Reading Checkbox status from another thread

Question

Am trying to read the value of a checkbox from a BackgroundWorker in WPF:

This doesn't work:

bool? isSleepChecked = checkBoxSleep.Dispatcher.Invoke(DispatcherPriority.Normal, (ThreadStart)delegate{ return checkBoxSleep.IsChecked;});

Cannot convert anonymous method to delegate type 'System.Threading.ThreadStart' because some of the return types in the block are not implicitly convertible to the delegate return type

EDIT - Here is HB's answer expressed using a delegate instead of lambda which I find slightly more readable

bool? isSleepChecked = (bool?)checkBoxSleep.Dispatcher.Invoke(new Func<bool?>(delegate { return checkBoxSleep.IsChecked; }));

H.B. · Accepted Answer · 2014-08-14T13:01:03.193

6

Assign the variable instead, then you don't need a return.

bool? isSleepChecked;
checkBoxSleep.Dispatcher.Invoke(new Action(
    () => isSleepChecked = checkBoxSleep.IsChecked));

Alternatively you can use a delegate with return value (e.g. a Func<T>):

bool? isSleepChecked = checkBoxSleep.Dispatcher.Invoke(new Func<bool?>(
                            () => checkBoxSleep.IsChecked));

(Requires return type cast before .NET 4.5)

edited Aug 14 '14 at 13:01

answered Feb 13 '12 at 19:49

H.B.

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Thanks HB (and Douglas too). Very similar answers. I seem to prefer the Func answer.. and there is a typo.. should be: new Func – Dave Mateer Feb 13 '12 at 20:29
@DaveMateer: Was just about to fix that :) – H.B. Feb 13 '12 at 20:31
Cheers - put in the delegate version above. – Dave Mateer Feb 13 '12 at 20:47
@DaveMateer: Lambdas are awesome, spare you two keywords (and they have an arrow!). But each their own i suppose... – H.B. Feb 13 '12 at 20:48

score 2 · Answer 2 · answered Feb 13 '12 at 19:47

Your code will not compile because, whilst you are attempting to return a bool? from your delegate, ThreadStart has a return type of void.

The easiest approach in such cases would probably be to capture your isSleepChecked variable within a lambda expression and set it directly:

bool? isSleepChecked = null;
checkBoxSleep.Dispatcher.Invoke(new Action(() =>
{ 
    isSleepChecked = checkBoxSleep.IsChecked; 
}), 
    DispatcherPriority.Normal);

Reading Checkbox status from another thread

2 Answers2

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