I have an iOS app with about 50 views. I want to perform some operation after every 5th screen that the user visits. I know I can create a sort of global counter variable and update that on viewDidLoad of each view, and if count is 5, then perform that operation, and reset that counter variable. Is there a better, more efficient way of doing this? Also looking ahead, if I require to alter something, I would rather do it in a single file than all of my views. Would really appreciate some inputs on this.
I would create a singleton class to keep track of your counter logic, create a base class for all of your view controllers and then make your call to the counter singleton in the viewDidLoad of your base class.
I think something like this would work for you:
#interface ViewCountManager()
#property(nonatomic) NSInteger viewCount;
#end
#implementation ViewCountManager
#define kOperateOnCount 5
+(ViewCountManager *)viewCountManager
{
static ViewCountManager *viewCountManager = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
viewCountManager = [[self alloc] init];
});
return viewCountManager;
}
-(BOOL)shouldPerformOperation
{
BOOL retValue = NO;
if( self.viewCount == kOperateOnCount - 1 )
{
retValue = YES;
self.viewCount = 0;
}
else
{
self.viewCount++;
}
return retValue;
}
#end
#implementation CountedViewController
-(void)viewDidLoad:(BOOL)animated
{
[super viewDidLoad:animated];
BOOL shouldPerform = [[ViewCountManager viewCountManager] shouldPerformOperation];
[self performOperation];
}
#end
Related
I have two independent delegate methods in a class.
- (void)delegateMethod1:(id)data {
self.data = data;
}
- (void)delegateMethod2 {
[someClass sendData:self.data];
}
Now, this works fine sometimes but the other times, delegateMethod2 gets called before delegateMethod1.
I need to know how to manage this elegantly so that the line: [someClass sendData:self.data]; gets called only when both delegateMethod1 and delegateMethod2 have been called.
I know I can do it by using a variable to set to something on each delegate call but there has to be an elegant way to do this.
Any help?
Remembering which delegate has been called seems the easiest and cleanest solution to me.
But you can make it symmetric by moving the check to a separate method, so that
is does not matter which delegate is called first:
- (void)checkIfDataCanBeSent {
if (self.method1called && self.method2called) {
[someClass sendData:self.data];
}
}
- (void)delegateMethod1:(id)data {
self.method1called = YES;
// ...
[self checkIfDataCanBeSent];
}
- (void)delegateMethod2 {
self.method2called = YES;
// ...
[self checkIfDataCanBeSent];
}
(I have assumed that all delegate methods are called on the main thread, otherwise
one would have to add some synchronization.)
I believe, using a indicative variable to be the most elegant way to get over this. But this variable has to be kept in the delegate caller object.
Pseudo-type explanation
#interface DelegateCaller
{
BOOL hasCalled1stMethod;
}
#property(nonatomic,weak) id delegate;
#end
#implementation DelegateCaller
-(void)in_some_process_1
{
[self.delegate delegateMethod1]; //call
hasCalled1stMethod = YES; //set indicator
}
-(void)in_some_process_2
{
if(hasCalled1stMethod)
{
[self.delegate delegateMethod2]; //call
hasCalled1stMethod = NO; //reset indicator for reuse, if required.
}
}
#end
This way you'll not have to maintain any variable in the delegate itself, because the regulation of calling is maintained in the caller-object itself.
Another case:
If the delegateMethod1 is called from some object1 and the delegateMethod2 is called from some other object2, then again the indicative variable method is the most elegant way (in this limited scenario)
Pseudo-type explanation:
#interface ClassDelegateObject //aka the callee
{
BOOL hasCalledMethod1;
}
#end
#implementation ClassDelegateObject
-(void)delegateMethod1:(NSData*)data
{
self.data = data;
hasCalledMethod1 = YES; //set the indicator.
}
-(void)delegateMethod2
{
//here relying on the self.data!=nil will not be fruitful
//in case the self.data is not nil and hold some previous garbage data then
//this logic will fail.
if(hasCalledMethod1)
{
[someClass sendData:self.data];
hasCalledMethod1 = NO; //reset the variable for reuse if required.
}
}
#end
I would suggest that you rethink how the code works. Maybe you can check if there is no data and if so send it once it is ready:
- (void)delegateMethod1:(id)data {
self.data = data;
if (self.dataShouldBeSentWhenReady) {
[self sendData];
}
}
- (void)delegateMethod2 {
if (self.data) {
[self sendData];
} else {
[self setDataShouldBeSentWhenReady:YES];
}
}
- (void)sendData {
[self setDataShouldBeSentWhenReady:NO];
[someClass sendData:self.data];
}
I'm following the Stanford course, and we had to build a method for the app that checks for 2 cards matching, this is how the model that have the logic looks like (the method to look there is flipCardAtIndex):
#import "CardMatchingGame.h"
#import "PlayingCardsDeck.h"
#interface CardMatchingGame()
#property (readwrite, nonatomic) int score;
#property (strong, nonatomic) NSMutableArray *cards;
#property (strong, nonatomic) NSString *notification;
#end
#implementation CardMatchingGame
-(NSMutableArray *) cards {
if (!_cards) _cards = [[NSMutableArray alloc] init];
return _cards;
}
-(id)initWithCardCount:(NSUInteger)count usingDeck:(Deck *)deck {
self = [super init];
if (self) {
for (int i = 0; i < count; i++) {
Card *card = [deck drawRandonCard];
if (!card) {
self = nil;
} else {
self.cards[i] = card;
}
}
}
return self;
}
-(Card *) cardAtIndex:(NSUInteger)index {
return (index < self.cards.count) ? self.cards[index] : nil;
}
#define FLIP_COST 1
#define MISMATCH_PENALTY 2
#define BONUS 4
-(void) flipCardAtIndex:(NSUInteger)index {
Card *card = [self cardAtIndex:index];
if (!card.isUnplayable) {
if (!card.isFaceUp) {
for (Card *otherCard in self.cards) {
if (otherCard.isFaceUp && !otherCard.isUnplayable) {
int matchScore = [card match:#[otherCard]];
if (matchScore) {
otherCard.unplayble = YES;
card.unplayble = YES;
self.notification = [NSString stringWithFormat:#"%# & %# match!", card.contents, otherCard.contents];
self.score += matchScore * BONUS;
} else {
otherCard.faceUp = NO;
self.score -= MISMATCH_PENALTY;
self.notification = [NSString stringWithFormat:#"%# did not matched to %#", card.contents, otherCard.contents];
}
break;
}
}
self.score -= FLIP_COST;
}
card.faceUp = !card.isFaceUp;
}
}
#end
And this is the class model of the whole game, that got the actual matching method:
#import "PlayingCards.h"
#implementation PlayingCards
#synthesize suit = _suit;
//overriding the :match method of cards to give different acore if its only a suit match or a number match
-(int)match:(NSArray *)cardToMatch {
int score = 0;
if (cardToMatch.count == 1) {
PlayingCards *aCard = [cardToMatch lastObject];
if ([aCard.suit isEqualToString: self.suit]) {
score = 1;
} else if (aCard.rank == self.rank) {
score = 4;
}
}
return score;
}
//more stuff...
W already created it with an array so we will be able to extend it for more objects, but now i'm trying to figure out how do I extend it :/
This is my github for the project https://github.com/NirOhayon/Matchismo
i'm new to objective C and would appreciate it munch if you could help me to figure it out.
Thanks a bunch
You can chain these with a loop to check them all. Very basic way of doing it. Just loop through each card and check it against the "self" card that you have and increment the score instead of setting it.
-(int)match:(NSArray *)cardToMatch {
int score = 0;
for(int i = 0; i < cardToMatch.count; i++) {
PlayingCards *aCard = cardToMatch[i];
if ([aCard.suit isEqualToString: self.suit]) {
score += 1;
} else if (aCard.rank == self.rank) {
score += 4;
}
}
return score;
}
For flipCardAtIndex: , I would change it to flipCardsAtIndexes:(NSArray*)indexes, where indexes is an NSArray of NSNumbers. Then I would run a for loop checking and removing any cards that are unplayable or faceup, and pass through the remaining cards at those indexes to check match, and retrieve the match score.
To tell your view controller to add another card depends on how you have your view controller set up. You could do a protocol in a method that your view controller becomes the delegate of, and through a protocol method, tell it to switch. It could also be simpler than that, depending on how it checks your model of cards to decide what to show, if it sees three cards available instead of two, it could switch.
As the point of this exercise is to learn iOS programming, I want to give you a good head start and you should tweak and figure some stuff out on your own. I have a feeling you're a novice at programming, and if you are, you'll be surprised how much programming at your stage is trial and error. Eventually it will become second nature.
I am developing an Objective-C application, and what I want to do, is something like the following:
+-----------------+ +---------------+
| Some Object | <---------- | Synchronize |
|(Not Thread Safe)| | Proxy |
+-----------------+ / +---------------+
/
/ Intercepts [someobject getCount]
/ #synchronize (someObject)
/
[someObject getCount] /
+----------------------+
| Some Calling Object |
+----------------------+
What I've asking is, how can I create an object in objective-c, that intercepts messages sent to another object, in order to perform code before the message is sent to that object.
Some things that I think will not work:
Categories (I need this to only happen for certain instances of a class)
Rewriting the object (I don't have access to the source of the object)
Method swizzling (once again, this need to only happen for certain instances of a class)
You would implement an NSProxy that forwards messages to your non-thread-safe object.
Here is a nice writeup of message forwarding in Objective-C, and here is Apple's documentation.
To handle thread safety, it depends on what you need. If your non-thread-safe object must run on a specific thread then you can use a NSRunLoop on said thread to serialize messages to that object.
Here is an example of using NSInvocation in conjunction with NSRunLoop. In that example they're using performSelector:withObject:afterDelay: but to use it with performSelector:onThread:withObject:waitUntilDone: would be very similar.
Otherwise, just use a single NSRecursiveLock in your proxy.
If you know exactly what instances should have the behavior you are trying to achieve you can go with method swizzling and call the base implementation if the instance is not the one you are looking for.
You can have a global shared object that lists the "interesting" instances and use it in the swizzling implementation whether you have to call the base one or your custom one.
So, I bit the bullet, and decided to make my own proxy class. To subclass, you simply override the 'forwardInvocation:' message, and you call any code you need there, before calling [super forwardInvocation:]. Please not this will NOT work with vardic methods, as NSInvocation doesn't work with vardic methods.
#import <Foundation/Foundation.h>
#import <objc/runtime.h>
#import <objc/objc.h>
#import <objc/message.h>
#interface RJProxy : NSObject {
#private
NSObject *target;
}
#property(readwrite, retain) NSObject *target;
-(NSObject *) getTarget;
#end
#implementation RJProxy
#synthesize target;
-(NSMethodSignature *) methodSignatureForSelector:(SEL)aSelector
{
if (objc_getAssociatedObject(self, "isProxy"))
{
IMP NSObjectImp = [NSObject instanceMethodForSelector:#selector(methodSignatureForSelector:)];
NSMethodSignature *methodSignature = (NSMethodSignature *) NSObjectImp(self, #selector(methodSignatureForSelector:), aSelector);
if (methodSignature)
return methodSignature;
return [target methodSignatureForSelector:aSelector];
}
else
{
Class subClass = self->isa;
#try {
self->isa = objc_getAssociatedObject(self, "realSuperclass");
return [super methodSignatureForSelector:aSelector];
}
#finally {
self->isa = subClass;
}
}
}
-(void) forwardInvocation:(NSInvocation *)anInvocation
{
if (objc_getAssociatedObject(self, "isProxy"))
{
Class subClass = target->isa;
target->isa = objc_getAssociatedObject(self, "realSuperclass");
[anInvocation invokeWithTarget:target];
target->isa = subClass;
}
else
{
Class realSuperclass = objc_getAssociatedObject(self, "realSuperclass");
Class subclass = self->isa;
self->isa = realSuperclass;
if ([self respondsToSelector:[anInvocation selector]])
{
[anInvocation invokeWithTarget:self];
}
else
{
[self doesNotRecognizeSelector:[anInvocation selector]];
}
self->isa = subclass;
}
}
-(NSObject *) getTarget
{
if (objc_getAssociatedObject(self, "isProxy"))
{
return target;
}
return self;
}
#end
BOOL object_setProxy(NSObject *object, RJProxy *proxy);
BOOL object_setProxy(NSObject *object, RJProxy *proxy)
{
proxy.target = object;
Class objectClass = object_getClass(object);
Class objectSub = objc_allocateClassPair(objectClass, [[NSString stringWithFormat:#"%s_sub%i", class_getName(objectClass), objc_getAssociatedObject(objectClass, "subclassTimes")] UTF8String], 0);
objc_setAssociatedObject(objectClass, "subclassTimes", (id) ((int) objc_getAssociatedObject(objectClass, "subclassTimes") + 1), OBJC_ASSOCIATION_ASSIGN);
objc_registerClassPair(objectSub);
Class proxyClass = object_getClass(proxy);
Class proxySub = objc_allocateClassPair(proxyClass, [[NSString stringWithFormat:#"%s_sub%i", class_getName(proxyClass), objc_getAssociatedObject(proxyClass, "subclassTimes")] UTF8String], 0);
objc_setAssociatedObject(proxyClass, "subclassTimes", (id) ((int) objc_getAssociatedObject(proxyClass, "subclassTimes") + 1), OBJC_ASSOCIATION_ASSIGN);
objc_registerClassPair(proxySub);
object_setClass(object, proxySub);
object_setClass(proxy, proxySub);
objc_setAssociatedObject(object, "isProxy", (id) NO, OBJC_ASSOCIATION_ASSIGN);
objc_setAssociatedObject(proxy, "isProxy", (id) YES, OBJC_ASSOCIATION_ASSIGN);
objc_setAssociatedObject(object, "realSuperclass", objectClass, OBJC_ASSOCIATION_ASSIGN);
objc_setAssociatedObject(proxy, "realSuperclass", proxyClass, OBJC_ASSOCIATION_ASSIGN);
return NO;
}
#interface SynchronizeProxy : RJProxy
#end
#implementation SynchronizeProxy
-(void) forwardInvocation:(NSInvocation *)anInvocation {
#synchronized ([self getTarget])
{
[super forwardInvocation:anInvocation];
}
}
#end
int main (int argc, const char * argv[])
{
#autoreleasepool {
NSArray *arrayToSynchronize = [NSArray arrayWithObjects:#"This, is, a, test!", nil];
SynchronizeProxy *myProxy = [SynchronizeProxy new];
object_setProxy(arrayToSynchronize, myProxy);
// now all calls will be synchronized!
NSLog(#"Array at address 0x%X with count of %lu, and Objects %# ", (unsigned) arrayToSynchronize, [arrayToSynchronize count], arrayToSynchronize);
[myProxy release];
[arrayToSynchronize release];
}
return 0;
}
I know that in order to show/hide the throbber on the status bar I can use
[UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
[UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
But my program sends comm requests from many threads, and I need a location to control whether the throbber should be shown or hidden.
I thought about a centralized class where every comm request will register and this class will know if one-or-many requests are currently transferring bytes, and will turn the throbber on, otherwise - off.
Is this the way to go? why haven't Apple made the throbber appear automatically when networking is happening
Try to use something like this:
static NSInteger __LoadingObjectsCount = 0;
#interface NSObject(LoadingObjects)
+ (void)startLoad;
+ (void)stopLoad;
+ (void)updateLoadCountWithDelta:(NSInteger)countDelta;
#end
#implementation NSObject(LoadingObjects)
+ (void)startLoad {
[self updateLoadCountWithDelta:1];
}
+ (void)stopLoad {
[self updateLoadCountWithDelta:-1];
}
+ (void)updateLoadCountWithDelta:(NSInteger)countDelta {
#synchronized(self) {
__LoadingObjectsCount += countDelta;
__LoadingObjectsCount = (__LoadingObjectsCount < 0) ? 0 : __LoadingObjectsCount ;
[UIApplication sharedApplication].networkActivityIndicatorVisible = __LoadingObjectsCount > 0;
}
}
UPDATE: Made it thread safe
Having some logic in your UIApplication subclass singleton seems like the natural way to handle this.
//#property bool networkThingerShouldBeThrobbingOrWhatever;
// other necessary properties, like timers
- (void)someNetworkActivityHappened {
// set a timer or something
}
- (void)networkHasBeenQuietForABit
// turn off the indicator.
// UIApplcation.sharedApplication.networkActivityIndicatorVisible = NO;
}
EDIT: It was suggested to me that I implement the strategy pattern (http://en.wikipedia.org/wiki/Strategy_pattern), which I think I would do as several objects that implement a delegate protocol in Objective-C. This accomplishes the encapsulation I want while still allowing me to have a generic view controller in memory.
I have a class called DetailViewController that displays information about various types of data - waypoints, trails, maps, photos.
Right now, this class is 1400 lines long and it has some messy switch statements. For example:
- (void) changeMiniView:(id)sender {
if (self.track) {
[self changeTrackMiniView:[sender selectedSegmentIndex]];
} else if (self.waypoint) {
[self changeWaypointMiniView:[sender selectedSegmentIndex]];
} else if (self.photo) {
[self changePhotoMiniView:[sender selectedSegmentIndex]];
} else if (self.map) {
[self changeMapMiniView:[sender selectedSegmentIndex]];
}
}
This would be a lot neater if I made subclasses of DetailViewController, but my conundrum is I would like to keep the viewController in memory and just change certain elements, so I can have crisp transitions, particularly on 3G phones.
I feel like if I want my code to be neat, I have to take a performance hit.
Have the current view in a field in your object (rather than one field for every type of miniview you have), and implement changeMiniView for each of them.
Then your method would look like:
- (void) changeMiniView: (id)sender {
[self.currentMiniView changeMiniView: [sender selectedSegmentIndex]];
}
How about using selector?
- (void)viewDidLoad {
if (self.track) {
sel = #selector(changeTrackMiniView:);
} else if (self.waypoint) {
sel = #selector(changeWaypointMiniView:);
} else if (self.photo) {
sel = #selector(changePhotoMiniView:);
} else if (self.map) {
sel = #selector(changeMapMiniView:);
}
}
- (void)changeTrackMiniView:(id)sender {
....
}
- (void)changeMiniView:(id)sender {
[self performSelector:sel withObject:sender];
}