Realtime Calculator - objective-c

Question

For a school assignment I have been told to make a calculator app, the same as the spotlight calculator. It works in realtime and has no buttons for things to begin.
So far this is my code. It is written in a text field with the event Editing Did End. Im pretty sure thats wrong but i can't find an alternative solution. Also i haven't gotten the realtime thing to work so i've kind of reverted to completing the following steps when pressed off the text field.
- (IBAction)Didend_Action:(id)sender {
NSString *list = [Sum_TextField text];
NSArray *listItemsArray = [list componentsSeparatedByString:#" "];
float firstNumber = [[listItemsArray objectAtIndex: 0] floatValue];
NSString *symbol = [listItemsArray objectAtIndex: 1];
float secondNumber = [[listItemsArray objectAtIndex: 2] floatValue];
{
Calculator* calc = [[Calculator alloc] init];
[calc setNum1:firstNumber];
[calc setNum2:secondNumber];
if ([symbol isEqualToString:#"-"])
{
[calc minus];
}
else if ([symbol isEqualToString:#"+"])
{
[calc add];
}
if ([symbol isEqualToString:#"*"])
{
[calc multiply];
}
else if ([symbol isEqualToString:#"/"])
{
[calc divide];
}
[Answer_TextField setText:[NSString stringWithFormat:#"%d", [calc answer]]];
}
}

Answer 1

I think a better way to do it would be to implement the UITextViewDelegate protocol methods like textViewDidChange:. For example, you could do something like this:
- (void)textViewDidChange:(UITextView *)textView {
NSString *currentText = [textview text];
NSArray *currentItems = [currentText componenetsSeparatedByString:#" "];
float result = 0.0;
//If a valid expression is in the text view
if([currentItems count] > 2) {
float num1 = [[currentItems objectAtIndex:0] floatValue];
float num2 = [[currentItems objectAtIndex:2] floatValue];
NSString *operator = [currentItems objectAtIndex:1];
if([operator isEqualToString:#"+"]) {
result = num1 + num2;
answerTextField.text = [NSString stringWithFormat:#"%f", result];
}
else if([operator isEqualToString:#"-"]) {
result = num1 - num2;
answerTextField.text = [NSString stringWithFormat:#"%f", result];
}
else if([operator isEqualToString:#"*"]) {
result = num1 * num2;
answerTextField.text = [NSString stringWithFormat:#"%f", result];
}
else if([operator isEqualToString:#"/"]) {
result = num1 / num2;
answerTextField.text = [NSString stringWithFormat:#"%f", result];
}
else{
answerTextField.text = #"Invalid Operation";
}
}
}
This would be called every time the user edited the text in the text view. It should work, but I didn't test it out. Make sure that in the header of whatever file this code is in, you do this:
#interface yourClassName : yourSuperclass <UITextViewDelegate> {
//Your instance variables
}
//Your method and property declarations
EDIT:
Let's say I put the - (void)textViewDidChange:(UITextView *)textView code in a file called MyClass.m. The file MyClass.m would then look like this:
#implementation MyClass
- (void)textViewDidChange:(UITextView *)textView {
//All the above code goes here
}
- (void)viewDidLoad
{
[super viewDidLoad];
//INCLUDE THESE LINES
Sum_TextField.delegate = self;
Answer_TextField.delegate = self;
}
- (void)viewDidUnload
{
[super viewDidUnload];
}
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
return YES;
}
#end
In the header file (MyClass.h), I would put this:
#interface MyClass : UIViewController <UITextViewDelegate>
//Note: you don't declare - (void)textViewDidChange:(UITextView *)textView in the header file because you are implementing
//a protocol method.
//MAKE SURE SUM_TEXTFIELD AND ANSWER_TEXTFIELD ARE UITEXTVIEWS NOT UITEXTFIELDS
#property (strong, nonatomic) IBOutlet UITextView *Sum_TextField;
#property (strong, nonatomic) IBOutlet UITextView *Answer_TextField;
#end
Hope this helps!