picker view - units conversion

Question

I'm developing an application with a picker view that slide from the bottom (like an action sheet). I need to convert 3 units (litres, us gallons and imperial gallons). The value is taken from a text field but I don't know how to tell the compiler which was the unit to start from. (ie...the user insert the value in the the text field but if he changes the units (usg or ig), the value in the text field changes accordingly.

this is the array:

  NSMutableArray *weightArray = [[NSMutableArray alloc] initWithObjects:@"", @"Ltr",@"Usg",@"Ig",
                               nil];
self.weightPickerViewArray = weightArray;
[weightArray release];`

this is the picker:

- (void)pickerView:(UIPickerView *)thePickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component { 
if (row == 1) {
    labelVolume.text = [weightPickerViewArray objectAtIndex:row];

  //more code here....

}else if (row == 2){
    labelVolume.text = [weightPickerViewArray objectAtIndex:row];

    //more code here....
}else if (row == 3){
    labelVolume.text = [weightPickerViewArray objectAtIndex:row];

    //more code here....

} how can I tell the compiler which was the value before the selection?

Answer 1

Add a text indicating the units at the end of the string.

- (void)pickerView:(UIPickerView *)thePickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component { 
if (row == 1) {
    NSString *initalValue = labelVolume.text;
    // Do your calculations here based on unit
    NSString *updatedValue = urNewValue;
    labelVolume.text = updatedValue;

  //more code here....

}else if (row == 2){
NSString *initalValue = labelVolume.text;
    // Do your calculations here based on unit
    NSString *updatedValue = urNewValue;
    labelVolume.text = updatedValue;


    //more code here....
}else if (row == 3){
NSString *initalValue = labelVolume.text;
    // Do your calculations here based on unit
    NSString *updatedValue = urNewValue;
    labelVolume.text = updatedValue;


    //more code here....
}