（UIPickerView）選擇器的使用--互相依賴的多列選擇器

首先建立工程，然後再stroyboard拖入UIPicker，為在程式中通路該控件，需要将該控件綁定到picker IBOutlet屬性

然後實作兩個協定，這兩個協定是必須存在的。代碼如下

#import "ViewController.h"

@interface ViewController ()<UIPickerViewDataSource,UIPickerViewDelegate>


@property (strong, nonatomic) IBOutlet UIPickerView *picker;

@end

@implementation ViewController
{
    NSDictionary *books;
    NSArray *authors;
    //selectedAuthor儲存目前選中的作者
    NSString *selectAuthor;
}
- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    //建立并初始化NSDictionary對象
    books = [NSDictionary dictionaryWithObjectsAndKeys:
             [NSArray arrayWithObjects:@"飛鳥集",@"祭壇急了", nil],@"泰戈爾",
             [NSArray arrayWithObjects:@"醒世恒言",@"喻世明言",@"警世通言", nil],@"馮夢龍",
             [NSArray arrayWithObjects:@"ios講義",@"andros講義",@"java講義",@"xml講義", nil],@"李剛",nil];
    //使用author 儲存books所有key所組成的NSArray排序後的結果
    authors = [[books allKeys] sortedArrayUsingSelector:@selector(compare:)];
    //使用預設選中的作者authors中的第一個元素
    selectAuthor = [authors objectAtIndex:0];
    
    self.picker.delegate = self;
    self.picker.dataSource = self;
    
}
//該方法傳回控件該控件包含多少列
-(NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView
{
    return 2;
}
//該方法傳回值決定該控件的制定列包含多少個清單項
-(NSInteger)pickerView:(UIPickerView *)pickerView                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              numberOfRowsInComponent:(NSInteger)component
{
    if (component == 0) {
        return authors.count;
    }
    return [[books objectForKey:selectAuthor] count];
}
-(NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component
{
    //若果是第一列，則傳回authors中的元素的個數
    //即authors有多少個元素，那麼第一列就包含多少個清單項
    if (component == 0) {
        return [authors objectAtIndex:row];
    }
    //否則其他列傳回的個數是books中的鍵值對中值對應的數組地元素的個數
    return [[books objectForKey:selectAuthor] objectAtIndex:row];
}
-(CGFloat)pickerView:(UIPickerView *)pickerView widthForComponent:(NSInteger)component
{
     //如果是第一列，則寬度是90
    if (component == 0  ) {
        return 90;
    }
    return 210;
}
-(void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component
{
   
    if (component == 0) {
        //改變選中的作者
        selectAuthor = [authors objectAtIndex:row];
    }
    //控制重寫加載第二個清單，根據選中的作者來加載第二個清單項
    [self.picker reloadComponent:1];
}

@end
           

運用下面該方法可以任意定制自己的的選擇器視圖

-(UIView *)pickerView:(UIPickerView *)pickerView viewForRow:(NSInteger)row forComponent:(NSInteger)component reusingView:(UIView *)view
{
    view = [[UIImageView alloc]initWithImage:[UIImage imageNamed:@"引導頁二640-1136"]];
    return view;
}
           

如圖所示