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Posted 20 Dec 2010

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Hourglass Mouse Cursor Always Changes Back to its Original Image. How?

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21 Dec 2010CPOL1 min read
IDisposable with “using” block helps in all cases
Testing and debugging UI code, I am often faced with such a situation, when the mouse cursor is changed to Hourglass, but not changed back.
Sometimes, it happened to my own code as well.

The mouse cursor is supposed to be changed back to its original or default image after the procedure which could cause a delay if UI response is already completed (or failed). Sometimes it is not changed back because this procedure fails due to exception or some other reason. Sometimes the code used to set mouse cursor to its original image is simply forgotten.

As a result, I came to a simple pattern which helps to avoid such situation in all cases. I used it in several different UI systems. Now I'll show how it is implemented with .NET. The idea is using helper class implementing IDisposable.

This is a WPF implementation written in C#:

C#
namespace SA.Universal.UI {
    using IDisposable = System.IDisposable;
    using FrameworkElement = System.Windows.FrameworkElement;
    using Cursor = System.Windows.Input.Cursor;
    using Cursors = System.Windows.Input.Cursors;
    using Debug = System.Diagnostics.Debug;

    public class WaitCursorIndicator : IDisposable {

        public WaitCursorIndicator(FrameworkElement owner) {
            this.Onwer = owner;
            Debug.Assert(
                owner != null,
                "WaitCursorIndicator expects non-null argument");
            if (owner == null) return;
            Previous = owner.Cursor;
            owner.Cursor = Cursors.Wait;
        } //WaitCursorIndicator

        void IDisposable.Dispose() {
            if (this.Onwer == null) return;
            this.Onwer.Cursor = Previous;
        } //IDisposable.Dispose

        FrameworkElement Onwer;
        Cursor Previous;

    } //class WaitCursorIndicator

} //namespace SA.Universal.UI


With System.Windows.Forms, it is implemented in a very similar way:

C#
namespace SA.Universal.UI {
    using System.Windows.Forms;
    using IDisposable = System.IDisposable;
    using Debug = System.Diagnostics.Debug;

    public class WaitCursorIndicator : System.IDisposable {

        public WaitCursorIndicator(Control owner) {
            this.Owner = owner;
            Debug.Assert(
                owner != null,
                "WaitCursorIndicator expects non-null argument");
            if (owner == null) return;
            Previous = this.Owner.Cursor;
            owner.Cursor = Cursors.WaitCursor;
        } //WaitCursorIndicator

        void IDisposable.Dispose() {
            if (Owner == null) return;
            Owner.Cursor = Previous;
        } //IDisposable.Dispose

        Control Owner;
        Cursor Previous;

    } //class WaitCursorIndicator

} //namespace SA.Universal.UI


The usage looks identical for WPF and System.Windows.Forms:

C#
using(new WaitCursorIndicator(owner)) {
   //... some long-running code here
} //end using


In this code snippet, owner is most typically a form or a window.

This way, mouse cursor is changed back no matter what, even if an exception is thrown.
On exit from the "using" block, WaitCursorIndicator.Dispose is always called. In fact, using this "using" block is just syntactic sugar functionally strictly equivalent to the try-finally block with Dispose called in the finally section.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Sergey Alexandrovich Kryukov
Architect
United States United States
No Biography provided

Comments and Discussions

 
GeneralMessage Removed Pin
19-Dec-10 7:05
mvaSergey Alexandrovich Kryukov19-Dec-10 7:05 
GeneralYou're right, of course, but in real life people make mistak... Pin
Sergey Alexandrovich Kryukov19-Dec-10 7:00
mvaSergey Alexandrovich Kryukov19-Dec-10 7:00 
GeneralI always thought that if a code changed the mouse pointer, t... Pin
DaveAuld18-Dec-10 21:25
professionalDaveAuld18-Dec-10 21:25 
GeneralRe: I always thought that if a code changed the mouse pointer, t... Pin
NGErndt10-Jul-20 14:13
MemberNGErndt10-Jul-20 14:13 
QuestionRe: I always thought that if a code changed the mouse pointer, t... Pin
Sergey Alexandrovich Kryukov30-Jan-21 10:00
mvaSergey Alexandrovich Kryukov30-Jan-21 10:00 
AnswerRe: I always thought that if a code changed the mouse pointer, t... Pin
DaveAuld30-Jan-21 21:16
professionalDaveAuld30-Jan-21 21:16 
AnswerIt was just the relocation of my misplaced post Pin
Sergey Alexandrovich Kryukov31-Jan-21 3:58
mvaSergey Alexandrovich Kryukov31-Jan-21 3:58 
AnswerYour Astrophotography channel Pin
Sergey Alexandrovich Kryukov31-Jan-21 4:09
mvaSergey Alexandrovich Kryukov31-Jan-21 4:09 
GeneralRe: Your Astrophotography channel Pin
DaveAuld31-Jan-21 4:19
professionalDaveAuld31-Jan-21 4:19 
Thanks Sergey,

I just started last year, but with covid spent more time at work offshore than behind my telescopes.

I just took receipt of another new scope an 11" Rasa so looking forward to getting that out of the box. I also get fed up having to set up and strip down all the gear everynight I wanted to image so have also taken receipt of an new prefab observatory, so looking forward to getting that built in the next few weeks.

I just find space fascinating. The sheer scale of it all is beyond comprehension.

So, few more things to get trying this year, new scopes, off axis guiding, multistar guiding, some new filters....and the list goes on!

Cheers,

AnswerRe: Your Astrophotography channel Pin
Sergey Alexandrovich Kryukov31-Jan-21 9:25
mvaSergey Alexandrovich Kryukov31-Jan-21 9:25 

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