С in лун programming

С in лун programming

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Key-Value Coding Programming Guide

About Key-Value Coding

Key-value coding is a mechanism enabled by the NSKeyValueCoding informal protocol that objects adopt to provide indirect access to their properties. When an object is key-value coding compliant, its properties are addressable via string parameters through a concise, uniform messaging interface. This indirect access mechanism supplements the direct access afforded by instance variables and their associated accessor methods.

You typically use accessor methods to gain access to an object’s properties. A get accessor (or getter) returns the value of a property. A set accessor (or setter) sets the value of a property. In Objective-C, you can also directly access a property’s underlying instance variable. Accessing an object property in any of these ways is straightforward, but requires calling on a property-specific method or variable name. As the list of properties grows or changes, so also must the code which accesses these properties. In contrast, a key-value coding compliant object provides a simple messaging interface that is consistent across all of its properties.

Key-value coding is a fundamental concept that underlies many other Cocoa technologies, such as key-value observing, Cocoa bindings, Core Data, and AppleScript-ability. Key-value coding can also help to simplify your code in some cases.

Using Key-Value Coding Compliant Objects

Objects typically adopt key-value coding when they inherit from NSObject (directly or indirectly), which both adopts the NSKeyValueCoding protocol and provides a default implementation for the essential methods. Such an object enables other objects, through a compact messaging interface, to do the following:

Access object properties. The protocol specifies methods, such as the generic getter valueForKey: and the generic setter setValue:forKey: , for accessing object properties by their name, or key, parameterized as a string. The default implementation of these and related methods use the key to locate and interact with the underlying data, as described in Accessing Object Properties .

Manipulate collection properties. The default implementations of the access methods work with an object’s collection properties (such as NSArray objects) just like any other property. In addition, if an object defines collection accessor methods for a property, it enables key-value access to the contents of the collection. This is often more efficient than direct access and allows you to work with custom collection objects through a standardized interface, as described in Accessing Collection Properties .

Invoke collection operators on collection objects. When accessing a collection property in a key-value coding compliant object, you can insert a collection operator into the key string, as described in Using Collection Operators . Collection operators instruct the default NSKeyValueCoding getter implementation to take an action on the collection, and then return either a new, filtered version of the collection, or a single value representing some characteristic of the collection.

Access non-object properties. The default implementation of the protocol detects non-object properties, including both scalars and structures, and automatically wraps and unwraps them as objects for use on the protocol interface, as described in Representing Non-Object Values . In addition, the protocol declares a method allowing a compliant object to provide a suitable action for the case when a nil value is set on a non-object property through the key-value coding interface.

Access properties by key path. When you have a hierarchy of key-value coding compliant objects, you can use key path based method calls to drill down, getting or setting a value deep within the hierarchy using a single call.

Adopting Key-Value Coding for an Object

In order to make your own objects key-value coding compliant, you ensure that they adopt the NSKeyValueCoding informal protocol and implement the corresponding methods, such as valueForKey: as a generic getter and setValue:forKey: as a generic setter. Fortunately, as described above, NSObject adopts this protocol and provides default implementations for these and other essential methods. Therefore, if you derive your objects from NSObject (or any of its many subclasses), much of the work is already done for you.

In order for the default methods to do their work, you ensure your object’s accessor methods and instance variables adhere to certain well-defined patterns. This allows the default implementation to find your object’s properties in response to key-value coded messages. You then optionally extend and customize key-value coding by providing methods for validation and for handling certain special cases.

Key-Value Coding with Swift

Swift objects that inherit from NSObject or one of its subclasses are key-value coding compliant for their properties by default. Whereas in Objective-C, a property’s accessors and instance variables must follow certain patterns, a standard property declaration in Swift automatically guarantees this. On the other hand, many of the protocol’s features are either not relevant or are better handled using native Swift constructs or techniques that do not exist in Objective-C. For example, because all Swift properties are objects, you never exercise the default implementation’s special handling of non-object properties.

Therefore, while the key-value coding protocol methods translate straightforwardly to Swift, this guide focuses primarily on Objective-C, where you need to do more to ensure compliance, and where key-value coding is often most useful. Situations that call for a significantly different approach in Swift are noted throughout the guide.

For more information about using Swift with Cocoa technologies, read Using Swift with Cocoa and Objective-C (Swift 3) . For a complete description of Swift, read The Swift Programming Language (Swift 3) .

Other Cocoa Technologies Rely on Key-Value Coding

An object that is key-value coding compliant can participate in a wide range of Cocoa technologies that depend upon this kind of access, including:

Key-value observing. This mechanism enables objects to register for asynchronous notifications driven by changes in another object’s properties, as described in Key-Value Observing Programming Guide.

Cocoa bindings. This collection of technologies fully implement a Model-View-Controller paradigm, where models encapsulate application data, views display and edit that data, and controllers mediate between the two. Read Cocoa Bindings Programming Topics to learn more about Cocoa Bindings.

Core Data. This framework provides generalized and automated solutions to common tasks associated with object life cycle and object graph management, including persistence. You can read about Core Data in Core Data Programming Guide.

AppleScript. This scripting language enables direct control of scriptable apps and of many parts of macOS. Cocoa’s scripting support takes advantage of key-value coding to get and set information in scriptable objects. The methods in the NSScriptKeyValueCoding informal protocol provide additional capabilities for working with key-value coding, including getting and setting key values by index in multi-value keys and coercing (or converting) a key-value to the appropriate data type. AppleScript Overview provides a high-level overview of AppleScript and its related technologies.

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Securing API Keys in Android App using NDK (Native Development Kit)

Securing API keys in Android application has become a challenging by traditional methods (storing them in strings.xml or in Gradle etc.), since they can be easily exposed by reverse engineering the app. It may lead to privacy issues and also may affect the billing for third party paid API access.

Though its not possible to fully protect this API keys from reverse engineering but we can make extra laye r for security by using NDK in our app.

The NDK (Native Development Kit) allows to write code in C/C++ in our app. And the good news is that ndk libraries can not be decompiled easily which make the APIs harder to find.

Today, We are going to store API keys in the native C/C++ class and accessing them in our Java classes. Now Let’s started:

Requirements

To compile and debug native code for our app, we need the following components:

The Android Native Development Kit (NDK):

a set of tools that allows to use C and C++ code with Android.

CMake:

an external build tool that works alongside Gradle to build your native library. You do not need this component if you only plan to use ndk-build.

the debugger Android Studio uses to debug native code.

You can install these components using the SDK Manager:

• From an open project, select Tools > Android > SDK Manager from the menu bar.
• Click the SDK Tools tab.
• Check the boxes next to LLDB, CMake, and NDK, as shown in below figure:

Two ways for using NDK: ndk-build, CMake

• NDK is a collection of compilers and libraries that are needed to build C/C++ code for android.
• ndk-build and CMake both use the NDK and solve the same problem.

— — CMake:

• CMake is a new way and the default build tool for using ndk. If we are creating new native library , then we should use CMake.

— — ndk-build:

• Android studio also support this ndk-build(this is a build system included in NDK) due to the large number of existing projects that use the build toolkit to compile their native code.
• It uses android.mk files. in other way we can say android.mk file contains ndk-build.
• If you use CMake then you don’t need Android.mk instead you will need CMakeList.txt

CMake or ndk-build .

• If you’re not familiar with either or your project is cross platform, CMake is probably the better choice. Because CMake’s main advantage is that you can use one set of build files for all your targets (Android, Linux, Windows, iOS, etc).
• ndk-build should be preferred if you’re building a project that already uses Android.mk files for its build system (legacy projects).

***Securing Keys using ndk-build…(Item-01)

step 01: Create a folder “jni” under src/main.

step 02: Create a file ‘Android.mk’ under “jni” folder with following content:

step 03: Create another file ‘Application.mk’ file under “jni” folder with the following content:

Here, This is for setting different Application Binary Interface or ABI. More details can be found at Application.mk.

step 04: Create the C/C++ file “keys.c” under “jni” folder. Add the following content to it:

• “Java_com_shishirstudio_ndktest_MainActivity_getFacebookApiKey”: represents the Java code with package name “com.shishirstudio.ndktest” [ dot(.) must be replaced with underscore(_)]followed by Activity name “MainActivity” where we want to call the native function and the static method “getFacebookApiKey” to fetch the API key from the native function. So the combination is:< Package Name>__
• In the above code, I have encoded the actual API key using Base64 encoding (You can store actual API key) for making another security layer.

step 05: Add a static block and load the library ‘keys’ in the activity where you will access the keys. (In our case in MainActivity).

step 06: We also have to add member functions of type “native” to access the keys from the C/C++ file. Since we stored 2 keys, we will declare 2 functions:

step 07: Now access the keys in the code like:

step 08: Oh ! one more things, to compile or make the native build using NDK, don’t forget to add entry into the gradle file:

step 09: Now, sync and build the project. And you will find everything is ok….

***Securing Keys using CMake…(item-02)

step 01: Create a new project or use existing project.

step 02: Create a folder named “cpp” under src/main.

step 03: Create the C/C++ file “native-lib.cpp” under “cpp” folder. And add the following content to it:

• “Java_com_shishirstudio_ndktest_MainActivity_stringFromJNI”: represents the Java code with package name “com.shishirstudio.ndktest” [ dot(.) must be replaced with underscore(_)]followed by Activity name “MainActivity” where we want to call the native function and the static method “stringFromJNI” to fetch the API key from the native function. So the combination is:< Package Name>__

Now the directory looks like below…

step 04: Create a CMake build script CMakeLists.txt under app folder ( This is a plain text file that you must name CMakeLists.txt ) and add the following content to it.

Step 05: Now, our C/C++ native files and Java code are ready. But to compile or make the native build using NDK, we need to add entry into the gradle file:

Step 06: To use this API follow the step 05,06 and 07 of item-01.

***** The easiest and best way*****

In the newer updates of Android Studio its very easy because everything will be ready for you automatically. Just follow the below step:-

step 01: Enable “include C++ support” while taking a new project in android studio.

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