[iPhone] Pickers

1. Introduction
   Picker can be configured to display one dail or many. By defults, pickers display lists of text, but they can also be made to display images.
   
2. Types of Pickers
   
• UIDatePicker
• UIPickerView
3. Delegates & Datasource
   (The controller view containing date piciker need not conform to UIPickerViewDelegate and UIPickerViewDataSource)
   • UIPickerViewDelegate
   • Set the visible data of current row
     pickerView:titleForRow:forComponent:
     
   • ...
     
   • UIPickerViewDataSource
   • Set component count (Column count)
     numberOfComponentsInPickerView:
     
   • Set the count of rows of current component
     pickerView:numberOfRowsInComponent:
     
4. Dependent Component
   The data in some components depends on other component. For example, picker view contains 2 components, the first component is used to display proviences name, and the second component is used to display cities under the selected provience.
   
   1. Use NSDictionary to hold data
      #define COMPONENT_PROVIENCE = 0;
      #defien COMPONENT_CITY = 1;
      
      NSDictionary *pProvienceCity;
      NSArray *pProviences;
      NSArray *pCities;
      UIPickerView *pPickerView;
      
   2. Override pickerView:didSelectRow:inComponent:, then set the correct data array, finally, call reloadComponent: to reset
      - (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component
      {
          if (COMPONENT_PROVIENCE == component)
          {
              NSString *pProvience = [pProviences objectAtIndex:row]:
              self.pCities = [pProvienceCity objectForKey:pProvience];
              [pPickerView selectRow:0 inComponent:COMPONENT_CITY animated:YES];
              [pPickerView reloadComponent:COMPONENT_CITY];
          }
      }
      
   3. ....
      
5. Sample Code
1. Return data in selected row
   NSArray *pDrrayData;
   IBOutlet UIPcikerView *pPickerView;
   ...
   //Get the selected data in the first column, if you want to get //data in the third column, just replace 0 with 2
   NSInteger row = [pPickerView selectedRowInComponent:0];
   NSString *pData = pDrrayData[row];
2. Set data to picker
   Suppose defined following fields:
   #define COMPONENT_NAME = 0;
   #defien COMPONENT_NUM = 1;
   
   NSArray *pDataName;
   NSArray *pDataNum;
   IBOutlet *pPickerView;
   
   
   - (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component
   {
       if (COMPONENT_NAME == component)
       {
           return [pDataName objectAtIndex:row];
       }
       else
       {
           return [pDataNum objectAtIndex:row];
       }
   }
   
3. ...
   
6. ...

Reference

1. Beginning iPhone Development: Exploring the iPhone SDK
   Chapter: Application Settings and User Defaults
   Page: P139~183