UIPickerView无法解释的警告

Question

I implemented a simple UIPickerView in my app and I keep getting warnings that I can't explain about incomplete implementation and "method in protocol not completed". I went through a bunch of examples and could not figure out what am I missing.

Here is my code:

.h

@interface ViewTestViewController : UIViewController <UITableViewDelegate, UITableViewDataSource, UIPageViewControllerDataSource, UIPageViewControllerDataSource> {

 UIPickerView *pickerView;
NSMutableArray *pickerList;

....

}
@property (nonatomic, retain) IBOutlet UIPickerView *pickerView;
@property (nonatomic, retain) NSMutableArray *pickerList;


@end

.m

- (void)viewDidLoad
{
[super viewDidLoad];

 …

//PICKER AREA
pickerList = [[NSMutableArray alloc] init];
[pickerList addObject:@"aaa"];
[pickerList addObject:@"bbb"];

CGRect pickerFrame = CGRectMake(0, 200, 0, 0);
pickerView = [[UIPickerView alloc] initWithFrame:pickerFrame];
pickerView.showsSelectionIndicator = YES;    

}

-(IBAction)showPicker:(id)sender {

 [self.view addSubview:pickerView];

}

-(NSInteger)numberOfComponentsInPickerView:(UIPickerView *)thePickerView
{
return 1;
}

-(NSInteger)pickerView:(UIPickerView *)thePickerView numberOfRowsInComponent:(NSInteger)component
 {
return [pickerList count];
}

-(NSString *)pickerView:(UIPickerView *)thePickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component
{
return [pickerList objectAtIndex:row];
}

-(void)pickerView:(UIPickerView *)thePickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component
{
NSLog(@"Selected item: %@ index of selected item: %i", [pickerList objectAtIndex:row], row);
}

- (CGFloat)pickerView:(UIPickerView *)pickerView rowHeightForComponent:(NSInteger)component
{

return 200;
}

Answer 1

You need to conform to the UIPickerViewDelegate and UIPickerViewDataSource in your .h like you do for UITableViewDelegate, UITableViewDataSource etc (you're currently not)

@interface ViewTestViewController : UIViewController <UIPickerViewDataSource, UIPickerViewDelegate, UITableViewDelegate, UITableViewDataSource, UIPageViewControllerDataSource, UIPageViewControllerDataSource> {

Also, make sure you are setting self as the picker view delegate and data source when you create it:

//PICKER AREA
pickerList = [[NSMutableArray alloc] init];
[pickerList addObject:@"aaa"];
[pickerList addObject:@"bbb"];

CGRect pickerFrame = CGRectMake(0, 200, 0, 0);
pickerView = [[UIPickerView alloc] initWithFrame:pickerFrame];
pickerView.showsSelectionIndicator = YES; 
pickerView.dataSource = self;
pickerView.delegate = self;

Answer 2

In your .h file you declare yourself as conforming to these protocols:

<UITableViewDelegate, UITableViewDataSource, UIPageViewControllerDataSource, UIPageViewControllerDataSource>

Each of those protocols involves some methods you have to implement (see the documentation on each one for the details). If you don't implement all the required methods, you will get this warning.