Objective-C中的编程Stephen Kochan。第21章，第21.2条

Question

您好！ 的

我在练习21.2时遇到麻烦。在那个练习中，我构建了Fraction计算器。我有9个按钮和数学动作。当我在iOS模拟器上按任意数字（1,2,3或其他任何数字）时，它会生成错误：

    2012-08-05 15:09:05.026 Fraction_Calculator[834:f803] -[ViewController digit5]: unrecognized selector sent to instance 0x6843e00
2012-08-05 15:09:05.029 Fraction_Calculator[834:f803] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[ViewController digit5]: unrecognized selector sent to instance 0x6843e00'
*** First throw call stack:
(0x14b5022 0xeb5cd6 0x14b6cbd 0x141bed0 0x141bcb2 0x14b6e99 0x1b14e 0x1b0e6 0xc1ade 0xc1fa7 0xc1266 0x403c0 0x405e6 0x26dc4 0x1a634 0x139fef5 0x1489195 0x13edff2 0x13ec8da 0x13ebd84 0x13ebc9b 0x139e7d8 0x139e88a 0x18626 0x28ad 0x2815)
terminate called throwing an exception

这意味着什么：＆＃34; 无法识别的选择器发送到实例0x6843e00 ＆＃34;和＆＃34; ＆＃39; - [ViewController digit5]：无法识别的选择器发送到实例0x6843e00＆＃39; ＆＃34;。

以下是该程序的代码：

ViewController.h

代码：Objective-C

#import <UIKit/UIKit.h>
#import "Calculator.h"

@interface ViewController : UIViewController

@property (strong, nonatomic) IBOutlet UILabel *display;

-(void) processDigit: (int) digit;
-(void) processOp: (char) theOp;
-(void) storeFracPart;

-(IBAction) clickDigit: (UIButton *) sender;

-(IBAction) clickPlus;
-(IBAction) clickMinus;
-(IBAction) clickMultiply;
-(IBAction) clickDivide;

-(IBAction) clickOver;
-(IBAction) clickEquals;
-(IBAction) clickClear;

@end

ViewController.m

代码：Objective-C

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController
{
    char                op;
    int                 currentNumber;
    BOOL                firstOperand, isNumerator;
    Calculator          *myCalculator;
    NSMutableString     *displayString;
}

@synthesize display;

-(void) processDigit:(int)digit
{
    currentNumber=currentNumber*10+digit;

    [displayString appendString:[NSString stringWithFormat:@"%i", digit]];
    display.text=displayString;
}

-(IBAction) clickDigit:(UIButton *)sender
{
    int digit=sender.tag;

    [self processDigit: digit];
}

-(void) processOp: (char) theOp
{
    NSString *opStr;

    op=theOp;

    switch(theOp)
    {
            case '+':
                opStr=@"+";
                break;
            case '-':
                opStr=@"-";
                break;
            case '*':
                opStr=@"*";
                break;
            case '/':
                opStr=@"/";
                break;
    }

    [self storeFracPart];
    firstOperand=NO;
    isNumerator=YES;

    [displayString appendString: opStr];
    display.text=displayString;
}

-(void) storeFracPart
{
    if(firstOperand)
    {
       if(isNumerator)
       {
           myCalculator.operand1.numerator=currentNumber;
           myCalculator.operand1.denominator=1;
       }
        else
            myCalculator.operand1.denominator=currentNumber;
    }
    else if (isNumerator)
    {
        myCalculator.operand2.numerator=currentNumber;
        myCalculator.operand2.denominator=1;
    }
    else
    {
        myCalculator.operand2.denominator=currentNumber;
        firstOperand=YES;
    }
currentNumber=0;
}

-(IBAction) clickOver
{
    [self storeFracPart];
    isNumerator=NO;
    [displayString appendString: @"/"];
    display.text=displayString;
}

-(IBAction) clickPlus
{
    [self processOp: '+'];
}

-(IBAction) clickMinus
{
    [self processOp: '-'];
}

-(IBAction) clickMultiply
{
    [self processOp: '*'];
}

-(IBAction) clickDivide
{
    [self processOp: '/'];
}

-(IBAction) clickEquals
{
    if (firstOperand==NO)
    {
        [self storeFracPart];
        [myCalculator performOperation: op];

        [displayString appendString: @"="];
        [displayString appendString: [myCalculator.accumulator convertToString]];
        display.text=displayString;

        currentNumber=0;
        isNumerator=YES;
        firstOperand=YES;
        [displayString setString: @""];        
    }
}

-(IBAction) clickClear
{
    isNumerator=YES;
    firstOperand=YES;
    currentNumber=0;
    [myCalculator clear];

    [displayString setString:@""];
    display.text=displayString;
}

- (void)viewDidLoad
{
    //[super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    firstOperand=YES;
    isNumerator=YES;
    displayString=[NSMutableString stringWithCapacity:40];
    myCalculator=[[Calculator alloc]init];
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

@end

非常感谢！

Answer 1

如果您没有为每个按钮设置标记值，则可能会发生这种情况。例如，对于按钮4，标签应为4，依此类推：

Answer 2

检查数字按钮标签属性（Interface Builder中的UIButton设置）。看起来所有这些都具有 0 的值。只需为按钮设置标签（例如，对于带有数字3的按钮，标签= 3）。