There are 3 methods to substring a NSString.
NSLog([@"1234567890" substringFromIndex:4]); NSLog([@"1234567890" substringToIndex:6]); NSLog([@"1234567890" substringWithRange:NSMakeRange(3, 5)]);
Category Archives: Objective-C
Objective-C – Rounding float numbers
In Objective-C, you can use the ceil(), floor() and lroundf() functions to round a float number.
// ceil() NSLog(@"ceil(1.4f) : %f", ceil(1.4f)); NSLog(@"ceil(1.5f) : %f", ceil(1.5f)); // floor() NSLog(@"floor(1.5f) : %f", floor(1.5f)); NSLog(@"floor(1.5f) : %f", floor(1.5f)); // lroundf() NSLog(@"lroundf(1.4f): %d", lroundf(1.4f)); NSLog(@"lroundf(1.5f): %d", lroundf(1.5f));
Objective-C – NSDictionary Example
NSDictionary is a useful object to store key-pair values just like HashMap in Java.
You can create and iterate a NSDictionary as follow
// Create a NSDictionary
NSArray *keys = [NSArray arrayWithObjects:@"key1", @"key2", @"key3", nil];
NSArray *objs = [NSArray arrayWithObjects:@"obj1", @"obj2", @"obj3", nil];
NSDictionary *dict = [NSDictionary dictionaryWithObjects:objs forKeys:keys];
// Iterate it
for (id key in dict) {
NSLog(@"key: %@ value:%@", key, [dict objectForKey:key]);
}
Objective-C – Sleep Function
In Objective-C, you can use the sleepForTimeInterval class method of NSThread to sleep the program.
// Sleep the program for 10 second [NSThread sleepForTimeInterval:10.0];
Done =)
Reference: NSThread Class Reference
Objective-C – How to Shuffle a NSMutableArray
You can use the following piece of code to randomize/shuffle the objects inside a NSMutableArray.
/* anArray is a NSMutableArray with some objects */
srandom(time(NULL));
NSUInteger count = [anArray count];
for (NSUInteger i = 0; i < count; ++i) {
int nElements = count - i;
int n = (random() % nElements) + i;
[anArray exchangeObjectAtIndex:i withObjectAtIndex:n];
}
Update @ 2012-07-18: Suggestion from kimbebot
/* anArray is a NSMutableArray with some objects */
NSUInteger count = [anArray count];
for (NSUInteger i = 0; i < count; ++i) {
int nElements = count - i;
int n = (arc4random() % nElements) + i;
[anArray exchangeObjectAtIndex:i withObjectAtIndex:n];
}
Done =)
Reference: StackOverflow – What’s the Best Way to Shuffle an NSMutableArray?
Objective-C – Display Date and Time Using NSDateFormatter
You can get the Date and Time in NSString using NSDateFormatter.
// Get current datetime NSDate *currentDateTime = [NSDate date]; // Instantiate a NSDateFormatter NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init]; // Set the dateFormatter format [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"]; // Get the date time in NSString NSString *dateInString = [dateFormatter stringFromDate:currentDateTime]; // Release the dateFormatter [dateFormatter release];
Continue reading Objective-C – Display Date and Time Using NSDateFormatter
Objective-C – Convert NSString File Path to NSURL and Vice Versa
Convert NSString to NSURL
NSURL *fileURL = [[NSURL alloc] initFileURLWithPath:filePath]; /* OR */ NSURL *fileURL = [NSURL fileURLWithPath:filePath];
Convert NSURL to NSString
// The output string will have the file:// prefix NSString *filePath= [fileURL absoluteString]; // The output string will have the file path only NSString *filePath= [fileURL path];
Updated @ 2011-01-10: Thanks for the comments of Brandon and Antal.
Objective-C – Create a Static Class
Update @ 2012-08-07: As mentioned by Siby, the approach in this article may cause memory leak. Please try to use singleton as shown in the following link.
The Objective-C Singleton
–
Like Java, i would like to add a Static Class such that i could call static variables and static methods in any where.
In Objective-C, you can create a static variable using a static modifier.
For static method which is also known as class method, you can use the + sign instead of the – sign when declaring the method.
I have created a Utility class as follow.
Utility.h
@interface Utility : NSObject + (int)getNumber; + (void)setNumber:(int)number; @end
Utility.m
#import "Utility.h"
@implementation Utility
static int number = 1;
+ (int)getNumber {
return number;
}
+ (void)setNumber:(int)newNumber {
number = newNumber;
}
+ (id)alloc {
[NSException raise:@"Cannot be instantiated!" format:@"Static class 'ClassName' cannot be instantiated!"];
return nil;
}
@end
Now i would like to get and set this static variable when loading HelloView. so I need to modify the HelloViewController.m.
HelloController.m
#import "Utility.h"
@implementation HelloController
...
- (void)viewDidLoad {
[super viewDidLoad];
NSLog(@"number = %d", [Utility getNumber]);
[Utility setNumber:3];
NSLog(@"number = %d", [Utility getNumber]);
}
...
@end
Run the application and check the Debugger Console.
2010-04-09 17:27:18.864 HelloWorld[10860:20b] number = 1 2010-04-09 17:27:18.874 HelloWorld[10860:20b] number = 3
Done =)
Update @ 2011-08-25: Add (id)alloc in Utility.m to avoid the class being instantiated. Thanks Liam. =)
Objective-C – Format Specifier in NSString
Ususally we use the Format Specifier in NSLog() to show the debug output. For Example:
NSString* name = @"Yuen Ying Kit"; int age = 26; NSLog(@"My name is %@", name); NSLog(@"I am %i years old", age);
Objective-C – Convert NSString to int and Vice Versa
Convert NSString to int
NSString *aNumberString = @"123"; int i = [aNumberString intValue];
Convert int to NSString
int aNumber = 123; NSString *aString = [NSString stringWithFormat:@"%d", aNumber];
Eureka! 