iOS知识小集 第一期

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@interface TestStringClass ()
@property (nonatomic, strong) NSString *strongString;
@property (nonatomic, copy) NSString *copyedString;
@end

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- (void)test {
NSString *string = [NSString stringWithFormat:@"abc"];
self.strongString = string;
self.copyedString = string;

NSLog(@"origin string: %p, %p", string, &string);
NSLog(@"strong string: %p, %p", strongString, &strongString);
NSLog(@"copy string: %p, %p", copyedString, ©edString);
}

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origin string: 0x7fe441592e20, 0x7fff57519a48
strong string: 0x7fe441592e20, 0x7fe44159e1f8
copy string: 0x7fe441592e20, 0x7fe44159e200

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NSString *string = [NSString stringWithFormat:@"abc"];

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NSMutableString *string = [NSMutableString stringWithFormat:@"abc"];

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origin string: 0x7ff5f2e33c90, 0x7fff59937a48
strong string: 0x7ff5f2e33c90, 0x7ff5f2e2aec8
copy string: 0x7ff5f2e2aee0, 0x7ff5f2e2aed0

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NSAssert / NSCAssert
NSParameterAssert / NSCParameterAssert

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*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'true is not equal to false'

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// 返回与当前线程的NSAssertionHandler对象。
// 如果当前线程没有相关的断言处理器，则该方法会创建一个并指定给当前线程
+ (NSAssertionHandler *)currentHandler

// 当NSCAssert或NSCParameterAssert断言失败时，会调用这个方法
- (void)handleFailureInFunction:(NSString *)functionName file:(NSString *)object lineNumber:(NSInteger)fileName description:(NSString *)line, format,...

// 当NSAssert或NSParameterAssert断言失败时，会调用这个方法
- (void)handleFailureInMethod:(SEL)selector object:(id)object file:(NSString *)fileName lineNumber:(NSInteger)line description:(NSString *)format, ...

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NSString * const NSAssertionHandlerKey;

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@interface LoggingAssertionHandler : NSAssertionHandler

@end

@implementation LoggingAssertionHandler

- (void)handleFailureInMethod:(SEL)selector
object:(id)object
file:(NSString *)fileName
lineNumber:(NSInteger)line
description:(NSString *)format, ...
{
NSLog(@"NSAssert Failure: Method %@ for object %@ in %@#%i", NSStringFromSelector(selector), object, fileName, line);
}

- (void)handleFailureInFunction:(NSString *)functionName
file:(NSString *)fileName
lineNumber:(NSInteger)line
description:(NSString *)format, ...
{
NSLog(@"NSCAssert Failure: Function (%@) in %@#%i", functionName, fileName, line);
}

@end

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- (BOOL)application:(UIApplication *)application
didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
NSAssertionHandler *assertionHandler = [[LoggingAssertionHandler alloc] init];
[[[NSThread currentThread] threadDictionary] setValue:assertionHandler
forKey:NSAssertionHandlerKey];
// ...
return YES;
}

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#ifndef IBOutletCollection
#define IBOutletCollection(ClassName)
#endif

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#define IBOutletCollection(ClassName) attribute((iboutletcollection(ClassName)))

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@property (strong, nonatomic) IBOutletCollection(UIScrollView) NSArray *scrollViews;

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- (void)setupScrollViewImages
{
for (UIScrollView *scrollView in self.scrollViews) {
[self.imagesData enumerateObjectsUsingBlock:^(NSString *imageName, NSUInteger idx, BOOL *stop) {

UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(CGRectGetWidth(scrollView.frame) * idx, 0, CGRectGetWidth(scrollView.frame), CGRectGetHeight(scrollView.frame))];
imageView.contentMode = UIViewContentModeScaleAspectFill;
imageView.image = [UIImage imageNamed:imageName];
[scrollView addSubview:imageView];
}];
}
}

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@property (strong, nonatomic) IBOutletCollection(UIScrollView) NSSet *scrollViews;

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(lldb) po self.scrollViews
<__NSArrayI 0x1740573d0>(
<UIScrollView: 0x12d60d770; frame = (0 0; 320 162); clipsToBounds = YES; autoresize = W+H; gestureRecognizers = <NSArray: 0x1740574f0>; layer = <CALayer: 0x174229480>; contentOffset: {0, 0}; contentSize: {0, 0}>,
<UIScrollView: 0x12d60dee0; frame = (0 0; 320 161); clipsToBounds = YES; autoresize = W+H; gestureRecognizers = <NSArray: 0x174057790>; layer = <CALayer: 0x1742297c0>; contentOffset: {0, 0}; contentSize: {0, 0}>,
<UIScrollView: 0x12d60e650; frame = (0 0; 320 163); clipsToBounds = YES; autoresize = W+H; gestureRecognizers = <NSArray: 0x1740579a0>; layer = <CALayer: 0x1742298e0>; contentOffset: {0, 0}; contentSize: {0, 0}>
)

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NSLock *lock = [[NSLock alloc] init];

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

static void (^RecursiveMethod)(int);

RecursiveMethod = ^(int value) {

[lock lock];
if (value > 0) {

NSLog(@"value = %d", value);
sleep(2);
RecursiveMethod(value - 1);
}
[lock unlock];
};

RecursiveMethod(5);
});

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value = 5
* -[NSLock lock]: deadlock (<NSLock: 0x1700ceee0> '(null)')    * Break on _NSLockError() to debug.

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NSRecursiveLock *lock = [[NSRecursiveLock alloc] init];

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value = 5
value = 4
value = 3
value = 2
value = 1

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// 在给定的时间之前去尝试请求一个锁
- (BOOL)lockBeforeDate:(NSDate *)limit

// 尝试去请求一个锁，并会立即返回一个布尔值，表示尝试是否成功
- (BOOL)tryLock

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NSRecursiveLock *lock = [[NSRecursiveLock alloc] init];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

static void (^RecursiveMethod)(int);

RecursiveMethod = ^(int value) {

[lock lock];
if (value > 0) {

NSLog(@"value = %d", value);
sleep(2);
RecursiveMethod(value - 1);
}
[lock unlock];
};

RecursiveMethod(5);
});

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

sleep(2);
BOOL flag = [lock lockBeforeDate:[NSDate dateWithTimeIntervalSinceNow:1]];
if (flag) {
NSLog(@"lock before date");

[lock unlock];
} else {
NSLog(@"fail to lock before date");
}
});

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value = 5
value = 4
fail to lock before date
value = 3
value = 2
value = 1

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@property(copy) NSString *name

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enum {
// 默认行为，强引用集合中的对象，等同于NSSet
NSHashTableStrongMemory             = 0,

// 在将对象添加到集合之前，会拷贝对象
NSHashTableCopyIn                   = NSPointerFunctionsCopyIn,

// 使用移位指针(shifted pointer)来做hash检测及确定两个对象是否相等；
// 同时使用description方法来做描述字符串
NSHashTableObjectPointerPersonality = NSPointerFunctionsObjectPointerPersonality,

// 弱引用集合中的对象，且在对象被释放后，会被正确的移除。
NSHashTableWeakMemory               = NSPointerFunctionsWeakMemory
};

typedef NSUInteger NSHashTableOptions;

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// 具体调用如下
@implementation TestHashAndMapTableClass {
NSMutableDictionary *_dic;
NSSet               *_set;
NSHashTable         *_hashTable;
}

- (instancetype)init {
self = [super init];

if (self) {
[self testWeakMemory];
NSLog(@"hash table [init]: %@", _hashTable);
}
return self;
}

- (void)testWeakMemory {
if (!_hashTable) {
_hashTable = [NSHashTable weakObjectsHashTable];
}

NSObject *obj = [[NSObject alloc] init];
[_hashTable addObject:obj];
NSLog(@"hash table [testWeakMemory] : %@", _hashTable);
}

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hash table [testWeakMemory] : NSHashTable {
[6] <NSObject: 0x7fa2b1562670>
}
hash table [init]: NSHashTable {
}

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Unknown class XXViewController in Interface Builder file.

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Unbalanced calls to begin/end appearance transitions for ...

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occurs when you try and display a new viewcontroller before the current view controller is finished displaying.

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Basically you are trying to push two view controllers onto the stack at almost the same time.