Question

it is probably a very simple problem but I spent already a lot of time on it and just have given up…
I have a button and a textfield for speed calculations. I want the button label change once the button is pressed (km/h >> mph >> m/s >> km/h and so on) and speed recalculated. It sometimes works fine but very often it jumps to “else” statement even if the CurrentSpeedValue is @”km/h”. Could anyone help? Maybe it would be better to use switch-case method but how should it be stated?

- (IBAction)speedChange:(id)sender {
//CurrentSpeedUnit is saved to NSUserDefault in another action
    if (CurrentSpeedUnit == @"km/h") {
        [sender setTitle:@"mph" forState:UIControlStateNormal];
        CurrentSpeedUnit = @"mph";
        float speedToPrint = ([textSpeed.text floatValue]) / 1.609344;
        textSpeed.text = [[NSString alloc] initWithFormat:@"%.3f", speedToPrint];
    } else if (CurrentSpeedUnit == @"mph") {
        [sender setTitle:@"m/s" forState:UIControlStateNormal];
        CurrentSpeedUnit = @"m/s";
        float speedToPrint = ([textSpeed.text floatValue]) * 1.609344 / 3.6;
        textSpeed.text = [[NSString alloc] initWithFormat:@"%.3f", speedToPrint];
    } else {
        [sender setTitle:@"km/h" forState:UIControlStateNormal];
        CurrentSpeedUnit = @"km/h";
        float speedToPrint = ([textSpeed.text floatValue]) * 3.6;
        textSpeed.text = [[NSString alloc] initWithFormat:@"%.3f", speedToPrint];
    }
}

Answer 1

You should not compare strings like that (you compare pointers but not the contents). Use isEqualToString.

i.e.

if ([CurrentSpeedUnit isEqualToString:@"km/h"]) {
...

but not your

if (CurrentSpeedUnit == @"km/h") {

It may work sometimes, but just remember to avoid comparing strings with ==