Question

I am trying to add UIRefreshControl for IOS 6.

#define SYSTEM_VERSION_LESS_THAN_OR_EQUAL_TO(v)     ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] != NSOrderedDescending)

if(SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(@"6.0")) {
    UIRefreshControl *refresh = [[UIRefreshControl alloc] init];
    refresh.attributedTitle = [[NSAttributedString alloc] initWithString:@"Pull to Refresh"];
    [refresh addTarget:self action:@selector(refreshView:)
      forControlEvents:UIControlEventValueChanged];
    self.refreshControl = refresh;
}

and

if (NSClassFromString(@"UIRefreshControl") != Nil) {
    UIRefreshControl *refresh = [[UIRefreshControl alloc] init];
    refresh.attributedTitle = [[NSAttributedString alloc] initWithString:@"Pull to Refresh"];
    [refresh addTarget:self action:@selector(refreshView:)
      forControlEvents:UIControlEventValueChanged];
    self.refreshControl = refresh;
}

but getting the error

dyld: Symbol not found: _OBJC_CLASS_$_UIRefreshControl
Referenced from: /Users/office/Library/Application Support/iPhone    Simulator/4.3.2/Applications/DD532E42-77F9-471C-AA48-7F9EAE9268C6/Verizon.app/Verizon
Expected in:   /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/i PhoneSimulator4.3.sdk/System/Library/Frameworks/UIKit.framework/UIKit

i am using IOS 6 SDK and running on iPhone 4.3 Simulator.

When i remove the code

    UIRefreshControl *refresh = [[UIRefreshControl alloc] init];
    refresh.attributedTitle = [[NSAttributedString alloc] initWithString:@"Pull to Refresh"];
    [refresh addTarget:self action:@selector(refreshView:)
      forControlEvents:UIControlEventValueChanged];
    self.refreshControl = refresh;

everything works for iPhone 4.3 Simulator. Interestingly code inside

if(SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(@"6.0")) {  }

never gets called when on iPhone 4.3 Simulator, not sure why the error. Please Help!!

Answer 1

Definitely go with the second style, i.e.:

if (NSClassFromString(@"UIRefreshControl") != nil) {
    ...
}

As for the error you are getting, you should be able to stop that by setting UIKit to “Optional” within the “Link binary with libraries” section of the project’s “Build Phases” settings.

It should mark it as optional for you as it notices you’re using a class that’s only available in iOS 6, but looks like it’s not in your case for some reason.