是否可以将Objective-C块作为@selector参数传递给UIButton？即，有没有办法使以下内容正常工作？
[closeOverlayButton addTarget:self
action:^ {[anotherIvarLocalToThisMethod removeFromSuperview];}
forControlEvents:UIControlEventTouchUpInside];
谢谢
可以，但你需要使用分类。
就像这样：
@interface UIControl (DDBlockActions)
- (void) addEventHandler:(void(^)(void))handler
forControlEvents:(UIControlEvents)controlEvents;
@end
#import <objc/runtime.h>
@interface DDBlockActionWrapper : NSObject
@property (nonatomic, copy) void (^blockAction)(void);
- (void) invokeBlock:(id)sender;
@end
@implementation DDBlockActionWrapper
@synthesize blockAction;
- (void) dealloc {
[self setBlockAction:nil];
[super dealloc];
}
- (void) invokeBlock:(id)sender {
[self blockAction]();
}
@end
@implementation UIControl (DDBlockActions)
static const char * UIControlDDBlockActions = "unique";
- (void) addEventHandler:(void(^)(void))handler
forControlEvents:(UIControlEvents)controlEvents {
NSMutableArray * blockActions =
objc_getAssociatedObject(self, &UIControlDDBlockActions);
if (blockActions == nil) {
blockActions = [NSMutableArray array];
objc_setAssociatedObject(self, &UIControlDDBlockActions,
blockActions, OBJC_ASSOCIATION_RETAIN);
}
DDBlockActionWrapper * target = [[DDBlockActionWrapper alloc] init];
[target setBlockAction:handler];
[blockActions addObject:target];
[self addTarget:target action:@selector(invokeBlock:) forControlEvents:controlEvents];
[target release];
}
@end
解释一下：
DDBlockActionWrapper的自定义“内部限定”类。这是一个简单的类，具有块属性（我们要调用的块），以及一个简单地调用该块的方法。UIControl类别只是实例化其中之一的包装器，将其赋予要被调用的块，然后告诉自己使用该包装器及其invokeBlock:方法作为目标和动作（与通常情况下相同）。UIControl类别使用关联对象来存储DDBlockActionWrappers数组，因为UIControl不保留其目标。该数组旨在确保在应该调用它们时块存在。DDBlockActionWrappers，所以我们进行了一个肮脏的hack，通过一个新的方法替换掉-[UIControl dealloc]，删除关联对象，然后调用原始的dealloc代码。挺棘手的。最后，这段代码是在浏览器中输入的，尚未编译。可能会有一些问题。结果因人而异。
块是对象。将您的块作为target参数传递，将@selector(invoke)作为action参数传递，如下所示：
id block = [^{NSLog(@"Hello, world");} copy];// Don't forget to -release.
[button addTarget:block
action:@selector(invoke)
forControlEvents:UIControlEventTouchUpInside];
invoke 方法并非公共的，也不是以这种方式使用的意图。 - bbumnil而不是@selector(invoke)时起作用。 - k06a不，选择器和代码块在Objective-C中不是兼容的类型（实际上，它们是非常不同的东西）。您需要编写自己的方法并传递其选择器。
@interface NSObject (CategoryNSObject)
- (void) associateValue:(id)value withKey:(NSString *)aKey;
- (id) associatedValueForKey:(NSString *)aKey;
@end
.m
#import "Categories.h"
#import <objc/runtime.h>
@implementation NSObject (CategoryNSObject)
#pragma mark Associated Methods:
- (void) associateValue:(id)value withKey:(NSString *)aKey {
objc_setAssociatedObject( self, (__bridge void *)aKey, value, OBJC_ASSOCIATION_RETAIN );
}
- (id) associatedValueForKey:(NSString *)aKey {
return objc_getAssociatedObject( self, (__bridge void *)aKey );
}
@end
@interface NSInvocation (CategoryNSInvocation)
+ (NSInvocation *) invocationWithTarget:(id)aTarget block:(void (^)(id target))block;
+ (NSInvocation *) invocationWithSelector:(SEL)aSelector forTarget:(id)aTarget;
+ (NSInvocation *) invocationWithSelector:(SEL)aSelector andObject:(__autoreleasing id)anObject forTarget:(id)aTarget;
@end
.m
#import "Categories.h"
typedef void (^BlockInvocationBlock)(id target);
#pragma mark - Private Interface:
@interface BlockInvocation : NSObject
@property (readwrite, nonatomic, copy) BlockInvocationBlock block;
@end
#pragma mark - Invocation Container:
@implementation BlockInvocation
@synthesize block;
- (id) initWithBlock:(BlockInvocationBlock)aBlock {
if ( (self = [super init]) ) {
self.block = aBlock;
} return self;
}
+ (BlockInvocation *) invocationWithBlock:(BlockInvocationBlock)aBlock {
return [[self alloc] initWithBlock:aBlock];
}
- (void) performWithTarget:(id)aTarget {
self.block(aTarget);
}
@end
#pragma mark Implementation:
@implementation NSInvocation (CategoryNSInvocation)
#pragma mark - Class Methods:
+ (NSInvocation *) invocationWithTarget:(id)aTarget block:(void (^)(id target))block {
BlockInvocation *blockInvocation = [BlockInvocation invocationWithBlock:block];
NSInvocation *invocation = [NSInvocation invocationWithSelector:@selector(performWithTarget:) andObject:aTarget forTarget:blockInvocation];
[invocation associateValue:blockInvocation withKey:@"BlockInvocation"];
return invocation;
}
+ (NSInvocation *) invocationWithSelector:(SEL)aSelector forTarget:(id)aTarget {
NSMethodSignature *aSignature = [aTarget methodSignatureForSelector:aSelector];
NSInvocation *aInvocation = [NSInvocation invocationWithMethodSignature:aSignature];
[aInvocation setTarget:aTarget];
[aInvocation setSelector:aSelector];
return aInvocation;
}
+ (NSInvocation *) invocationWithSelector:(SEL)aSelector andObject:(__autoreleasing id)anObject forTarget:(id)aTarget {
NSInvocation *aInvocation = [NSInvocation invocationWithSelector:aSelector
forTarget:aTarget];
[aInvocation setArgument:&anObject atIndex:2];
return aInvocation;
}
@end
NSInvocation *invocation = [NSInvocation invocationWithTarget:self block:^(id target) {
NSLog(@"TEST");
}];
[invocation invoke];
您可以使用调用和标准的Objective-C方法来完成很多事情。例如，您可以使用NSInvocationOperation（initWithInvocation：），NSTimer（scheduledTimerWithTimeInterval：invocation：repeats：）
重点是将您的块转换为NSInvocation更加灵活，可以这样使用：
NSInvocation *invocation = [NSInvocation invocationWithTarget:self block:^(id target) {
NSLog(@"My Block code here");
}];
[button addTarget:invocation
action:@selector(invoke)
forControlEvents:UIControlEventTouchUpInside];
再次声明，这只是一个建议。
有人会告诉我这个方法为什么不对，或者幸运的话，也许不会，所以我要么学到了东西，要么就是有所帮助。
我只是随便写了一下。它非常基础，只是一个薄包装器和一点强制转换。警告一句，它假设你调用的块具有与你使用的选择器匹配的正确签名（即参数数量和类型）。
//
// BlockInvocation.h
// BlockInvocation
//
// Created by Chris Corbyn on 3/01/11.
// Copyright 2011 __MyCompanyName__. All rights reserved.
//
#import <Cocoa/Cocoa.h>
@interface BlockInvocation : NSObject {
void *block;
}
-(id)initWithBlock:(void *)aBlock;
+(BlockInvocation *)invocationWithBlock:(void *)aBlock;
-(void)perform;
-(void)performWithObject:(id)anObject;
-(void)performWithObject:(id)anObject object:(id)anotherObject;
@end
而且
//
// BlockInvocation.m
// BlockInvocation
//
// Created by Chris Corbyn on 3/01/11.
// Copyright 2011 __MyCompanyName__. All rights reserved.
//
#import "BlockInvocation.h"
@implementation BlockInvocation
-(id)initWithBlock:(void *)aBlock {
if (self = [self init]) {
block = (void *)[(void (^)(void))aBlock copy];
}
return self;
}
+(BlockInvocation *)invocationWithBlock:(void *)aBlock {
return [[[self alloc] initWithBlock:aBlock] autorelease];
}
-(void)perform {
((void (^)(void))block)();
}
-(void)performWithObject:(id)anObject {
((void (^)(id arg1))block)(anObject);
}
-(void)performWithObject:(id)anObject object:(id)anotherObject {
((void (^)(id arg1, id arg2))block)(anObject, anotherObject);
}
-(void)dealloc {
[(void (^)(void))block release];
[super dealloc];
}
@end
其实并没有什么神奇的事情发生。只是在调用方法之前，将许多向下转型为void *和类型转换为可用块签名。显然（就像使用performSelector：和相关方法一样），输入的可能组合是有限的，但如果您修改代码，则可以扩展它们。
像这样使用：
BlockInvocation *invocation = [BlockInvocation invocationWithBlock:^(NSString *str) {
NSLog(@"Block was invoked with str = %@", str);
}];
[invocation performWithObject:@"Test"];
它的输出结果为：
2011-01-03 16:11:16.020 BlockInvocation[37096:a0f] 块被调用，str = Test
在目标动作场景中使用，您只需要像这样做：
BlockInvocation *invocation = [[BlockInvocation alloc] initWithBlock:^(id sender) {
NSLog(@"Button with title %@ was clicked", [(NSButton *)sender title]);
}];
[myButton setTarget:invocation];
[myButton setAction:@selector(performWithObject:)];
由于目标在目标-动作系统中不会被保留，因此您需要确保调用对象的生命周期与控件本身一样长。
我很想听听比我更专业的人的意见。
我需要将一个UIButton与UITableViewCell中的一个操作关联起来。我希望避免使用标签来跟踪每个不同单元格中的每个按钮。我认为实现这一点最直接的方法是将一个块“action”与按钮关联起来，如下所示：
[cell.trashButton addTarget:self withActionBlock:^{
NSLog(@"Will remove item #%d from cart!", indexPath.row);
...
}
forControlEvent:UIControlEventTouchUpInside];
感谢@bbum提到imp_implementationWithBlock和class_addMethod，我的实现更加简化了（尽管没有进行广泛测试）：
#import <objc/runtime.h>
@implementation UIButton (ActionBlock)
static int _methodIndex = 0;
- (void)addTarget:(id)target withActionBlock:(ActionBlock)block forControlEvent:(UIControlEvents)controlEvents{
if (!target) return;
NSString *methodName = [NSString stringWithFormat:@"_blockMethod%d", _methodIndex];
SEL newMethodName = sel_registerName([methodName UTF8String]);
IMP implementedMethod = imp_implementationWithBlock(block);
BOOL success = class_addMethod([target class], newMethodName, implementedMethod, "v@:");
NSLog(@"Method with block was %@", success ? @"added." : @"not added." );
if (!success) return;
[self addTarget:target action:newMethodName forControlEvents:controlEvents];
// On to the next method name...
++_methodIndex;
}
@end
使用NSBlockOperation（iOS SDK +5）是否可行？此代码使用ARC，并且是我正在测试的应用程序的简化版本（似乎可以工作，至少表面上如此，但不确定是否存在内存泄漏问题）。
NSBlockOperation *blockOp;
UIView *testView;
-(void) createTestView{
UIView *testView = [[UIView alloc] initWithFrame:CGRectMake(0, 60, 1024, 688)];
testView.backgroundColor = [UIColor blueColor];
[self.view addSubview:testView];
UIButton *btnBack = [UIButton buttonWithType:UIButtonTypeRoundedRect];
[btnBack setFrame:CGRectMake(200, 200, 200, 70)];
[btnBack.titleLabel setText:@"Back"];
[testView addSubview:btnBack];
blockOp = [NSBlockOperation blockOperationWithBlock:^{
[testView removeFromSuperview];
}];
[btnBack addTarget:blockOp action:@selector(start) forControlEvents:UIControlEventTouchUpInside];
}
当然，我不确定这对实际使用有多好。您需要保持对NSBlockOperation的引用，否则我认为ARC会将其销毁。
objc_implementationWithBlock()和class_addMethod()来解决这个问题，比使用关联对象（它们意味着哈希查找不如方法查找高效）略微更有效率。虽然性能差异可能不大，但这是一种替代方案。 - bbumobjc_implementationWithBlock()。 :) - bbumUITableViewCell中使用此代码来处理按钮会导致所需目标操作的重复，因为每个新目标都是一个新实例，并且以前的目标不会为相同的事件清除。您必须首先清除这些目标：for (id t in self.allTargets) { [self removeTarget:t action:@selector(invokeBlock:) forControlEvents:controlEvents]; } [self addTarget:target action:@selector(invokeBlock:) forControlEvents:controlEvents];- Eugene