NSMutableString help Objective C

I currently have the following code:

-(void) inputNumber:(int)number {

    NSString *str;

    str = [NSString stringWithFormat:@"%d", number];
    [strVal appendStri开发者_StackOverflow中文版ng:str];
    txtShowNum.text = strVal;
}

I have already defined NSMutableString *strVal; before in my code.

When the function above executes the field remains blank, but if i were to use:

txtShowNum.text = str;

I get the value that I'm meant to but I obviously need the value concatenated.

Can anyone shed some light on this.

Thanks

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You should allocate an NSMutableString as well in your code, somewhere before this method is called.

E.g. like this:

-(void) inputNumber:(int)number {
    if ( strVal == nil ) strVal = [[NSMutableString alloc] init];
    NSString *str = [NSString stringWithFormat:@"%d", number];
    [strVal appendString:str];
    txtShowNum.text = strVal;
}

There are however some memory issues here. You'd better make strVal a retained property and then do:

    if ( self.strVal == nil ) self.strVal = [NSMutableString string];

---

Your strVal is most probably nil, so you call appendString: on nil which essentially does nothing at all, and setting the text field to nil will erase its contents.

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If you just declared it as a member variable, make sure you initialize it somewhere:

NSMutableString* strVal = @"";

If not, you are just calling a method on a nil object.