Controls Part Two: Using Pickers and Using the Camera in Objective-C

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Controls Part Two: Using Pickers and Using the Camera
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Content The pickerView:titleForRow:forComponent: and pickerView:viewForRow:for Component: methods provide a component s title or view The title or the view is what is displayed as the rows in a picker You must implement one of the two methods If using a string, implement the pickerView:titleForRow:forComponent: method; if using a view, implement the pickerView:viewForRow:forComponent: method Each method s signature follows
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- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow: (NSInteger) row forComponent: (NSInteger) component - (UIView *)pickerView:(UIPickerView *)pickerView viewForRow:(NSInteger) row forComponent:(NSInteger)component reusingView:(UIView *)view
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Selecting The UIPickerView calls the pickerView:didSelectRow:inComponent: method when a user selects a component s row It takes the component s index number and the row s index number as parameters, so you can determine the component selected and the component s row The method s signature follows
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- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component
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UIPickerViewDatasource
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A UIPickerViewDatasource handles a UIPickerView s data It contains two methods you should define when adopting this protocol: the numberOfComponentsInPickerView: and pickerView:numberOfRowsInComponent: methods The numberOfComponentsInPickerView: method returns how many components, or columns, a picker must display
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- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent: (NSInteger) component
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The pickerView:numberOfRowsInComponent: method returns a component s row count
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- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent: (NSInteger) component
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Try This
Using a Picker
1 Create a new View-based Application named APicker 2 Open APickerViewControllerxib in Interface Builder 3 Drag a picker view from the library to the canvas Right-click and notice that the control
doesn t have the choices a UIDatePicker has (Figure 13-10)
(continued)
iPhone SDK Programming: A Beginner s Guide
Figure 13-10
A UIPickerView has less outlets and actions than a UIDatePicker
4 Add a button to the canvas 5 Save and exit Interface Builder 6 Create a new NSObject named MyPickerDelegate and change it to adopt the
UIPickerViewDelegate and UIPickerViewDataSource protocols Have MyPickerDelegate implement the needed methods (Listings 13-7 and 13-8)
7 Open APickerViewController and add IBOutlets for UIPickerView and MyPickerDelegate
(Listing 13-9) Add an IBAction called changeColor
8 Implement the changeColor action (Listing 13-10) 9 Save and build Open APickerViewControllerxib in Interface Builder 10 Connect File s Owner changeColor action to the button s Touch Up Inside event 11 Connect File s Owner myPicker outlet to the UIPickerView 12 Drag an object from the library to the document window Change the object s type to
MyPickerDelegate
13 Connect the File s Owner myPickerDelegate outlet to the object just added 14 Connect the UIPickerView s dataSource and delegate outlets to the newly added object
13:
Controls Part Two: Using Pickers and Using the Camera
Figure 13-11
Running the application in iPhone Simulator
15 Save and exit Interface Builder 16 Click Build And Go to run the application in iPhone Simulator Upon pushing the button,
the debugger console logs the picker s chosen color (Figure 13-11 and Listing 13-11) Listing 13-7 MyPickerDelegateh
#import <Foundation/Foundationh> @interface MyPickerDelegate : NSObject <UIPickerViewDelegate, UIPickerViewDataSource> { NSArray * myData; } @property (nonatomic, retain) NSArray * myData; @end
(continued)
iPhone SDK Programming: A Beginner s Guide
Listing 13-8
MyPickerDelegatem
#import "MyPickerDelegateh" @implementation MyPickerDelegate @synthesize myData; - (id) init { if([super init] == nil) return nil; myData = [[NSArray alloc] initWithObjects:@"Red",@"Yellow",@"Green",@"Blue", @"Purple", @"Orange", @"Black", @"Gray", @"Tan", @"Pink", @"Coral", nil]; return self; } - (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component { NSLog(@"picked row: %i, component: %i", row, component); NSLog(@"the value: %@", [selfmyData objectAtIndex:row]); } - (NSInteger) numberOfComponentsInPickerView: (UIPickerView *) pickerView { return 1; } - (NSInteger) pickerView: (UIPickerView *) pickerView numberOfRowsInComponent: (NSInteger) component { return [selfmyData count]; } - (NSString *) pickerView: (UIPickerView *) pickerView titleForRow: (NSInteger) row forComponent: (NSInteger) component { return [selfmyData objectAtIndex:row]; } - (void)dealloc { [myData release]; [super dealloc]; } @end
Listing 13-9
APickerViewControllerh
#import <UIKit/UIKith> #import "MyPickerDelegateh" @interface APickerViewController : UIViewController { IBOutlet UIPickerView * myPicker; IBOutlet MyPickerDelegate * myPickerDelegate; }
13:
Controls Part Two: Using Pickers and Using the Camera
@property (nonatomic, retain) IBOutlet UIPickerView * myPicker; @property (nonatomic, retain) IBOutlet MyPickerDelegate * myPickerDelegate; - (IBAction) changeColor: (id) sender; @end
Listing 13-10
APickerViewControllerm
#import "APickerViewControllerh" @implementation APickerViewController @synthesize myPicker; @synthesize myPickerDelegate; - (IBAction) changeColor: (id) sender { NSLog(@"the color is: %@", (NSString *)[myPickerDelegatemyData objectAtIndex: [myPicker selectedRowInComponent:0]]); } - (void)dealloc { [myPickerDelegate release]; [myPicker release]; [super dealloc]; } @end
Listing 13-11
Debug console output from running APicker application
[Session started at 2009-02-06 22:57:09 -0500] 2009-02-06 22:57:13007 APicker[429:20b] picked row: 1, component: 0 2009-02-06 22:57:13008 APicker[429:20b] the value: Yellow 2009-02-06 22:57:14687 APicker[429:20b] picked row: 3, component: 0 2009-02-06 22:57:14687 APicker[429:20b] the value: Blue 2009-02-06 22:57:16540 APicker[429:20b] picked row: 8, component: 0 2009-02-06 22:57:16541 APicker[429:20b] the value: Tan 2009-02-06 22:57:17499 APicker[429:20b] the color is: Tan 2009-02-06 22:57:21215 APicker[429:20b] picked row: 10, component: 0 2009-02-06 22:57:21215 APicker[429:20b] the value: Coral 2009-02-06 22:57:22547 APicker[429:20b] the color is: Coral
A UIPickerView must have helper classes adopting the UIPickerViewDelegate and UIPickerViewDataSource protocols In this example, you had one class, MyPickerDelegate, adopt both protocols The delegate uses a simple NSArray to hold NSString objects Because the data is simple strings, the delegate implements the titleForRow method When a user selects a row, the didSelectRow method logs the row, component, and value to the debugger console
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