Design pattern for UI controls' state management in iOS - iphone

Question

Similar to this question, but I am looking for a generic solution or design pattern or framework.
Q. How to add state management into all UI controls in my iOS app automatically without the need to rewrite the existing controls' class?
Example:
e.g. When I click on a UIButton, it will create a new UIWebView showing Google home page. That is easy, but problem arise when user sometimes.. click the button just too fast, so two webview will be displayed.
To solve this question, I would need to make a singleton class which contain the webview, and have a state variable isOpended and if it is true, reuse the existing webview instead of creating a new one.
But the problem is: If I want this behavior in other controls also, then I would need to create many many singleton classes..I am just thinking if there is better way to handle this without the new to re-invent the wheel.
Thanks.

Answer 1

I think you're solving the wrong problem here. Why don't you disable the button until the UIWebView is done processing. That way the user cannot click it twice.
- (IBAction)showMapHomepage:(UIButton*)sender
{
sender.enabled = NO;
[self taskThatTakesALongTimeWithCompletion:^{
sender.enabled = YES;
// Finish processing
}];
}

Answer 2

You are misinterpreting the best way to go about solving your problem. First of all, you should never find yourself in a situation where you are creating many many singletons. Singletons are a necessary evil, but you should not overuse nor abuse them. Here is a good post about singletons in objective-c.
There are numerous ways you could go about preventing a second UIWebView from being displayed when the user clicks your button.
As someone else stated, one solution would be to disable the button so that the user cannot "double-click" it. You do this using:
button.enabled = NO;
You could also hide your button using:
button.hidden = YES;
Or, in the header of the class that contains your UIButton, you could create a boolean that will handle the logic of whether or not the button has been pressed;
// declare this in your header
BOOL buttonPressed;
// this is the IBAction that your button hooks up to
- (IBAction)createWebViewButtonPressed:(id)sender {
if(!buttonPressed) {
buttonPressed = YES;
// insert code here to create your UIWebView
}
}
Again, there are numerous ways to accomplish what you are trying to do. You just have to determine which method is the best for you.

Answer 3

I agree with other answers that you should probably disable the control if you don't want it to be activated twice. However, if you do want an answer for your actual question about a generic pattern that you can use on all controls then you can use associated objects...
- (IBAction)buttonAction:(UIButton*)sender
{
NSString* webViewKey = #"AssociatedWebView";
// See if there is web view already
id webView = objc_getAssociatedObject(sender, webViewKey);
if(webView == nil)
{
// There is no existing web view, create it
webView = [self theWebView];
// Associate it with the button
objc_setAssociatedObject(sender, webViewKey, webView, OBJC_ASSOCIATION_RETAIN);
// Add the web view
[self.view addSubview:webView];
}
}
The above shows a generic way to associate an object to an instance of UIButton so you can check if it is already associated and re-use the existing one. I provide this answer in case you intend to use this in some other way that isn't fully described in your question, but in practice, you could use a property of your controller for the webView that lazy-loads the webView if it isn't already loaded.
If you really want to simulate the singleton style that you discuss in your question (so that you can have many UIButton instances that all share the same webView object if it already exists) then you could associate the webView onto the [UIButton class] object or even the [UIControl class] object instead of your specific instance. You would do that by replacing the sender with [UIControl class] in the code above.

Answer 4

One possible solution is to store a pointer to the webview in a property of the viewController. In the getter for the webview, create the webview if it doesn't exist already. The button action just need to display the webview, as it will just redisplay the webview if it already exist, and it will create the webview if it doesn't. When you are done with the webview, just set it to nil.