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Swift - 选择框（UIPickerView）的用法

1，选择框可以让用户以滑动的方式选择值。示例如下：

import UIKit
 
class ViewController:UIViewController, UIPickerViewDelegate, UIPickerViewDataSource{
     
    var pickerView:UIPickerView!
     
    override func viewDidLoad() {
        super.viewDidLoad()
        pickerView=UIPickerView()
        //将dataSource设置成自己
        pickerView.dataSource=self
        //将delegate设置成自己
        pickerView.delegate=self
        //设置选择框的默认值
        pickerView.selectRow(1,inComponent:0,animated:true)
        pickerView.selectRow(2,inComponent:1,animated:true)
        pickerView.selectRow(3,inComponent:2,animated:true)
        self.view.addSubview(pickerView)
         
        //建立一个按钮，触摸按钮时获得选择框被选择的索引
        var button=UIButton(frame:CGRectMake(0,0,100,30))
        button.center=self.view.center
        button.backgroundColor=UIColor.blueColor()
        button.setTitle("获取信息",forState:.Normal)
        button.addTarget(self, action:"getPickerViewValue",
            forControlEvents: UIControlEvents.TouchUpInside)
        self.view.addSubview(button)
    }
    //设置选择框的列数为3列,继承于UIPickerViewDataSource协议
    func numberOfComponentsInPickerView( pickerView: UIPickerView) -> Int{
        return 3
    }
     
    //设置选择框的行数为9行，继承于UIPickerViewDataSource协议
    func pickerView(pickerView: UIPickerView,numberOfRowsInComponent component: Int) -> Int{
        return 9
    }
     
    //设置选择框各选项的内容，继承于UIPickerViewDelegate协议
    func pickerView(pickerView:UIPickerView!,titleForRow row: Int,forComponent component: Int)
        -> String!{
        return String(row)+"-"+String(component)
    }
     
    //触摸按钮时，获得被选中的索引
    func getPickerViewValue(){
        var alertView=UIAlertView();
        alertView.title="被选中的索引为"
        alertView.message=String(pickerView.selectedRowInComponent(0))+"-"+String(pickerView!.selectedRowInComponent(1))+"-"+String(pickerView.selectedRowInComponent(2))
        alertView.addButtonWithTitle("OK")
        alertView.show()
    }
}

2，调整选择框的尺寸
UIPickerView用frame和center两个属性设置整个选择框的大小和位置。
如果要调整内部列的宽度，需要实现UIPickerViewDelegate协议类中pickerView:widthForComponent方法设置
如果要调整内部行高，则需要实习上述协议类中pickerView:rowHeightForComponent方法设置

//设置列宽
func pickerView(pickerView: UIPickerView！,widthForComponent component: Int) -> CGFloat{
    if(00 == component){
        //第一列变宽
        return 100
    }else{
        //第二、三列变窄
        return 30
    }
}
 
//设置行高
func pickerView(pickerView: UIPickerView！,rowHeightForComponent component: Int) -> CGFloat{
    return 50
}

3，将图片作为选择框选项
选择框选项的内容，除了可以使字符串类型的，还可以是任意UIView类型的元素。比如我们将选项内容设置为图片：

func pickerView(pickerView:UIPickerView!,viewForRow row: Int,forComponent component: Int,
 reusingView view:UIView!) -> UIView!{
    var image = UIImage(named:"icon_"+String(row))
    var imageView = UIImageView()
    imageView.image = image
    return imageView
}

4，检测响应选项的选择状态

func pickerView(pickerView: UIPickerView！,didSelectRow row: Int, inComponent component: Int){
    //将在滑动停止后触发，并打印出选中列和行索引
    println(component)
    println(row)
}