UIPickerView 编程示例？

如何在不使用 Interface Builder 的情况下以编程方式在视图中设置 UIPickerView？还难以理解如何使用 UIPickerView 的委托部分。

以编程方式添加 UIPickerView：

- (void)pickerView:(UIPickerView *)pV didSelectRow:(NSInteger)row inComponent:(NSInteger)component
{
    if(component == 1)
        selectedRowPicker1 = row;
    else if(component == 2)
        selectedRowPicker2 = row;
    else
        selectedRowPicker3 = row;
}

- (NSInteger)numberOfComponentsInPickerView:(UIPickerView *)pickerView
{
    return 3;
}

- (NSInteger)pickerView:(UIPickerView *)pickerView numberOfRowsInComponent:(NSInteger)component
{ 
    if(component == 1)
        return [list1 count];
    else if(component == 2)
        return [list2 count];
    else
        return [list3 count];
}

- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component
{
    if(component == 1)
        val1 = [list1 objectAtIndex:row];
    else if(component == 2)
        val2 = [list2 objectAtIndex:row];
    else
        val3 = [list3 objectAtIndex:row];

    return strTemp;
}