我的单例访问方法通常是一些变种:
static MyClass *gInstance = NULL;
+ (MyClass *)instance
{
@synchronized(self)
{
if (gInstance == NULL)
gInstance = [[self alloc] init];
}
return(gInstance);
}
我能做些什么来改善这一点呢?
我的单例访问方法通常是一些变种:
static MyClass *gInstance = NULL;
+ (MyClass *)instance
{
@synchronized(self)
{
if (gInstance == NULL)
gInstance = [[self alloc] init];
}
return(gInstance);
}
我能做些什么来改善这一点呢?
当前回答
关于单例宏代码的详细解释在Cocoa With Love博客上
http://cocoawithlove.com/2008/11/singletons-appdelegates-and-top-level.html。
其他回答
这也适用于非垃圾收集环境。
@interface MySingleton : NSObject {
}
+(MySingleton *)sharedManager;
@end
@implementation MySingleton
static MySingleton *sharedMySingleton = nil;
+(MySingleton*)sharedManager {
@synchronized(self) {
if (sharedMySingleton == nil) {
[[self alloc] init]; // assignment not done here
}
}
return sharedMySingleton;
}
+(id)allocWithZone:(NSZone *)zone {
@synchronized(self) {
if (sharedMySingleton == nil) {
sharedMySingleton = [super allocWithZone:zone];
return sharedMySingleton; // assignment and return on first allocation
}
}
return nil; //on subsequent allocation attempts return nil
}
-(void)dealloc {
[super dealloc];
}
-(id)copyWithZone:(NSZone *)zone {
return self;
}
-(id)retain {
return self;
}
-(unsigned)retainCount {
return UINT_MAX; //denotes an object that cannot be release
}
-(void)release {
//do nothing
}
-(id)autorelease {
return self;
}
-(id)init {
self = [super init];
sharedMySingleton = self;
//initialize here
return self;
}
@end
这是我放在一起的一个宏:
http://github.com/cjhanson/Objective-C-Optimized-Singleton
它基于马特·加拉格尔的作品 但是将实现改为使用谷歌的Dave MacLachlan所描述的方法swizzling。
我欢迎评论/贡献。
我只是想把这个放在这里,这样我就不会弄丢了。这个的优点是它可以在InterfaceBuilder中使用,这是一个巨大的优势。这是我问的另一个问题:
static Server *instance;
+ (Server *)instance { return instance; }
+ (id)hiddenAlloc
{
return [super alloc];
}
+ (id)alloc
{
return [[self instance] retain];
}
+ (void)initialize
{
static BOOL initialized = NO;
if(!initialized)
{
initialized = YES;
instance = [[Server hiddenAlloc] init];
}
}
- (id) init
{
if (instance)
return self;
self = [super init];
if (self != nil) {
// whatever
}
return self;
}
这不应该是线程安全的,避免第一次调用后昂贵的锁定吗?
+ (MySingleton*)sharedInstance
{
if (sharedInstance == nil) {
@synchronized(self) {
if (sharedInstance == nil) {
sharedInstance = [[MySingleton alloc] init];
}
}
}
return (MySingleton *)sharedInstance;
}
static mySingleton *obj=nil;
@implementation mySingleton
-(id) init {
if(obj != nil){
[self release];
return obj;
} else if(self = [super init]) {
obj = self;
}
return obj;
}
+(mySingleton*) getSharedInstance {
@synchronized(self){
if(obj == nil) {
obj = [[mySingleton alloc] init];
}
}
return obj;
}
- (id)retain {
return self;
}
- (id)copy {
return self;
}
- (unsigned)retainCount {
return UINT_MAX; // denotes an object that cannot be released
}
- (void)release {
if(obj != self){
[super release];
}
//do nothing
}
- (id)autorelease {
return self;
}
-(void) dealloc {
[super dealloc];
}
@end