UIPickerView(loading...)

1. pickerView 中 有几个部分

- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView;

2. 某个部分有几行

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

3. 每一部分每一行显示的文字

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

4. 拖动结束后对应的行和部分

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

5. 让 self.pickerView 去 选中 第i个部分currentRow行(有个缓慢动画的过程)

[self.pickerView selectRow:currentRow inComponent:i animated:YES];

6.拿到 i这个部分对应的行

NSInteger oldRow = [self.pickerView selectedRowInComponent:i];

7. pickerView 中的宽高

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

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

8.  刷新pickerView中 city这一部分

[self.pickerView reloadComponent:MSProvinceOrCityTypeCity];

9. 自定义pickerView的row时调用

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