UPDATE 8/17/16

If you want to remove local AND server data, all you have to do is call the delete method from your MSSyncTable.
It sends a request to your local data source to remove the given item, then queues a request to send the delete
to the mobile service.

It first removes the data locally.
Then, when the queued request goes through into the mobile service, then it will update remotely,
and you can log into your Azure account, look at the Easy Tables, and see that the item has been removed.

/// Sends a request to the MSSyncContext's data source to delete the given

/// item in the local store. In addition QUEUES a request to send the delete

/// to the mobile service.

[self.syncTable delete:item completion:^(NSError * _Nullable error) {

if(error) {

NSLog(@"ERROR %@", error);

} else {

NSLog(@"DELETED LOCALLY!");

dispatch_async(dispatch_get_main_queue(), completion);

}

}]; //delete

Let’s say you have added 4 entries:

The database reflects this:

Then, let’s say there is a direct deletion in the DB. The item we deleted it is has id A24D9651-A252-4A70-81A8-61520BB5C0D1

Now, even though this is not the way Microsoft wants us to do deletion, we do need a way to sync our local DB with the server DB just in case this happens.

Open the project. Let’s implement a log method to display the data in our local db.

QSAppDelegate.h

1	-(void)logAllTodoItem;

The logging is to verify correctness of local db. It is also used to get the id of users you want to delete.

For example, on the server side, if someone deletes Ivan, and in case you forgot to safe the ID, you can always use the log method to display the local results:

2 — text = Ivan, id = 46206A2F-26A7-4667-8A8E-391CA51EE731

QSAppDelegate.m

-(void)logAllTodoItem {

NSLog(@"%s - logAllTodoItem method called", __FUNCTION__);

//Get all the projects in the data store

NSFetchRequest * request = [[NSFetchRequest alloc] init];

NSEntityDescription * entity = [NSEntityDescription entityForName:@"TodoItem"

inManagedObjectContext:self.managedObjectContext];

request.entity = entity;

//use performBlock if your self.mainQueueContext is a Private Concurrent Queue

//[self.mainQueueContext performBlock:^{

//use it like this if your mainQueueContext is of Private MAIN Queue, which updates the UI

NSArray * list = [self.managedObjectContext executeFetchRequest:request error:nil];

//List out contents of each project

if( [list count] == 0 ) {

NSLog(@"%s - There are no Events in the data store yet", __FUNCTION__);

}

else {

NSLog(@"------------ RESULTS FROM DATABASE ------------");

NSLog(@"%lu", (unsigned long)[list count]);

[list enumerateObjectsUsingBlock:^(id _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {

NSLog(@"%lu --- text = %@, id = %@",

(unsigned long)idx,

[obj valueForKey:@"text"],

[obj valueForKey:@"id"]);

}];

}

Delete – server and local

Then, let’s write the delete method for the service, so that we can remove the server data, and the local data.

Notice that we use MSTable’s deleteWithId to remove the item from the server.

We use MSSyncTable’s delete:item to remove item locally.

QSTodoService.h

1 2	- (void)deleteItem:(NSDictionary *)item completion:(QSCompletionBlock)completion;

QSTodoService.m

//mark the delete column to true

- (void)deleteItem:(NSDictionary *)item

completion:(QSCompletionBlock)completion {

//get the entity's id

NSString * rowId = (NSString*)[item objectForKey:@"id"];

//get the Easy Table name on server

MSTable *itemTable = [self.client tableWithName:@"TodoItem"];

//tell this table to delete the entity with specified ID

[itemTable deleteWithId: rowId

completion:^(id _Nullable itemId, NSError * _Nullable error) {

if(!error) {

NSLog(@"DELETED IN SERVER");

}

//LOCAL DELETE

[self.syncTable delete:item completion:^(NSError * _Nullable error) {

if(error) {

NSLog(@"ERROR %@", error);

} else {

NSLog(@"DELETED LOCALLY!");

dispatch_async(dispatch_get_main_queue(), completion);

}

}]; //delete

}]; //deleteWithId

}

Now, given an ID, let’s check to see if the server has that ID. Insert the ID of the item you just deleted (A24D9651-A252-4A70-81A8-61520BB5C0D1) into rowId.

For matching local data wit direct delete in the server DB, we simply use local delete.

-(void)checkServerDeletionCompletion:(QSCompletionBlock)completion {

//you can do this periodically

//for example, if read your local data, and want to check if an id still exist in the server

NSString * rowId = [NSString stringWithFormat:@"A24D9651-A252-4A70-81A8-61520BB5C0D1"];

//get the Easy Table name on server

MSTable *itemTable = [self.client tableWithName:@"TodoItem"];

[itemTable readWithId:rowId completion:^(NSDictionary * _Nullable item, NSError * _Nullable error) {

if(!error) {

NSLog(@"%@", item);

} else {

NSLog(@"%@", error);

NSDictionary * toDelete = [NSDictionary dictionaryWithObjectsAndKeys:rowId, @"id", nil];

[self.syncTable delete:toDelete completion:^(NSError * _Nullable error) {

if(error) {

NSLog(@"ERROR %@", error);

} else {

NSLog(@"DELETED LOCALLY!");

dispatch_async(dispatch_get_main_queue(), completion);

}

}];

}

}];

}

For simplicity purposes, we’ll just do the logging, and checking in refresh method of QSTodoListViewController:

- (void) refresh

{

QSAppDelegate *appDelegate = (QSAppDelegate *)[[UIApplication sharedApplication] delegate];

[appDelegate logAllTodoItem];

[self.todoService checkServerDeletionCompletion:^{

QSAppDelegate *appDelegate = (QSAppDelegate *)[[UIApplication sharedApplication] delegate];

[appDelegate logAllTodoItem];

}];

[self.refreshControl beginRefreshing];

[self.todoService syncData:^

{

[self.refreshControl endRefreshing];

}];

}

Run the program…first you’ll see the logging to prove that your local database is out of sync with the server database:

2016-08-16 16:19:42.297 EpamEvents[4441:456591] -[QSAppDelegate logAllTodoItem] – logAllTodoItem method called
2016-08-16 16:19:42.297 EpamEvents[4441:456591] ———— RESULTS FROM DATABASE ————
2016-08-16 16:19:42.298 EpamEvents[4441:456591] 4
2016-08-16 16:19:42.298 EpamEvents[4441:456591] 0 — text = Dean, id = 1D9AB54C-793A-4240-A8FB-3E968BB16D09
2016-08-16 16:19:42.298 EpamEvents[4441:456591] 1 — text = Ricky, id = A24D9651-A252-4A70-81A8-61520BB5C0D1
2016-08-16 16:19:42.298 EpamEvents[4441:456591] 2 — text = Ralph, id = 49E6A521-CB9D-4D37-9CEB-F81403707202
2016-08-16 16:19:42.299 EpamEvents[4441:456591] 3 — text = Ivan, id = 46206A2F-26A7-4667-8A8E-391CA51EE731

Then, when you run through the method, you will see the checkServerDeletionCompletion method call readWithId. First it checks for item (A24D9651-A252-4A70-81A8-61520BB5C0D1). Remember, someone has mistakenly deleted this item from the DB directly, hence you’ll get an error warning like so:

2016-08-16 16:20:06.084 EpamEvents[4441:456591] Error Domain=com.Microsoft.MicrosoftAzureMobile.ErrorDomain Code=-1302 “The item does not exist” UserInfo={NSLocalizedDescription=The item does not exist, com.Microsoft.MicrosoftAzureMobile.ErrorRequestKey= { URL: https://epamevents.azurewebsites.net/tables/TodoItem/A24D9651-A252-4A70-81A8-61520BB5C0D1 }, com.Microsoft.MicrosoftAzureMobile.ErrorResponseKey= { URL: https://epamevents.azurewebsites.net/tables/TodoItem/A24D9651-A252-4A70-81A8-61520BB5C0D1 } { status code: 404, headers {
“Cache-Control” = “no-cache”;
“Content-Length” = 35;
“Content-Type” = “application/json; charset=utf-8”;
Date = “Tue, 16 Aug 2016 08:19:58 GMT”;
Etag = “W/\”23-xvKyQMaUWUD9x7DI0LISBQ\””;
Expires = 0;
Pragma = “no-cache”;
Server = “Microsoft-IIS/8.0”;
“Set-Cookie” = “ARRAffinity=871fe01e072348697c5ee601ae1b8377c6473f1f3b3bb965170b664f5c32221d;Path=/;Domain=epamevents.azurewebsites.net”;
“X-Powered-By” = “Express, ASP.NET”;
} }}

Then once the error is noticed, we delete it from our local via the delete method. As you can see, locally, Ricky has been deleted.

The result is:

2016-08-16 16:20:06.091 EpamEvents[4441:457812] DELETED LOCALLY!
2016-08-16 16:20:09.886 EpamEvents[4441:456591] -[QSAppDelegate logAllTodoItem] – logAllTodoItem method called
2016-08-16 16:20:09.887 EpamEvents[4441:456591] ———— RESULTS FROM DATABASE ————
2016-08-16 16:20:09.887 EpamEvents[4441:456591] 3
2016-08-16 16:20:09.887 EpamEvents[4441:456591] 0 — text = Dean, id = 1D9AB54C-793A-4240-A8FB-3E968BB16D09
2016-08-16 16:20:09.888 EpamEvents[4441:456591] 1 — text = Ralph, id = 49E6A521-CB9D-4D37-9CEB-F81403707202
2016-08-16 16:20:09.888 EpamEvents[4441:456591] 2 — text = Ivan, id = 46206A2F-26A7-4667-8A8E-391CA51EE731

_cmd

August 15, 2016C/C++/Objective-Cadmin

http://stackoverflow.com/questions/4418233/cmd-value-inside-c-functions

The first two parameters passed to all Objective-C methods are self and _cmd, then whatever other arguments the actual method takes.

-(void)erase {

NSLog(@"%@", NSStringFromSelector(_cmd));

}

How to load profile info

August 10, 2016iOS, Projectsadmin

Declare the header file for EpamAuth:

1	#import "EpamAuth.h"

Then declare a property that conforms to the Authorization interface.

@interface ViewController ()

{

}

@property (nonatomic, strong) id <Authorization> auth;

@end

Then initialize the property in init or a lazyloading accessor

1	self.auth = [EpamAuth defaultAutho];

Finally, use it like this:

[self.auth loginAndGetProfileDataForController:self

withCompletion:^(NSError *error, NSDictionary * profile) {

if(!error && profile) {

NSLog(@"%@", [profile objectForKey:@"city"]);

NSLog(@"%@", [profile objectForKey:@"country"]);

NSLog(@"%@", [profile objectForKey:@"department"]);

NSLog(@"%@", [profile objectForKey:@"jobTitle"]);

NSLog(@"%@", [profile objectForKey:@"givenName"]);

NSLog(@"%@", [profile objectForKey:@"mail"]);

NSLog(@"%@", [profile objectForKey:@"telephoneNumber"]);

NSLog(@"%@", [profile objectForKey:@"usageLocation"]);

NSLog(@"%@", [profile objectForKey:@"userPrincipalName"]);

}

}];

If its your first time logging in, you will have a login window appear. Sign in using your EPAM credentials.

If you have previously logged in, your authentication token will be saved in the keychain, and you don’t have to log in a second time. You simply will be automatically logged in.

To log out:

//log out the current user

[self.auth logoutWithCompletion:^(NSError *error) {

NSLog(@"logged out");

}];

Protected: Download async images into your table

August 9, 2016iOS, Projectsadmin

Binary Search Tree part 2

August 6, 2016Uncategorizedadmin

height of the tree

int MyBST::height(Node * node) {

if(node== NULL) {

return 0;

}

else {

cout << "...on node : " << node->data << endl;

//first we get the height of the left

int leftHeight = height(node->left);

int rightHeight = height(node->right);

//which everone is larger gets added?

if((node->right) == NULL && (node->left == NULL)) return 0; //if its a leaf, its a 0

else {

if(leftHeight > rightHeight) return (leftHeight + 1);

else return (rightHeight + 1);

}

Loose Coupling through Dependency Injection

August 3, 2016C/C++/Objective-Cdesign patternadmin

https://yalantis.com/blog/dependency-injection-di-service-locator/
http://stackoverflow.com/questions/3058/what-is-inversion-of-control

In case the link does not work, the article can be downloaded and opened from your local machine here

Dependency Injection

Interface Injection

The Problem

follow along with the code in Dependency Injection

Say you have a MovieLister object that has a method moviesDirectedByDirector. It uses a class called TextFileMovieFinder in order to call methods on it and get return values for the results.

This is the simplest solution, but yet, it creates tight-coupling because the method full depends on the exact implementation of TestFileMovieFinder.

- (NSArray *)moviesDirectedByDirector:(NSString *)director {

// 1)

// What is Finder and where it came from?

// We need to have Finder inside the method to get the list of the movies.

// How can we get the Finder inside the method?

// The simplest and wrong solution is to create the required object inside the method.

// In this case the method (moviesDirectedByDirector) fully depends on the exact implementation

// of the exact class TestFileMovieFinder.

TextFileMovieFinder * finder = [[TextFileMovieFinder alloc] initWithTextFileName:@"movies.txt"];

NSArray *allMovies = [finder findAllMovies];

NSMutableArray *result = [NSMutableArray array];

for (Movie * movie in allMovies) {

if ([movie.director isEqualToString:director]) {

[result addObject:movie];

}

return result;

Implementing a protocol and using delegate for loose coupling

In the MovieLister, our job is to list. We just need to connect it to a movie finder that gives us the results.

We do this by having a delegate that points to any object that conforms to MovieFinder.
That way, we don’t care what that object does, just give us the result via the protocol MovieFinder’s

1	- (NSArray *)findAllMovies;

@interface MovieLister : NSObject

{

}

//Whatever object that implements the MovieFinder protocol

//hold onto the movie finder object

@property (nonatomic, strong) id <MovieFinder> finder;

@end

..and you use it like so:

- (NSArray *)moviesDirectedByDirector:(NSString *)director {

NSArray * allMovies = [self.finder findAllMovies];

NSMutableArray *result = [NSMutableArray array];

for (Movie * movie in allMovies) {

if ([movie.director isEqualToString:director]) {

[result addObject:movie];

}

return result;

}

Now, let’s update our TextFileMovieFinder object so that it conforms to the MovieFinder protocol.

TextFileMovieFinder.h

@protocol MovieFinder <NSObject>

- (NSArray *)findAllMovies;

@end

@interface TextFileMovieFinder : NSObject <MovieFinder>

{

}

TextFileMovieFinder.m

#import "TextFileMovieFinder.h"

@interface TextFileMovieFinder ()

{

}

@property(nonatomic, strong) NSString * fileName;

@end

@implementation TextFileMovieFinder

- (id)initWithTextFileName:(NSString *)textFileName {

if(self=[super init]) {

self.fileName = textFileName;

}

return self;

}

#pragma mark MovieFinder

- (NSArray *)findAllMovies {

return [NSArray arrayWithObjects:

@"Saving Private Ryan",

@"Old Boy",

@"The Karate Kid",

@"Matrix",

nil];

}

But how do we connect them?

1) Constructor Injection

1 2	TextFileMovieFinder * finder = [[TextFileMovieFinder alloc] initWithTextFileName:@"movies.txt"]; MovieLister * lister = [[MovieLister alloc] initWithMovieFinder:finder];

Constructor injection is perfect for “obligatory” dependencies, without which the class can’t implement its task. This way we locate all the dependencies in one place – in the constructor. When the class expands and starts using additional services, they will appear in the constructor as parameters which cannot be left unnoticed. So when another parameter is added to the constructor and the number of all the parameters becomes higher than 4, you need to think about the architecture of your class.

2) Setter Injection

TextFileMovieFinder * finder = [[TextFileMovieFinder alloc] initWithTextFileName:@"movies.txt"];

MovieLister * lister = [[MovieLister alloc] init];

[lister setFinder:finder];

Setter injection (property injection) fits “optional” dependencies, those which have a reasonable implementation known to the class by default. At the same time there has to be a possibility to change the dependency while the class is working and without any negative consequences.

Delegates

http://stackoverflow.com/questions/7052926/what-is-the-purpose-of-an-ios-delegate

The advantage of the delegate design pattern is loose coupling. It enables class A (the delegate) to depend on class B (the delegating class) without class B having to have any knowledge of class A. This ensures that the dependency relationship is one-way only, rather than being circular.

It also forms the foundation (lower case “f”) of Apple’s frameworks because it allows them to invoke your code as appropriate when functionality specific to your application is required. For example, responding to a button tap or telling a table view how many sections there should be.

Protected: Block Storage on Azure using iOS

August 3, 2016iOSAzureadmin

Adding and Removing Observer in UIView

July 26, 2016iOSadmin

ref – http://stackoverflow.com/questions/8200775/when-to-unsubscribe-from-a-nsnotification-in-a-uiview

In your UIView custom class:

- (void)didMoveToWindow {

if (self.window) {

NSLog(@"Added to a window, similar to -viewDidLoad.");

// Subscribe to notifications here.

[[NSNotificationCenter defaultCenter] addObserver:self

selector:@selector(topicAndEntry:)

name:INSERT_TOPIC_ENTRY

object:nil];

[[NSNotificationCenter defaultCenter] addObserver:self

selector:@selector(topicAndEntry:)

name:INSERT_REQUIRED_KEY_VALUE

object:nil];

}

- (void)willMoveToWindow:(UIWindow *)newWindow {

if (newWindow == nil) {

NSLog(@"Will be removed from window, similar to -viewDidUnload.");

// Unsubscribe from any notifications here.

[[NSNotificationCenter defaultCenter] removeObserver:self

name:INSERT_TOPIC_ENTRY

object:nil];

[[NSNotificationCenter defaultCenter] removeObserver:self

name:INSERT_REQUIRED_KEY_VALUE

object:nil];

}

Protected: from data structure to JSON and back in iOS

July 23, 2016C/C++/Objective-C, iOSJSONadmin

Why use hex to represent memory address locations in Programming

July 23, 2016C/C++/Objective-Cadmin

https://learn.sparkfun.com/tutorials/hexadecimal
http://stackoverflow.com/questions/14113051/how-to-calculate-size-of-memory-by-given-a-range-of-address

The hexadecimal system is commonly used by programmers to describe locations in memory because:

1) it can represent every byte (i.e., eight bits) as two consecutive hexadecimal digits instead of the eight digits that would be required by binary (i.e., base 2) numbers

BINARY
_ _ _ _ _ _ _ _ = 8 bits = 1 byte.

2 2 2 2 2 2 2 2 = 2^8 = 256 representations (memory addresses)

HEX
_ _ where each bit has 16 representations (0-9, a-f) so
16 16 = 16 ^ 2 = 256 representations (memory addresses)

2) and the three digits that would be required with decimal numbers.

example

_ _ _ _ _ _ _ _ ( 8 bits )

0 0 0 0 0 0 0 0 ( 1 )
0 0 0 0 0 0 1 1 ( 2^1 + 2^0 = 3 )
0 0 0 0 1 0 1 0 ( 2^3 + 2^1 = 8 + 2 = 10 )
1 1 1 1 1 1 1 1 ( 2^7 + 2^6 + 2^5 + 2^4 + 2^3 + 2^2 + 2^1 + 2^0 = 128 + 64 + 32 + 16 + 8 + 4 + 2 + 1 = 255

where each number represent a memory location.

Hence, 8 bits we can represent from from 0 – 255, or 256 different memory locations.

However, the 8 bit representation is difficult visually.

The hex system can represent 256 memory addresses with just 2 hex digits.

0 0 ( 0 )
0 3 ( 3 )
0 10 ( 10 )
F A ( 15 * 16^1 + 10 * 16^0 = 240 + 10 = 250 )
F F ( 15 * 16^1 + 15 * 16^0 = 255 )

In addition, it is much easier for humans to read hexadecimal numbers than binary numbers, and it is not much more difficult for computer professionals to read hexadecimal numbers than decimal numbers.

Converting from Decimal to Hex

Say we want to convert 61453 to hex.

61352/16 = 3840 R13 (13 in hex is D)
3840 /16 = 240 R0 (0 in hex is 0)
240 /16 = 15 R0 (0 in hex is 0)
15 /16 = 0 R15 (15 in hex is F)

Hence the resulting conversion to hex is 0xF00D

Converting from Hex to Decimal

0xF00D

F * 16^3 + 0 * 16^2 + 0 * 16^1 + D * 16^0
15 * 4096 + 0 * 256 + 0 * 16 + 13 * 1 = 61440 + 0 + 0 + 13 = 61453

Binary to Hex

We use hex in electrical and computer engineering because it’s incredibly easy to convert to and from binary – the 1’s and 0’s language of computers.

each digit of a hexadecimal number “maps” to four bits (a bit being an individual binary digit) of a binary value.

a hex decimal is: 0-15, which is 16 digits. 16 representations.

In binary, we need 4 bits to make 16 representations:

0000 = 0
1111 = 15

Hence that is how ONE hex bit “maps” to FOUR binary bits.

Going further a byte – eight binary digits – can be represented by two hexadecimal digits.
This makes hex a really great, concise way to represent a byte or group of bytes.

From binary to hex

binary: 0b101111010100001

sort them into group of 4s:

0101 1110 1010 0001
5 E A 1

From hex to binary

Take a hex digit and turn it into four binary digits:

0 x B E E F

B is 11
11 in binary is 1 0 1 1

E is 14
14 in binary is 1 1 1 0

F is 15
15 in binary is 1 1 1 1

Hence 0 x BEEF in binary is

1011 1110 1110 1111

Easily representing values of bytes

Hex is often easier for us to work with because the values are shorter and more memorable than a long string of 1’s and 0’s.

Let’s say:

CTRL_REG2_G is the name of the register, with address 0010 0001

it’s much easier to remember 0x21 than 0b010001
For that reason, we’re much more likely to use hex values in our code than their binary equivalents.

Working with programming languages in IDE

Often in IDEs, when you are debugging, you’ll see hex addresses assigned to your variables.

For example, say you create an array:

1	int * entry = new int[8];

If you print out the addresses of each integer, you

cout << entry << endl;

cout << (entry + 1) << endl;

cout << (entry + 2) << endl;

for ( int i = 0; i < 8;i i++) {

cout << (entry +i) << endl;

}

you’ll see the list of addresses for each integer

entry[0]: 0

address 0x1004000a0

entry[1]: 1

address 0x1004000a4

entry[2]: 2

address 0x1004000a8

entry[3]: 3

address 0x1004000ac

entry[4]: 4

address 0x1004000b0

entry[5]: 5

address 0x1004000b4

entry[6]: 6

address 0x1004000b8

entry[7]: 7

address 0x1004000bc

Given that we created an array of 8 integer elements,
each int can represent up to 4 bytes (or 4 * 8 bits = 2^32 bits) of data.

This means each integer can have 2^32 representations.

For example,
-2,147,483,648 to 2,147,483,647 as a signed int (signed means negative and positive)
or 0 to 4294967296 as an unsigned int.

We see that the 1st int’s starting address is at 0x1004000a0.
the 2nd int’s starting address is at 0x1004000a4.

So how does an int sit at 0x1004000a0 to 0x1004000a4-1, and to mean 4 bytes?

Most CPU has the 1 byte address architecture. This means that each address contains 1 byte or 8 bits.
Hence, at 0x1004000a0, there is a register that can store 8 bits (or 1 byte) of information.

In other words, at 0x1004000a0, we can contain anywhere from 00000000 to 11111111.

at 0x1004000a1, we can contain another byte of data.

at 0x1004000a2, we can contain another…

Hence from 0x1004000a0 to 0x1004000a3, we have a total of 4, 1 byte registers, that we can store data.

It can store any representations from:
00000000 00000000 00000000 00000000
…
…
11111111 11111111 11111111 11111111

Therefore if we have 4 registers, that means we can store 2^(4 * 8bits) different representations of data.

Since an int can represent 4294967296 different datas, it needs 4 bytes or 32 bits to do it.
That is why an int’s address starts at 0x1004000a0, and ends at 0x1004000a4 – 1.

Chinese Rule of Eight

How to deal with erroneous server db deletion

Delete – server and local

_cmd

How to load profile info

Protected: Download async images into your table

Binary Search Tree part 2

Loose Coupling through Dependency Injection

The Problem

Implementing a protocol and using delegate for loose coupling

But how do we connect them?

Delegates

Protected: Block Storage on Azure using iOS

Adding and Removing Observer in UIView

Protected: from data structure to JSON and back in iOS

Why use hex to represent memory address locations in Programming

example

Converting from Decimal to Hex

Converting from Hex to Decimal

Binary to Hex

From binary to hex

From hex to binary

Easily representing values of bytes

Working with programming languages in IDE