property enabled of button in uialertview

I crea开发者_Python百科te a uialertview with two button and a textfield, and I want a disable the button "Ok" if the textfield is empty. How I can get the uibutton object, to change is enabled status.

You can use the enabled property inherited from UIControl:

for(UIView *view in alertView.subviews) {
    if([view isKindOfClass:[UIButton class]]) {
      ((UIButton *) view).enabled = NO;
    }
}

For the sake of reusability, this becomes even simpler when you have a category on NSArray which retrieves objects of a given class:

@implementation NSArray (JRAdditions)

- (NSArray *)objectsOfClass:(Class)cls {
   NSParameterAssert(cls);
   NSMutableArray *array = [@[] mutableCopy];
   for(id obj in self) if([obj isKindOfClass:cls]) [array addObject:obj];
   return [array copy];
}

@end

Your code can now look like this:

[[alertView.subviews objectsOfClass:[UIButton class]] enumerateObjectsUsingBlock:^(UIButton *obj, NSUInteger index, BOOL *stop) {
    obj.enabled = NO;
}];

Since iOS 5, you can do this in the UIAlertViewDelegate instance.

-(BOOL) alertViewShouldEnableFirstOtherButton:(UIAlertView *)alertView
{
   return [[alertView textFieldAtIndex:0].text length] > 0;
}