picker控件详解与使用，（实现省市的二级联动）

第一步：新建一个单视图（single view）的工程，

命名为pickerTest，不要勾选下面两个选项，第一个是新版本里面的，第二个是单元测试，现在用不着。

点击next ->creat之后，打开工具栏：

在下面的控件工具栏中往视图上拖放一个Picker View控件，一个UIButton控件，一个UILable控件，（所有在前端可以看得见的控件都继承自UIView）

修改UIButton的title属性，设置为click 然后点击分栏按钮，为控件连线（这种方式相对于手动去写，要快速很多）。

依次为UILable 和 Picker View 控件添加插座变量，并且为UIButton添加Action

右击picker控件，将 Datesource和delegate连线至File's Owner, 设置它的数据源和代理。

在 cidpViewController.h文件中添加几个变量和遵循 UIPickerViewDelegate 协议，这样就可以用UIPickerViewDelegate里面的几个方法了。

@interface cidpViewController : UIViewController<UIPickerViewDelegate>

#import <UIKit/UIKit.h>

@interface cidpViewController : UIViewController<UIPickerViewDelegate> {
    UILabel *lblTitle;
    UIPickerView *picker;
    NSString* strProvince;
    NSString* strCity;
    NSMutableArray* aProvince;
    NSMutableArray* aCity;
    NSArray* tempArray;
}
@property (strong, nonatomic) IBOutlet UIPickerView *picker;

@property (strong, nonatomic) IBOutlet UILabel *lblTitle;
- (IBAction)btnClick:(id)sender;

@end

#import "cidpViewController.h"

@implementation cidpViewController

@synthesize picker;
@synthesize lblTitle;

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Release any cached data, images, etc that aren't in use.
}

#pragma mark - View lifecycle

- (void)viewDidLoad
{
    [super viewDidLoad];
    //初始哈5个省份
    aProvince = [[NSMutableArray alloc] initWithObjects:@"北京",@"甘肃",@"山西",@"湖北",@"广州", nil];
    //初始化5个数组 ，分别初始化为5个省的城市
    NSArray* array1 = [NSArray arrayWithObjects:@"海淀",@"昌平",@"朝阳",@"西城",@"丰台", nil];
    NSArray* array2 = [NSArray arrayWithObjects:@"兰州",@"白银",@"张掖",@"陇西",@"天水", nil];
    NSArray* array3 = [NSArray arrayWithObjects:@"太原",@"大同",@"运城",@"晋城",@"五台山", nil];
    NSArray* array4 = [NSArray arrayWithObjects:@"武汉",@"荆州",@"襄阳",@"赣州", nil];
    NSArray* array5 = [NSArray arrayWithObjects:@"广州",@"佛山",@"尖沙咀",@"中山", nil];
    aCity = [[NSMutableArray alloc] initWithObjects:array1,array2,array3,array4,array5, nil];
    //tempArray 用来初始化第二个 ，并且引用一次，避免提前释放，内存出错
    tempArray = [array1 retain];
    // 用来第一次显示UIlable，负责的话就会显示 null，null 
    strProvince = [aProvince objectAtIndex:0];
    strCity = [tempArray objectAtIndex:0];
    [aProvince release];
    [aCity release];
    
}
-(NSInteger)numberOfComponentsInPickerView:(UIPickerView*)pickerView{
    //返回2 表示将有两个component（滚轮）
    return 2;
}

-(NSInteger)pickerView:(UIPickerView*)pivkerView numberOfRowsInComponent:(NSInteger)component{
    if(component == 0){
        // 返回省份数组的长度
        return [aProvince count];
    }else{
        //返回省份对应城市数组的长度。
        [tempArray count];
}

- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component{
        if(component == 0){
            //返回对应row 的数组元素。
            return [aProvince objectAtIndex:row];
        }else{
            
            return [tempArray objectAtIndex:row];
        }
}

- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component{
    if(component == 0){
        //返回省份对应的城市数组，
        tempArray = [aCity objectAtIndex:row]
        [picker selectRow:0 inComponent:1 animated:YES];
        [picker reloadComponent:1];
        strProvience = [aProvince objectAtIndex:row];
        strCity = [tempArray objectAtIndex:0];
    }else{
        //城市滚轮滚动时，strCity也随着改变。
       strCity =  [tempArray objectAtIndex:0];
    }
    lblTitle.text = [[NSString alloc] initWithFormat:@"%@,%@",strProvince,strCity,nil];
}
    
- (void)viewDidUnload
{
    [self setLblTitle:nil];
    [self setPicker:nil];
    [super viewDidUnload];
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
}

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
}

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
}

- (void)viewDidDisappear:(BOOL)animated
{
    [super viewDidDisappear:animated];
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

- (IBAction)btnClick:(id)sender {
    lblTitle.text = [[NSString alloc] initWithFormat:@"%@,%@",strProvince,strCity,nil];
}
-(void)dealloc{
    [aProvince release];
    [aCity release];
    [lblTitle release];
    [strCity release];
    [strProvince release];
    [picker release];
    [super  dealloc];
    
}
@end

@protocol UIPickerViewDataSource<NSObject>
@required

// returns the number of 'columns' to display.
- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView;

// returns the # of rows in each component..
- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component;
@end

UIPickerViewDelegate协议中的五个方法，非必须实现，

@protocol UIPickerViewDelegate<NSObject>
@optional

// returns width of column and height of row for each component. 
- (CGFloat)pickerView:(UIPickerView *)pickerView widthForComponent:(NSInteger)component;
- (CGFloat)pickerView:(UIPickerView *)pickerView rowHeightForComponent:(NSInteger)component;

// these methods return either a plain UIString, or a view (e.g UILabel) to display the row for the component.
// for the view versions, we cache any hidden and thus unused views and pass them back for reuse. 
// If you return back a different object, the old one will be released. the view will be centered in the row rect  
- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component;
- (UIView *)pickerView:(UIPickerView *)pickerView viewForRow:(NSInteger)row forComponent:(NSInteger)component reusingView:(UIView *)view;

- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component;

@end