如何使用带参数的事件处理程序？

Posted 2023-03-12

【中文标题】如何使用带参数的事件处理程序？

【英文标题】：How do you use event handlers with parameters?

【发布时间】：2010-10-08 05:53:58

【问题描述】：

我正试图弄清楚这些事件是如何运作的。在 iTunes U 上斯坦福课程的视频 4 中，Alan Cannistraro 说有

“三种不同风格的动作方法选择器类型 - (void)actionMethod; - (void)actionMethod:(id)sender; - (void)actionMethod:(id)sender withEvent:(UIEvent *)event;"

我想我会用一个简单的加法程序来试试它们 - 你输入 2 个数字，当你输入总和时，就会在第三个 UITextField 中获得位置。我有一个无参数签名的方法，它工作正常。当我使用 sender 参数将其更改为第二个时，代码将停止调用该方法。

这行得通：

-(void) setSum 
float a1 = addend1.text.floatValue;
float a2 = addend2.text.floatValue;
float thesum = a1 + a2;
NSString * ssum = [NSString stringWithFormat:@"%g", thesum]; 
sum.text = ssum;


-(void)awakeFromNib 
SEL setSumMethod = @selector(setSum);
[addend1 addTarget: self action: setSumMethod forControlEvents: UIControlEventEditingChanged];
[addend2 addTarget: self action: setSumMethod forControlEvents: UIControlEventEditingChanged];
// awakeFromNib

这会运行但 setSum 没有被调用：

-(void) setSum:(id) sender 
float a1 = addend1.text.floatValue;
float a2 = addend2.text.floatValue;
float thesum = a1 + a2;
NSString * ssum = [NSString stringWithFormat:@"%g", thesum]; 
sum.text = ssum;



-(void)awakeFromNib 
SEL setSumMethod = @selector(setSum:);
[addend1 addTarget: self action: setSumMethod forControlEvents: UIControlEventEditingChanged];
[addend2 addTarget: self action: setSumMethod forControlEvents: UIControlEventEditingChanged];
// awakeFromNib

那么，问题是其他事件方法类型何时起作用？似乎只有第一个适用。

TIA

标记

【参考方案1】：

很老的问题，我知道...

我刚刚测试过：

- (void) onField

    NSLog(@"onField");


- (void) onField:(id) sender

    NSLog(@"onField: %@", sender);


- (void) onField:(id) sender event:(id)event

    NSLog(@"onField: %@\n%@", sender, event);


- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions

    UITextField *field = [[[UITextField alloc] initWithFrame:CGRectMake(0, 100, 100, 100)] autorelease];
    [field setText:@"text"];
    [field addTarget:self action:@selector(onField) forControlEvents:UIControlEventEditingChanged];
    [field addTarget:self action:@selector(onField:) forControlEvents:UIControlEventEditingChanged];
    [field addTarget:self action:@selector(onField:event:) forControlEvents:UIControlEventEditingChanged];
    [window addSubview:field];

    [window makeKeyAndVisible];

    return YES;

结果：

2010-11-04 11:35:59.940 Untitled[599:207] onField
2010-11-04 11:35:59.941 Untitled[599:207] onField: <UITextField: 0x6a0c1f0; frame = (0 100; 100 100); text = 'textsfr'; clipsToBounds = YES; opaque = NO; layer = <CALayer: 0x6a0c350>>
2010-11-04 11:35:59.944 Untitled[599:207] onField: <UITextField: 0x6a0c1f0; frame = (0 100; 100 100); text = 'textsfr'; clipsToBounds = YES; opaque = NO; layer = <CALayer: 0x6a0c350>>
(null)

所以它只是工作。问题出在其他地方。