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    <p>Simple example...</p> <p>Let's say the child view controller has a <code>UISlider</code> and we want to pass the value of the slider back to the parent via a delegate.</p> <p>In the child view controller's header file, declare the delegate type and its methods:</p> <p><strong>ChildViewController.h</strong></p> <pre><code>#import &lt;UIKit/UIKit.h&gt; // 1. Forward declaration of ChildViewControllerDelegate - this just declares // that a ChildViewControllerDelegate type exists so that we can use it // later. @protocol ChildViewControllerDelegate; // 2. Declaration of the view controller class, as usual @interface ChildViewController : UIViewController // Delegate properties should always be weak references // See http://stackoverflow.com/a/4796131/263871 for the rationale // (Tip: If you're not using ARC, use `assign` instead of `weak`) @property (nonatomic, weak) id&lt;ChildViewControllerDelegate&gt; delegate; // A simple IBAction method that I'll associate with a close button in // the UI. We'll call the delegate's childViewController:didChooseValue: // method inside this handler. - (IBAction)handleCloseButton:(id)sender; @end // 3. Definition of the delegate's interface @protocol ChildViewControllerDelegate &lt;NSObject&gt; - (void)childViewController:(ChildViewController*)viewController didChooseValue:(CGFloat)value; @end </code></pre> <p>In the child view controller's implementation, call the delegate methods as required.</p> <p><strong>ChildViewController.m</strong></p> <pre><code>#import "ChildViewController.h" @implementation ChildViewController - (void)handleCloseButton:(id)sender { // Xcode will complain if we access a weak property more than // once here, since it could in theory be nilled between accesses // leading to unpredictable results. So we'll start by taking // a local, strong reference to the delegate. id&lt;ChildViewControllerDelegate&gt; strongDelegate = self.delegate; // Our delegate method is optional, so we should // check that the delegate implements it if ([strongDelegate respondsToSelector:@selector(childViewController:didChooseValue:)]) { [strongDelegate childViewController:self didChooseValue:self.slider.value]; } } @end </code></pre> <p>In the parent view controller's header file, declare that it implements the <code>ChildViewControllerDelegate</code> protocol.</p> <p><strong>RootViewController.h</strong></p> <pre><code>#import &lt;UIKit/UIKit.h&gt; #import "ChildViewController.h" @interface RootViewController : UITableViewController &lt;ChildViewControllerDelegate&gt; @end </code></pre> <p>In the parent view controller's implementation, implement the delegate methods appropriately.</p> <p><strong>RootViewController.m</strong></p> <pre><code>#import "RootViewController.h" @implementation RootViewController - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath { ChildViewController *detailViewController = [[ChildViewController alloc] init]; // Assign self as the delegate for the child view controller detailViewController.delegate = self; [self.navigationController pushViewController:detailViewController animated:YES]; } // Implement the delegate methods for ChildViewControllerDelegate - (void)childViewController:(ChildViewController *)viewController didChooseValue:(CGFloat)value { // Do something with value... // ...then dismiss the child view controller [self.navigationController popViewControllerAnimated:YES]; } @end </code></pre> <p>Hope this helps!</p>
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    1. POHow do I set up a simple delegate to communicate between two view controllers?
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    1. USSimon Whitaker
    1. USSimon Whitaker
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    1. POHow do I set up a simple delegate to communicate between two view controllers?
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    1. COHow though does the parent register as the delegate of the child?
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    2. COBy calling `detailViewController.delegate = self;` (it's in `-tableView:didSelectRowAtIndexPath:` in the above code snippet.
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      1. USSimon Whitaker
    3. COThanks. If the ChildViewController is delegate to UITableView, where should the UITableView methods be? In the child or the parent?
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