UI ：使用 UIPickerView 来选择数据

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController<UIPickerViewDataSource,UIPickerViewDelegate>

@property(nonatomic,strong)UIPickerView *myPicker;

@end

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    self.view.backgroundColor = [UIColor whiteColor];
    self.myPicker = [[UIPickerView alloc]init];
    self.myPicker.center = self.view.center;
    
    self.myPicker.delegate = self;//设置代理
    self.myPicker.showsSelectionIndicator = YES;
    [self.view addSubview:self.myPicker];
    //此时pickerView没有数据，效果不好.
    ///为选择器添加数据:首先给 picker view 指定一个 data source,然后确保 view controller 遵循相关的协议。UIPickerView 的 data source 实例必须遵循 UIPickerViewDataSource 协议。
}

//UIPickerViewDataSource @required协议方法的实现
-(NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView{
    //这个方法主要是用来为你的选择器添加组件的,如果你需要多个组件,你可以在这个里面进行添加.
    return 1;
}
-(NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component{
    //顾名思义,这个方法表示你的一个组件中有多少个选项。
    return 10;
}
//UIPickerViewDelegate 协议方法
-(NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component{
    NSString *result = nil;
    if ([pickerView isEqual:_myPicker]) {
        result = [NSString stringWithFormat:@"Row%ld",row+1];
    }
    return result;
}