iOS Tweaks

iOS Developer

[tweakingios-blog]

How to get the size of Keyboard when any UITextView or UITextField is enabled? (Come iOS8 and third-party keyboards, this is going to be very important)

Till iOS7, we had just one type of keyboard in iPhone/iPad. But finally with iOS8, we will be having third party keyboards which can be used throughout the device. Can't wait to install this on my iPhone.

However, many developers have been using a static size to get the size of keyboard heights, which is not a good idea! Come iOS8, this just worsens the situation. Solution?

Its right there in your code. Just that you haven't been using it yet. 

You must be having a similar method for subscribing to keyboard notifications.

- (void)registerForKeyboardNotifications {

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWasShown:) name:UIKeyboardDidShowNotification object:nil];

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillBeHidden:) name:UIKeyboardWillHideNotification object:nil];

}

So in your listeners for these notifications, get this value :

- (void)keyboardWasShown:(NSNotification*)aNotification {

NSDictionary* info = [aNotification userInfo]; CGSize keyboardSize = [[info objectForKey:UIKeyboardFrameBeginUserInfoKey] CGRectValue].size; //this gives the exact size of the keyboard currently used

}

Hope this helps!

Keep coding! 

[tweakingios-blog]

So what's the difference between a message, a selector and a method in Objective C?

Selector - a Selector is the name of a method. You're very familiar with these selectors: alloc, init,release, dictionaryWithObjectsAndKeys:, setObject:forKey:, etc. Note that the colon is part of the selector; it's how we identify that this method requires parameters. Also (though it's extremely rare), you can have selectors like this: doFoo:::. This is a method that takes three parameters, and you'd invoke it like [someObject doFoo:arg1 :arg2 :arg3]. There's no requirement that there be letters before each part of the selector components. As I said, this is extremely rare, and you will not find it used in the Cocoa frameworks. You can work with selectors directly in Cocoa. They have the type SEL: SEL aSelector = @selector(doSomething:) or SEL aSelector = NSSelectorFromString(@"doSomething:");

Message - a message is a selector and the arguments you are sending with it. If I say [dictionary setObject:obj forKey:key], then the "message" is the selector setObject:forKey: plus the arguments obj and key. Messages can be encapsulated in an NSInvocation object for later invocation. Messages are sent to a receiver. (ie, the object that "receives" the message).

Method - a method is a combination of a selector and an implementation (and accompanying metadata). The "implementation" is the actual block of code; it's a function pointer (an IMP). An actual method can be retrieved internally using a Method struct (retrievable from the runtime).

Some other related things:

Method Signature - a method signature represents the data types returned by and accepted by a method. They can be represented at runtime via an NSMethodSignature and (in some cases) a raw char*.

Implementation - the actual executable code of a method. Its type at runtime is an IMP, and it's really just a function pointer. iOS 4.3 includes a new ability to turn a block into an IMP. This is really cool.

One of the fun things to realize is that the name of a method (the selector) is distinct from the implementationof the method (the IMP). This means that you can swap them around, if you're feeling daring. You can also add and remove methods at runtime, because all you're doing is editing an entry in a hash table: the key is the selector, and the value is the IMP of the method. This allows you to do some really crazy and trippy stuff.

Via - Dave DeLong's answer to this question on StackOverflow!

[tweakingios-blog]

Top 5 iOS Developer Podcasts

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[tweakingios-blog]

Ever faced the error "ImageIO: JPEG Application transferred too few scanlines" ? Don't worry. You have a solution!

This error comes up due to two reasons.

1. Maybe you are downloading a .JPEG image and saving it as a .PNG image

Otherwise,

(Most probable one) 2. You are accessing your stored image with the function imageWithContentsOfFile like this : 

UIImage *myImage = [UIImage imageWithContentsOfFile:path];

Instead, fetch data from that file and then create image from that nsdata :

NSData *img = [NSData dataWithContentsOfFile:path]; UIImage *photo = [UIImage imageWithData:img];

Looks like the function imageWithContentsOfFile keeps the file open till the UIImage stays allocated. Hence this much memory stays allocated without any use of it.

  Happpy Coding! :)

[tweakingios-blog]

A classic description of SQL Joins!

[tweakingios-blog]

Looping through NSDates between two dates

#define SECONDS_IN_A_DAY 86400 NSDate* todayDate = [NSDate date]; NSDate* earlierDate = [NSDate dateWithTimeInterval: 5 * SECONDS_IN_A_DAY * (-1) sinceDate:[NSDate date]]; for(NSDate* currentDate = [NSDate dateWithTimeInterval:0 sinceDate:earlierDate]; [currentDate compare:todayDate] < 0; currentDate = currentDate dateByAddingTimeInterval:SECONDS_IN_A_DAY) { NSLog(@"%@ is in between %@ and %@",currentDate, todayDate, earlierDate); }

This would loop through NSDates between date for today and date for 5 days before.

If you want to loop through today and a future date or through two different dates then just change the values for todayDate and earlierDate accordingly.

Enjoy Coding! :)

[tweakingios-blog]

Sorting a NSMutableArray containing NSDictionary by a key inside the NSDictionary

So, when you have an NSMutableArray of UserElements which are contained in NSDictionaries and now if you want to sort it with reference to a key inside these Dictionaries, for example LAST NAME, then, you can acheive it with the help of NSSortDescriptors...

Do the following : 

NSSortDescriptor *lastNameDescriptor = [[NSSortDescriptor alloc] initWithKey:@"lastName" ascending:YES]; self.userArray = [NSMutableArray arrayWithArray:[self.userArray sortedArrayUsingDescriptors:[NSArray arrayWithObjects:lastNameDescriptor,nil]]]; [yourSortDescriptor release]; NSLog(@"sorted array -->> %@",[self.userArray description]);

Happy Coding!

[tweakingios-blog]

Prevent disabling of NSTimer Actions while scrolling inside a UIScrollView

Supposing you have a UIViewController, where you are currently having NSTimer actions going on repeatedly.

Now, if a User starts to scroll inside a UIScrollView then the NSTimer actions would be paused.

This is the default behaviour of iOS sdk. To prevent this from happening, use the following code : 

[[NSRunLoop mainRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];

This adds the Timer to the main NSRunLoop so as to never stop/pause from executing.

Happy Coding all of you!! :)

[tweakingios-blog]

Creating a child mutable dictionary from parent mutable dictionary, with both being independent of each other

When we create a child mutable dictionary, which is an exact replica of another parent mutable dictionary, often there would be a situation, where you change value for one key of the child dictionary and the value for same key would be changed for the parent dictionary too.

And, vice-versa. Changing values for parent dictionary would reflect for the images of child dictionary.

For this, what we would have to do is, Deep Copy. And deep copy, in true sense, for NSMutableDictionary or NSMutableArray would be done very easily with NSCoding (serialization) protocol.

  - (id) deepCopy:(id)mutableObjectToBeCopied

{

    NSData *buffer = [NSKeyedArchiver archivedDataWithRootObject: mutableObjectToBeCopied];

    return [NSKeyedUnarchiver unarchiveObjectWithData: buffer];

}

[tweakingios-blog]

Getting the name of Controllers for your navigation Stack

Logging all the UIViewControllers of your current Navigation Stack cycle. 

This would help in scenarios like, you have to popUp from the present UIViewController to any particular parent ViewController but you might not know what type it is currently.

    for (UIViewController *aViewController in [self.navigationController viewControllers]) {

        NSLog(@"view controller is of type %@",(NSStringFromClass([aViewController class])));

}

It gives you a log as such.

view controller is of type RootViewController

view controller is of type CustomTabBarController

view controller is of type ChildViewController

And so on..... Until the Current View Controller.

Happy Coding!