NSMutableArray addObject为零吗？

Question

I am new to iOS dev,here is my first app-calculator, But the NSMuteableArray "_numberArrayWaitingForCalculate" always be "nil",I don't know what to do???

Here is the interface

@interface demoViewController ()
@property (strong,nonatomic)NSString *valueString;
@property (strong,nonatomic)NSMutableArray *numberArrayWaitingForCalculate;
@end

here is the implement 1

@implementation demoViewController
@synthesize numberArrayWaitingForCalculate=_numberArrayWaitingForCalculate;

- (NSMutableArray *)numberWaitingForCalculate
{
    if(!_numberArrayWaitingForCalculate)
        _numberArrayWaitingForCalculate=[[NSMutableArray alloc]init];

    return _numberArrayWaitingForCalculate;
}

here is the tapNumber method

- (IBAction)tapNumber:(UIButton *)numberButton {
    if(LastButtonWasMode)
    {
        _valueString=@"";
        LastButtonWasMode=NO;
    }

    NSString *numberAsString = numberButton.currentTitle;
    _valueString=[_valueString stringByAppendingString:numberAsString];
    result.text=[NSString stringWithFormat:@"%@",_valueString];
    }

here is tapPlus method

- (IBAction)tapPlus:(id)sender {
    [_numberArrayWaitingForCalculate addObject:[NSNumber numberWithInt:[_valueString intValue]]];
    resultOfAllNumberInputBefore +=[_valueString intValue];
   [self setMode:1];

}

Answer 1

The following line should be using the property and not the instance variable. ie you're not actually calling the getter that allocates the array.

Change this line:

[_numberArrayWaitingForCalculate addObject:[NSNumber numberWithInt:[_valueString intValue]]];

to:

[self.numberArrayWaitingForCalculate addObject:[NSNumber numberWithInt:[_valueString intValue]]];

Answer 2

You created a getter that "lazy loads" the mutable array (meaning that you create it if it doesn't exist already. That's a valid approach.

However, if you do that, you need to ALWAYS use the getter. You're using the iVar directly (_numberArrayWaitingForCalculate). Don't do that. Replace all instances of "_numberArrayWaitingForCalculate" with [self numberArrayWaitingForCalculate] except in the implementation of your getters/setters and probably your dealloc method.

So your tapPlus method should read:

- (IBAction)tapPlus:(id)sender 
{
    [[self numberArrayWaitingForCalculate] addObject:[NSNumber numberWithInt:[_valueString intValue]]];
    resultOfAllNumberInputBefore +=[_valueString intValue];
   [self setMode:1];
}

EDIT:

By the way, for something as lightweight as an empty mutable array, I think I would take a different approach. Rather than lazy-loading the array in a getter, I would create an init method for my class that created an empty mutable array and installed it in the iVar.

Objects like view controllers can be initialized more than one way. It might get initialized with initWithNibName:bundle: or with initWithCoder:

What I do in that case is to create a method doInitSetup, and call it from both places.