新风作浪博客学习(八)代码实现UIPickerView .

先说一下当个组件选取器，我们创建一个数组NSAray来保存选取器中的内容；选取器本身不会储存任何数据，，它通过调用数据源和委托方法来显示数据；但是对于大量数据的数据源，数组并不合适，我们可以做一个静态列表如plist文件或者URL载入，和后面将讲在文件中获取数据，还以多个选取器的之间的关联如何实现；先说下简单的单个选取器:

先把效果图贴出来

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1.新建工程名为PickerViewDemo ， File->New->Project ->single View Application -> next
[img]

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2.在视图上添加选取器

pickerView = [[UIPickerView alloc] initWithFrame:CGRectMake(0, 0, 320, 216)];
//    指定Delegate
    pickerView.delegate=self;
//    显示选中框
    pickerView.showsSelectionIndicator=YES;
    [self.view addSubview:pickerView];

以上可以在视图显示一个选取器，但是内容空白，pickerView.showsSelectionIndicator=YES;是这只当前选取器所选中的内容：

选取器上显示数据，必须依赖两个协议，UIPickerViewDelegate和UIPickerViewDataSource，把他们添加到ViewController.h文件中

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController<UIPickerViewDelegate,UIPickerViewDataSource>
{

    UIPickerView *pickerView;
    NSArray *pickerData;

}

@end

3.然后在.m文件的ViewDidLoad中初始化界面
[img]- (void)viewDidLoad
{
    [super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
   
    pickerView = [[UIPickerView alloc] initWithFrame:CGRectMake(0, 0, 320, 216)];
//    指定Delegate
    pickerView.delegate=self;
//    显示选中框
    pickerView.showsSelectionIndicator=YES;
    [self.view addSubview:pickerView];
   
    NSArray *dataArray = [[NSArray alloc]initWithObjects:@"许嵩",@"周杰伦",@"梁静茹",@"许飞",@"凤凰传奇",@"阿杜",@"方大同",@"林俊杰",@"胡夏",@"邱永传", nil];
   
    pickerData=dataArray;
   
//     添加按钮  
    CGRect frame = CGRectMake(120, 250, 80, 40);
    UIButton *selectButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    selectButton.frame=frame;
    [selectButton setTitle:@"SELECT" forState:UIControlStateNormal];
   
    [selectButton addTarget:self action:@selector(buttonPressed:) forControlEvents:UIControlEventTouchUpInside];
   
    [self.view addSubview:selectButton];
   
}[/img]






4.实现UIPickerView的代理方法，将数据显示在选取器上所需要几个方法

#pragma mark -
#pragma mark Picker Date Source Methods

//返回显示的列数
-(NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView
{
    return 1;
}
//返回当前列显示的行数
-(NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component
{
    return [pickerData count];
}

#pragma mark Picker Delegate Methods

//返回当前行的内容,此处是将数组中数值添加到滚动的那个显示栏上
-(NSString*)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component
{
    return [pickerData objectAtIndex:row];
}

前两个是数据源的代理方法，一个是返回列，有几个选取器就返回几，第二个是设置选取器有多少行，因为就这一个选取器，所以直接返回行数，即数组元素个数多少；第三个代理方法是将数组元素添加到了选取器上面显示；



UIPickerViewDelegate中的实例方法


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

作用: 当用户选择某个row时,picker view调用此函数

参数: pickerView representing the picker view request the data

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

作用:由picker view调用,当其在绘制row内容,需要row的高度时

-(NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger) component

作用: 当picker view需要给指定的component.row指定title时,调用此函数

-(UIView *)pickerView: (UIPickerView *)pickerView view ForRow:(NSInteger) row forComponent:(NSInteger) component reusingView:(UIView *) view

作用: 当picker view需要给指定的component.row指定view时,调用此函数.返回值为用作row内容的view

参数: view参数, a view object that was previously used for this rows, but is now hidden and cached by the picker view

- （CGFloat)pickerView: (UIPickerView *)pickerView widthForComponent:(NSInteger) component

作用:当picker view 需要row的宽度时,调用此函数




UIPickerViewDataSource中的实例方法：
按照官方文档的说法,UIPickerViewDataSource这个协议仅有的功能就是提供picker view中component的个数和各个component中的row的个数,虽然名为datasource,但是它工作于MVC的C中

本协议仅有两个实例方法,均需要实现

-(NSInteger) numberOfComponentsInPickerView:(UIPickerView *)pickerView

作用:返回pickerView应该有几个component

-(NSInteger) pickerView:(UIPickerView *) pickerView numberOfRowsInComponent:(NSInteger) component

作用:返回指定component应该有几个row





5.关于按钮响应事件，关于按钮的形成和添加响应事件不再提，前面都有，

-(void) buttonPressed:(id)sender
{
     NSInteger row =[pickerView selectedRowInComponent:0];
     NSString *selected = [pickerData objectAtIndex:row];
     NSString *message = [[NSString alloc] initWithFormat:@"你选择的是:%@",selected];
    
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"提示" 
                                                    message:message
                                                   delegate:self
                                          cancelButtonTitle:@"OK"
                                          otherButtonTitles: nil];
    [alert show];
    
}

[pickerViewselectedRowInComponent:0];方法返回当前被选中的索引序号，这是UIPickerView的实例方法，在官方文档中






UIPickerView还有其他实例方法

- (NSInteger) numberOfRowsInComponent:(NSInteger)component

参数为component的序号(从左到右,以0起始),返回指定的component中row的个数

-(void) reloadAllComponents

调用此方法使得PickerView向delegate: Query for new data for all components

-(void) reloadComponent: (NSInteger) component

参数为需更新的component的序号,调用此方法使得PickerView向其delegate: Query for new data

-(CGSize) rowSizeForComponent: (NSInteger) component

参数为component的序号,返回值为the size of rows in the given components, picker view 通过调用委托方法中的pickerView:widthForComponent:和pickerView:rowHeightForComponent:获得返回值

-(NSInteger) selectedRowInComponent: (NSInteger) component

参数为component的序号,返回被选中row的序号,若无row被选中,则返回-1

-(void) selectRow: (NSInteger)row inComponent: (NSInteger)component animated: (BOOL)animated

作用:在代码指定要选择的某component的某row

参数:row序号,component序号,BOOL值(若为YES,转动spin到你选择的新值,若为NO,直接显示你选择的值)

-(UIView *) viewForRow: (NSInteger)row forComponent: (NSInteger)component

参数:row序号,component序号,返回由委托方法pickerView:viewForRow:forComponentreusingView:指定的view.如果委托对象并没有实现这个方法,或者说这个view并不是可见的,则返回nil