c# - Changing Opacity With Reactive Extensions -

<rant>yes, know easier implement in wpf. hear lot. sadly, not possible. </rant>

i writing winforms app, , need "fade" control in & out. transparency impossible in winforms, trying use opacity: idea change alpha channel of each child control's forecolor property on period of time. seems perfect time work on reactive extensions!

my possible solution is:

private void fadeout() {    // our list of values alpha channel (255 0)    var range = enumerable.range(0,256).reverse().tolist();     // how long between each setting of alpha (huge value example only)    var delay = timespan.fromseconds(0.5);     // our "trigger" sequence, every half second    observable.interval(delay)         // paired values range - keep range           .zip(range, (lhs, rhs) => rhs)         // make onnext changes on ui thread           .observeon(synchronizationcontext.current)         // every time value rec'd sequence           .subscribe(               // set alpha value               onnext:changealphavalues,                // when we're done, hide control               oncompleted: () => visible = false,                // citizenry               onerror: failgracefully); }  // no need iterate controls more once - store them here private ienumerable<control> _controls;  private void changealphavalues(int alpha) {     // controls (via extension method)     var controls = _controls ?? this.getallchildcontrols(typeof (control));      // iterate controls , change alpha     foreach (var control in controls)        control.forecolor = color.fromargb(alpha, control.forecolor); } 

... looks impressive, doesn't work. impressive part doesn't work in two ways! gonna "far exceed" on next performance review if keep up. :-)

1. (not rx part of problem) alpha values don't seem make difference. despite setting values, display looks same.
2. if close window before sequence complete, following error:

system.invalidoperationexception unhandled message: unhandled exception of type 'system.invalidoperationexception' occurred in system.reactive.core.dll additional information: invoke or begininvoke cannot called on control until window handle has been created.

i assume cancellation token come in handy - have no idea how implement it.

i need guidance on:

how close window gracefully (i.e. without throwing error) if sequence still running, , how alpha values colors display after they're changed.

... or maybe wrong approach altogether.

i'm open other suggestions.

i can't winforms transparency part. maybe should split question in two.

but rx part, need cancel subscription when window closed. subscribe returns idisposable. should dispose of in closed event.

and, since assume fade animation might invoked multiple times before window closed, can make use of rx helper serialdisposable.

finally, interval returns count. can use simplify observable calculating desired alpha.

private serialdisposable _fadeanimation = new serialdisposable();  private void fadeout() {     // how long between each setting of alpha (huge value example only)     var delay = timespan.fromseconds(0.5);      _fadeanimation.disposable = observable         .interval(delay)         // 256 animation steps         .take(256)         // calculate alpha         .select(i => 255 - i)         .observeon(synchronizationcontext.current)         .subscribe(             // set alpha value             onnext:changealphavalues,              // when we're done, hide control             oncompleted: () => visible = false,              // citizenry             onerror: failgracefully); }  private void form1_closed() {     _fadeanimation.dispose(); }