Objective C - Convert string to double and double to string

Before we go on to part 3, let me stop to pause for an important part of the code and zoom in a little more. For in the code, we have done something important, converting double into a string, and string into a double.

Now i initially thought that a simple google search would return me the result but to my horror...it doesn't! Especially for the double to format to 2 dp and become a string.

So here goes...

double loanAmount = [tbxLoanAmount.text doubleValue];

Remember the above code? Its to the equivalent of double d = Convert.ToDouble(tbx.Text) in C#. Over here, we are calling the doubleValue method of the String (or rather NSString - NS = NextStep) class to convert the text box Text property into a double.

NSNumberFormatter *numberFormatter = [[NSNumberFormatter alloc] init];

[numberFormatter setNumberStyle:NSNumberFormatterDecimalStyle];

[numberFormatter setMaximumFractionDigits:2];

We now create the NumberFormatter object. Again its prefixxed with NS - NextStep. This object will format our 1.234566 into a nice 1.23 format. Of course you can format to percentages as well. There are also other formatters like date formatters.

NSNumberFormatter *numberFormatter = [[NSNumberFormatter alloc] init];

We create the NumberFormatter object here. In short, we are doing a NumberFormatter nf = new NumberFormatter() here. [NSNumberFormatter alloc] is for allocating memory to hold this object. init - initialization. You will see [[Object alloc] init] very frequently.

NSNumber *n1 = [NSNumber numberWithDouble:paymentAmt];

Next, convert the double into a NSNumber type with the above code. Again, in C#, it will be NSNumber n1 = NSNumber.numberWithDouble(payment); Yea, its a static method.

 NSString *paymentAmtString = [numberFormatter stringFromNumber:n1];

Finally, using the numberFormatter object, which takes in a NSNumber argument, we finally convert our double to a String. Which we can assign to a text box Text property as per below.

monthlyPayment.text = paymentAmtString;

So in summary, double -> NSNumber -> NSNumberFormatter -> NSString.

Unbelieveable right, the amount of work you need to convert a formatted double into a String.

Yea, still more unbelievable things to come.

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