Question

Alright, so to get going with Objective-C (I’m usually just an HTML PhoneGap kinda guy), I made a simple Magic 8 ball app. I’ve got it right now so that when I touch the screen, the ball “shakes” and takes a random response and puts it in a label. What I want to do is when the iPhone itself is shaked, the text is updated too.

Here’s my MainView.m:

#import "MainView.h"

@implementation MainView

- (void)motionEnded:(UIEventSubtype)motion withEvent:(UIEvent *)event {
 if (event.type == UIEventSubtypeMotionShake) {
  int rNumber = rand() % 26;
  switch (rNumber) {
                case 0:
                    shook.text = @"Never";
                    break;
            ....25 more entries.....
                default:
                    break;
           }
    }
 }

 - (IBAction)yesNo {
 [NSThread sleepForTimeInterval:0.75];
 int rNumber = rand() % 26;
 switch (rNumber) {
  case 0:
   result.text = @"Never";
   break;
  ........
  default:
  break;
 }
 }

 @end

and my MainView.h

 #import <UIKit/UIKit.h>
 #import <Foundation/Foundation.h>

 @interface MainView : UIView <UIAccelerometerDelegate> {
     IBOutlet UILabel *result;
  IBOutlet UILabel *shook;
 }

 - (IBAction)yesNo;
 - (void)motionEnded;

 @end     

Obviously there’s an error in there, I know that much, but where?!

Answer 1

It looks like you need to read the documentation in more depth to get to the bottom of this. Specifically the iOS Event Handling Guide.

From that document there are a few things which I would suggest you try:

1. Override canBecomeFirstResponder: and return YES (as per Listing 4-1).
2. Override viewDidAppear:animated: to become the first responder (as per Listing 4-1).
3. Override both motionBegan:withEvent: and motionCancelled:withEvent: as they do this in the example which may be because the framework is testing your view controller class to see if it responds to these selectors (as per Listing 4-2).

Look at the UIResponder Class Reference (from which UIViewController inherits) for more detail on the methods you are overriding.

As someone who came from a Microsoft / VB / .NET and Android / Java background to Cocoa / Objective-C programming I would strongly suggest you invest the time in reading the documentation. Initially the Apple documents seem impenetrable but they’re actually pretty good!

I hope that helps.