@protocol UIPickerViewDataSource<NSObject>
@required
// returns the number of 'columns' to displ 返回piker的列数
- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView;
// returns the # of rows in each component.. 返回每列的行数
- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component;
@end
@protocol UIPickerViewDelegate<NSObject>
@optional
// returns width of column and height of row for each component. 设置每列的宽
- (CGFloat)pickerView:(UIPickerView *)pickerView widthForComponent:(NSInteger)component;
//设置每列的高
- (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
//设置每列的标题
- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component;
//设置自定义空件的宽和高
- (UIView *)pickerView:(UIPickerView *)pickerView viewForRow:(NSInteger)row forComponent:(NSInteger)component reusingView:(UIView *)view;
//选择时触发该时间
- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component;
@end
