UISwitch does sometimes not send UIControlEvents - objective-c

Question

I have a model object which includes a boolean flag. I want to show the value of the flag using a UISwitch. The value can be changed in two ways:
First by the user by toggling the switch. I register the UIControlEventTouchUpInside for that. I also tried UIControlEventValueChanged – it has the exact same effect.
Second by some external state change. I use a timer to check for that state change and set the on property of the switch accordingly.
However, setting the value of the switch in the timer method has the effect that the touchUpInside action is sometimes not triggered even though the user has touched the switch.
So I face the following problem: If I set the switch state in the timer when the state changes externally, I loose some state changes from the user. If I don't use the timer I get all state changes from the user. However, I miss all the external state changes, then.
Now I have run out of ideas. How can I achieve what I want, getting both types of state changes in the model and reflected them correctly in the switch view?
Here is a minimal example that shows the problem. I have replaced the model object by a simple boolean flag, and in the timer I don't change the flag at all, I just call setOn:animated:. I count the invocations of the action method. Like that I can easily find out how many touches were missed:
#import "BPAppDelegate.h"
#import "BPViewController.h"
#implementation BPAppDelegate {
NSTimer *repeatingTimer;
}
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions: (NSDictionary *)launchOptions
{
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
BPViewController *viewController = [[BPViewController alloc] init];
self.window.rootViewController = viewController;
[self.window makeKeyAndVisible];
[self startTimer];
return YES;
}
- (void) startTimer {
repeatingTimer = [NSTimer scheduledTimerWithTimeInterval: 0.2
target: self.window.rootViewController
selector: #selector(timerFired:)
userInfo: nil
repeats: YES];
}
#end
#import "BPViewController.h"
#implementation BPViewController {
UISwitch *uiSwitch;
BOOL value;
int count;
}
- (void)viewDidLoad
{
[super viewDidLoad];
value = true;
uiSwitch = [[UISwitch alloc] init];
uiSwitch.on = value;
[uiSwitch addTarget:self action:#selector(touchUpInside:) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:uiSwitch];
}
- (void)touchUpInside: (UISwitch *)sender {
count++;
value = !value;
NSLog(#"touchUpInside: value: %d, switch: %d, count: %d", value, sender.isOn, count);
}
- (void) timerFired: (NSTimer*) theTimer {
NSLog(#"timerFired: value: %d, switch: %d, count: %d", value, uiSwitch.isOn, count);
// set the value according to some external state. For the example just leave it.
[uiSwitch setOn:value animated:false];
}
#end

Answer 1

Use UIControlEventValueChanged to determine when the switch has been toggled (programmatically or by the user). Don't use touchUpInside. Also touchUpInside doesn't work well for when the user drags the UISwitch.
Also, don't replicate a property (e.g. your value property) that is already maintained by the UISwitch (i.e. the "on" property)...its redundant and will just get you into trouble

Answer 2

EDIT: The following code does exactly what you want, if not exactly the way you want it. If insures that both timer changes and touch changes to the control receive an action method. The method is only going to be sent once per change, which is hopefully what you want.
Note the switch to UIControlEventValueChanged.
[sw addTarget:self action:#selector(touched:) forControlEvents:UIControlEventValueChanged];
- (void) timerFired: (NSTimer*) theTimer
{
// set the value according to some external state. For the example just leave it.
BOOL oldOn = sw.on;
BOOL newOn = YES;
[sw setOn:newOn];
if(newOn != oldOn) {
for(id target in [sw allTargets]) {
for(NSString *action in [sw actionsForTarget:target forControlEvent:UIControlEventValueChanged]) {
[target performSelector:NSSelectorFromString(action) withObject:self];
}
}
}
}
EDIT2:
I [original poster] just saw the new code in your answer and tried it out. I am not sure it is doing exactly what I want. However, I am not sure if I understand it correctly. I don't want to do exactly the same thing in both cases.
Q: When the user touches the switch I want to toggle the boolean value in the model. I not necessarily need to change the switch programmatically because it is done automatically by touching it anyway. I want to count the touches to make sure none are lost.
A: Well, that's not really possible. However, you can certainly add a counter to the action method and see if the taps you make equal the counter. When the user taps the switch, then "sender == theSwitch". If you send the action method otherwise, you can use a different sender (to differentiate them).
If I get the timer event in my minimal example I just want to leave the boolean value like it currently is. However, I need to set the switch state programmatically so that the view reflects the correct model state. – Bernhard Pieber 3 mins ago
Thats fine - but you keep saying you want the action method called. This code does that. If you misstated that, and you don't want the action method called, then delete the "if" block.
- (void)insureValueIs:(BOOL)val
{
BOOL oldVal = sw.on;
if(val != oldVal) {
for(id target in [sw allTargets]) {
for(NSString *action in [sw actionsForTarget:target forControlEvent:UIControlEventValueChanged]) {
[target performSelector:NSSelectorFromString(action) withObject:self];
}
}
}
}
Of course, I do want to achieve the same thing: That the model state is correctly reflected in the view. Does that make sense?
Frankly, you have not done a good job in describing EXACTLY what you want, and I keep responding to your comments, but even now I am still not totally clear. I believe you have all the information you need here to do whatever it is you want.

Answer 3

Your timer is firing so often it probably prevents the switch ever finishing the animated transition to the alternative value, so it never sends the valueChanged event message. You are setting the value to YES every 0.2 seconds which is faster, I think, than the duration of the animation that occurs when the user taps the switch.

Answer 4

My original code works as expected in iOS 7. So it seems to have been a bug in iOS 6.