimmicky like using the Back button as a game control you'll be in trouble).
My blog has the same answer with a bit more detail if you need it:
http://grogansoft.com/blog/?p=572

Whilst it possible to cancel the navigation event, and permissable in a game to present a pause screen or similar, generally it is not allowed to use the back button for anything other than backward navigation in an app; Per requirement 5.2.4 of the Technical certification requirements for Windows Phone
To maintain a consistent user experience, the Back button must only be used for backwards navigation in the app.
If you are creating a XAML app where it is permissible to cancel a "back" operation, such as per 5.2.4.4 of the Technical certification requirements for Windows Phone
:
For games, when the Back button is pressed during gameplay, the game can choose to present a pause context menu or dialog, or it can navigate the user to the prior menu screen.
Then you can implement this by overriding the OnNavigatingFrom method on your page, and set the Cancel property of the NavigatingCancelEventArgs, so something like this example from Frame, page, and navigation features for Windows Phone 8:
protected override void OnNavigatingFrom(NavigatingCancelEventArgs e)
{
base.OnNavigatingFrom(e);
// If the navigation can be cancelled, ask the user if they want to cancel
if (e.IsCancelable)
{
MessageBoxResult result = MessageBox.Show("Do you want to stay here?", "Confirm Navigation from Page", MessageBoxButton.OKCancel);
if (result == MessageBoxResult.OK)
{
// User wants to stay here
e.Cancel = true;
return;
}
}
}
Of course, you may choose to implement the prompt differently, but that should illustrate how it is possible.

How to prevent OpenTK.GameWindow from closing

I have a game I've written in OpenTK but am looking for a way to add a handler to the close button of the game window without actually closing the game (e.g. invoking a "do you want to save before you quit?" sort of dialog). I can't seem to find any event handler or documentation that accomplishes this.

You can override the OnClosing method and show your message box there. If the user does not want to close, you can use e.Cancel = true, which will stop the form from closing:
protected override void OnClosing(CancelEventArgs e)
{
// ... show message box
if (/* wants to save*/)
{
// Cancel closing, the player does not want to exist
e.Cancel = true;
}
base.OnClosing(e);
}

How to force close button to terminate all childforms?

I have program that opens subwindows inside of it (mdi.parent). I have made component that is in one window under it, however, i want that that window never actually disposed after its created because i want to keep only one instance of it.
This can be made with code:
// This prevents this window disposing from window close button, we want always show one and only
// one instance of this window.
FormClosing += (o, e) =>
{
Hide();
e.Cancel = true;
};
However, after this there is problem, closing program requires pressing close button press twice. First press closes subwindow and second terminates program. How this can be get around?
I am working with Winforms.

As Habib said, you can call Application.Exit, but:
The Form.Closed and Form.Closing events are not raised when the
Application.Exit method is called to exit your application
If this is important to you, you can do something like this (MDI parent code):
private Boolean terminating;
protected override void OnClosing(CancelEventArgs e)
{
if (!terminating)
{
terminating = true;
Close();
}
base.OnClosing(e);
}

Call Application.Exit() in the form close event.
Application.Exit - MSDN
Informs all message pumps that they must terminate, and then closes
all application windows after the messages have been processed.

The code inside of your FormClosing event handler method is a bit too terse. It does its job of preventing the user from closing the form, but as you've also noticed, it prevents you from closing the form programmatically as well.
This is easily solved by testing the value of the CloseReason property of the FormClosingEventArgs that are passed in each time the event is raised.
These will tell you the reason why the form is attempting to close. If the value is CloseReason.UserClosing, then you want to set e.Cancel to true and hide the form. If the value is something else, then you want to allow the form to continue closing.
// This prevents this window disposing when its close button is clicked by the
// user; we want always show one and only one instance of this window.
// But we still want to be able to close the form programmatically.
FormClosing += (o, e) =>
{
if (e.CloseReason == CloseReason.UserClosing)
{
Hide();
e.Cancel = true;
}
};

Use This
Form[] ch = this.MdiChildren;
foreach (Form chfrm in ch)
chfrm.Close();

You can use Application.Exit if there is no processing happening when the application is closed. Otherwise, you can check Application.OpenForms collection in MDI parent's closing event and close all the other forms that are open.

Cancelling OnFormClosing and task manager

According to MSDN
http://msdn.microsoft.com/en-us/library/system.windows.forms.form.onformclosing.aspx
I am trying to block a user from closing a form (except for windows shutting down).
protected override void OnFormClosing(FormClosingEventArgs e)
{
if (e.CloseReason != CloseReason.WindowsShutDown)
{
e.Cancel = true;
wiggle();
}
base.OnFormClosing(e);
}
When closing from the task manager "End task" button, the window do not closes as expected but I get an error after a few seconds
How does windows determines if a program is responding or not !
All the form does is nothing...

Task Manager asked the program to close and it didn't. At least in WinXP, the Task Manager doesn't like that and pops up the "Not Responding" window after several seconds.
It is typically a bad design to try and prevent app closings, especially this way. The next tab on TaskMan will bypass any such checks.

Alert on Back Key Press, Confirm Exit

I'm writing a windows phone app, and I want to know how to alert and make sure the that user really wants to exit the app on the back key press. Pretty simple.
Thanks.

I assume your navigation is set up such that the user can only exit from the first page. If so, in that page, you can override the OnBackKeyPress event and cancel the button press. I haven't tested this code, but seems like it should work:
protected override void OnBackKeyPress(CancelEventArgs e)
{
if(MessageBox.Show("Are you sure you want to exit?","Exit?",
MessageBoxButton.OKCancel) != MessageBoxResult.OK)
{
e.Cancel = true;
}
}
Edit - I'll leave this here as an example of overriding the back button, but the correct answer in this context is to not implement the feature.

While the previous answer about cancelling OnBackKeyPress may technically work, it could cause your app to fail certification requirements. See the following link:
http://msdn.microsoft.com/en-us/library/hh184840(v=VS.92).aspx
5.2.4.2 – Back Button: First Screen
Pressing the Back button from the first screen of an application must close the application.
I would recommend not implementing this functionality.