UIAlertView and UIActionSheet

iOS 7 screenshots:

iOS 6 screenshots:

The app pauses for three seconds with a white screen and white status bar (black text on top of the status bar). Then it displays a UIAlertView with four buttons. If you press Ignore, it will wait for three more seconds and then display a UIActionSheet with five butons. If you press Call Premier Khrushchev, it will launch the Safari app and go to the Wikipedia article for Nikita Khrushchev. See the novel Fail-Safe, the film (Henry Fonda, Walter Matthau), and the video (George Clooney, Harvey Keitel).

A UIAlertView pops in out of nowhere. A UIActionSheet slides up from the bottom of a UIView. See Alert Views and Action Sheets in the Human Interface Guidelines.

A UIAlertView has a delegate that adopts the protocol UIAlertViewDelegate. A UIActionSheet has a delegate that adopts the UIActionSheetDelegate protocol. Our ViewController plays the rôle of both delegates.

Source code in Alert.zip

main.m
Class AlertAppDelegate
Class ViewController calls the showAlert: and showActionSheet: methods of the View.
Class View
Alert-Info.plist: in older versions of iOS, the information property list file had to contain the key CFBundleURLTypes.

Enumerations

A list of enumerations is a series of variables that hold consecutively numbered integers starting at zero by default. See the two lists at the top of ViewController.m.

Formatted for a mobile device

The URL
http://en.m.wikipedia.org/wiki/Nikita_Khrushchev
is formatted for a browser on a mobile device. The URL
http://en.wikipedia.org/wiki/Nikita_Khrushchev
is formatted for a browser on a desktop computer. Both URLs have one underscore.

Curly braces in a case

I had to write {curly braces} around the case actionKhrushchev: of the switch statement in the actionSheet:clickedButtonAtIndex: method of class ViewController because I declared variables in this case.

Launch another app

If the user presses the “Call Premier Khrushchev” button of the UIActionSheet, the applicationWillResignActive: and applicationDidEnterBackground: methods of the application delegate will be called, in that order. Then another application (Safari) will be launched. See the case actionkhrushchev: in the switch statement in the actionSheet:clickedButtonAtIndex: method in class ViewController.

When we press the Home button to stop Safari and resume this app, the applicationWillEnterForeground: and applicationDidBecomeActive: methods of the application delegate will be called, in that order.

The URL scheme

The URL can begin with one of the following schemes. Only http: worked on my iPhone Simulator. See Communicating with Other Apps. Does IHasApp tell you what schemes are accepted by the apps on your iPhone? iTunes Linkmaker.

http:
https:
tel:
mailto:

Things to try

Change the URL to @"http://maps.google.com/maps?q=Moscow"

Instead of scheduledTimerWithTimeInterval:target:selector:userInfo:repeats:, would it be easier to call the performSelector:withObject:afterDelay: we saw here?

If anything goes wrong with the recording and playback in Segmented, display a UIAlertView.

Let another app launch this app.

Any URL starting with http: will cause openURL: to launch Safari. Let’s make any URL starting with alert: launch our Alert app. See Registering Custom URL Schemes.

Edit the Alert-Info.plist file in the Supporting Files folder in XCode’s Project Navigator. Add a new key whose name is CFBundleURLTypes and whose value is an array of dictionaries that announces that another app can launch this one with any URL starting with alert:. The Alert-Info.plist file will contain the following lines. You can see them with TextEdit.app, or by control-clicking on Alert-Info.plist in the Project Navigator and selecting
Open As → Soure Code. When you are done editing, remove the app from the simulator and run it again.
```
	<key>CFBundleURLTypes</key>
	<array>
		<dict>
			<key>CFBundleURLName</key>
			<string>edu.nyu.scps.Alert</string>
			<key>CFBundleURLSchemes</key>
			<array>
				<string>alert</string>
                        </array>
                </dict>
        </array>
```

Create a second app. Insert the following code into the application:didFinishLaunchingWithOptions: method of the application delegate of the second app immediately before the return YES;. It uses the application argument passed to application:didFinishLaunchingWithOptions:.
```
	NSURL *url = [NSURL URLWithString: @"alert:"];

	if (![application canOpenURL: url]) {
		NSLog(@"can't open URL \"%@\", url);
		return YES;
	}

	NSLog(@"[application openURL: \"%@\"] == %d", url, [application openURL: url]);
```

Build and Run the second app.

The second app can include information in the URL after the colon. For example, the second app can create the URL by saying
```
	NSURL *url = [NSURL URLWithString: @"alert:hello"];
```
To receive this information, insert these statements into the application:didFinishLaunchingWithOptions: method of the Alert app.
```
	NSURL *url =
		[launchOptions objectForKey: UIApplicationLaunchOptionsURLKey];
	NSString *s = url == nil ? @"" : [url description];
```
If the Alert app was launched by a second app, the string s in the Alert app will now be the URL that the second app used (in this case @"alert:hello"), including the information after the colon. If the Alert app was launched by a finger tapping on the Alert app’s icon, the string s in the Alert app will be the empty string @"". Launch the Alert app by pressing the Xcode Run button before you launch the Alert app by running the second app.