Elton's Blog

- (NSString *)createUUID
{
  // Create universally unique identifier (object)
  CFUUIDRef uuidObject = CFUUIDCreate(kCFAllocatorDefault);
 
  // Get the string representation of CFUUID object.
  NSString *uuidStr = (NSString *)CFUUIDCreateString(kCFAllocatorDefault, uuidObject);
 
  // If needed, here is how to get a representation in bytes, returned as a structure
  // typedef struct {
  //   UInt8 byte0;
  //   UInt8 byte1;
  //   ...
  //   UInt8 byte15;
  // } CFUUIDBytes;
  CFUUIDBytes bytes = CFUUIDGetUUIDBytes(uuidObject);
 
  CFRelease(uuidObject);
 
  return uuidStr;
}

int main(int argc, char**argv) 
{
         NSLog(@"create an autorelasePooln");
         NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];   
 
         NSLog(@"create an instance of ClassA and autoreleasen");
         ClassA *obj1 = [[[ClassA alloc] init] autorelease];
         NSDate *now = [[NSDate alloc] init];
         NSTimer *timer = [[NSTimer alloc] initWithFireDate:now
                   interval:0.0
                   target:obj1
                   selector:@selector(createClassB)
                   userInfo:nil
                   repeats:NO];
         NSRunLoop *runLoop = [NSRunLoop currentRunLoop];
         [runLoop addTimer:timer forMode:NSDefaultRunLoopMode];
         [timer release];
         [now release];
         [runLoop run]; //在新loop中调用一函数，生成ClassB的autorelease实例
 
         NSLog(@"releasing autorelasePooln");
         [pool release];
         NSLog(@"autorelasePool is releasedn");
         return 0;
}

create an autorelasePool
create an instance of ClassA and autorelease
create an instance of ClassB and autorelease
ClassB destroyed
releasing autorelasePool
ClassA destroyed
autorelasePool is released

int main(int argc, char**argv) 
{
         NSLog(@"No autorelasePool createdn");
 
         NSLog(@"create an instance of ClassAn");
         ClassA *obj1 = [[ClassA alloc] init];
         NSDate *now = [[NSDate alloc] init];
         NSTimer *timer = [[NSTimer alloc] initWithFireDate:now
                   interval:0.0
                   target:obj1
                   selector:@selector(createClassB)
                   userInfo:nil
                   repeats:NO];
         NSRunLoop *runLoop = [NSRunLoop currentRunLoop];
         [runLoop addTimer:timer forMode:NSDefaultRunLoopMode];
         [timer release];
         [now release];
         [runLoop run]; //在新loop中调用一函数，生成ClassB的autorelease实例
         NSLog(@"Manually release the instance of ClassAn");
         [obj1 release];
 
         return 0;
}

No autorelasePool created
create an instance of ClassA
create an instance of ClassB and autorelease
ClassB destroyed
Manually release the instance of ClassA
ClassA destroyed

NSString *str1 = @”constant string”;

NSString *str2 = [NSString stringWithFormat:@”123”];

@interface ClassA : NSObject
{
         ClassB *objB;
}
 
-(ClassB *) getObjB;
-(void) setObjB:(ClassB *) value;
@end
 
@implementation ClassA
-(ClassB*) getObjB
{
         return objB;
}
 
-(void) setObjB:(ClassB*) value
{
         if (objB != value)
         {
                   [objB release];
                   objB = [value retain];
         }
}

-(void) dealloc
{
         [objB release];
         [super dealloc];
}

ClassA *obj1 = [[ClassA alloc] init];

ClassA *obj1 = [[[ClassA alloc] init] autorelease];

[obj1 release];
obj1 = nil;

ClassA *obj2 = obj1;
[obj2 retain];
//do something
[obj2 release];
obj2 = nil;

ClassA *Func1()
{
  ClassA *obj = [[[ClassA alloc]init]autorelease];
  return obj;
}

-(void) dealloc
{
         …
         [super dealloc];
}

ClassB *objB;

@property (retain) ClassB* objB;

@synthesize objB;

[objB release];

@interface ClassA : NSObject
{
         ClassB* objB;
}
 
@property (retain) ClassB* objB;
@end
 
@implementation ClassA
@synthesize objB;
-(void) dealloc
{
         [objB release];
         [super dealloc];
}
@end

void funcNoAutorelease()
{
         ClassB *objB1 = [[ClassB alloc]init];
         ClassA *objA = [[ClassA alloc]init];
         objA.objB = objB1;
         [objB1 release];
         [objA release];
}
 
void funcAutorelease()
{
         ClassB *objB1 = [[[ClassB alloc]init] autorelease];
         ClassA *objA = [[[ClassA alloc]init] autorelease];
         objA.objB = objB1;
}

ClassA *obj1 = [[ClassA alloc] init];

[obj1 dealloc];

ClassA *obj1 = [[ClassA alloc] init];
ClassA *obj2 = obj1;
[obj1 hello]; //输出hello
[obj1 dealloc];
[obj2 hello]; //能够执行这一行和下一行吗？
[obj2 dealloc];

ClassA *obj1 = [[ClassA alloc] init]; //对象生成时，retain count = 1
[obj1 release]; //release使retain count减1，retain count = 0，dealloc自动被调用,对象被销毁

ClassA *obj1 = [[ClassA alloc] init]; //retain count = 1
ClassA *obj2 = obj1; //retain count = 1
[obj1 hello]; //输出hello
[obj1 release]; //retain count = 0，对象被销毁
[obj2 hello];
[obj2 release];

ClassA *obj1 = [[ClassA alloc] init]; //retain count = 1
ClassA *obj2 = obj1; //retain count = 1
[obj2 retain]; //retain count = 2
[obj1 hello]; //输出hello
[obj1 release]; //retain count = 2 – 1 = 1
[obj2 hello]; //输出hello
[obj2 release]; //retain count = 0，对象被销毁

ClassA *obj1 = [[[ClassA alloc] init] autorelease]; //retain count = 1 但无需调用release

ClassA *obj1 = [[[ClassA alloc] init] autorelease]; //retain count = 1
ClassA *obj2 = obj1; //retain count = 1
[obj2 retain]; //retain count = 2
[obj1 hello]; //输出hello
//对于obj1，无需调用（实际上不能调用）release
[obj2 hello]; //输出hello
[obj2 release]; //retain count = 2-1 = 1

NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

ClassA *obj1 = [[[ClassA alloc] init] autorelease]; //retain count = 1，把此对象加入autorelease pool中

int main (int argc, const char *argv[])
{
NSAutoreleasePool *pool;
pool = [[NSAutoreleasePool alloc] init];
 
// do something
 
[pool release];
return (0);
} // main

int main (int argc, const char *argv[])
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
int i, j;
for (i = 0; i < 100; i++ )
{
 for (j = 0; j < 100000; j++ )
    [NSString stringWithFormat:@"1234567890"];//产生的对象是autorelease的。
}
[pool release];
return (0);
} // main

int main (int argc, const char *argv[])
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
int i, j;
for (i = 0; i < 100; i++ )
{
 NSAutoreleasePool *loopPool = [[NSAutoreleasePool alloc] init];
 for (j = 0; j < 100000; j++ )
    [NSString stringWithFormat:@"1234567890"];//产生的对象是autorelease的。
 [loopPool release];
}
[pool release];
return (0);
} // main

//  UIImage+Scale.h
 
@interface UIImage (scale)
 
-(UIImage*)scaleToSize:(CGSize)size;
 
@end

//  UIImage+Scale.h
 
#import "UIImage+Scale.h"
 
@implementation UIImage (scale)
 
-(UIImage*)scaleToSize:(CGSize)size
{
  // 创建一个bitmap的context
  // 并把它设置成为当前正在使用的context
  UIGraphicsBeginImageContext(size);
 
  // 绘制改变大小的图片
  [self drawInRect:CGRectMake(0, 0, size.width, size.height)];
 
  // 从当前context中创建一个改变大小后的图片
  UIImage* scaledImage = UIGraphicsGetImageFromCurrentImageContext();
 
  // 使当前的context出堆栈
  UIGraphicsEndImageContext();
 
  // 返回新的改变大小后的图片
  return scaledImage;
}
 
@end

// 创建图片
UIImage *image = [UIImage imageNamed:@"myImage.png"];
 
// 更改图片大小
UIImage *scaledImage = [image scaleToSize:CGSizeMake(25.0f, 35.0f)];

@interface Controller : NSObject
{
	NSString *something;
}
 
+ (void)thisIsAStaticMethod;
- (void)thisIsAnInstanceMethod;
 
@end
 
@interface Controller (Private)
 
- (void)thisIsAPrivateMethod;
 
@end

FileOverviewViewController *fileOverviewViewController = [[FileOverviewViewController alloc] initWithNibName:@"FileOverviewView" bundle:nil];
// AAAAA
[self.navigationController pushViewController:fileOverviewViewController animated:YES];
// BBBBBB

Declaration: typedef struct _NSRange {
   NSUInteger location;
   NSUInteger length;
} NSRange;

Declaration: NSRange NSMakeRange (
   NSUInteger loc,
   NSUInteger len
);

        NSRange range = NSMakeRange(0, 5); 
	NSArray *subArray = [self.states subarrayWithRange:range];

//Using longitude and latitude to drop a pin on Google maps
	float longitude = 38.892219;
	float latitude = -77.034674;
 
	NSString *url = [NSString stringWithFormat: @"http://maps.google.com/?q=%f,%f",
	                     longitude,
	                     latitude];
 
	[[UIApplication sharedApplication] openURL:[NSURL URLWithString:url]];

//URL to map address
NSString *url = @"http://maps.google.com/?q=Constitution+Avenue+Northwest+Washington+DC";
 
[[UIApplication sharedApplication] openURL:[NSURL URLWithString:url]];