Core API Guide - Objective-C

Create a New Xcode iOS Project

  1. Open Xcode by selecting it from the Applications folder in the Dock at the bottom of the screen.
  2. Select File > New > Project....
  3. In the left menu, under iOS, select Application and then select Single View Application from the list of possible application types.
  4. Click Next and fill out the name of the new project in the Product Name field, select iPhone as the Device Family, and select the Use Automatic Reference Counting and Use Storyboards options.
  5. Click Next, select the parent folder for your new project, and then select Create. You now should see your HelloAllJoynWorld project loaded in Xcode. You are ready to begin your journey into AllJoyn® development.

Define the AllJoyn Object Model

To offer a service that does some useful work for a client, you must define and implement the service's interface.

For this example, we will create a simple interface with a single method that will concatenate two strings and return the result. The AllJoyn for iOS SDK comes with a utility that will generate most of the boilerplate code for your service objects. All you need to do is provide the Objective-C code to fill in the implementation of each member exposed by the interfaces of your service's bus object.

Before we can run the code generator, though, we need to compose a representation of the service, or bus object, in XML, which is the format the code generator expects. As a side note, the format of the XML conforms to the standard used by D-Bus. The AllJoyn framework implements the D-Bus specification, and hence is compatible with other D-Bus-enabled applications. For more information on D-Bus, you can look up the latest DBus specifications online.

In your HelloAllJoynWorld Xcode project, add a new file called SimpleAllJoynObjectModel.xml that will contain a description of the interface your service will support.

  1. Right-click on the HelloAllJoynWorld group folder in the project Navigator on the right side of the Xcode view.
  2. Select New File... from the menu to bring up the template chooser.
  3. Under iOS, select the Other template group and then select Empty in the list of available templates. Click Next to proceed.
  4. Type in the name of your new file, SampleAllJoynObjectModel.xml.
  5. Click Create to create your new XML file and add it to the Xcode project.
  6. Select the SampleAllJoynObjectModel.xml file in the project Navigator, and add the following XML text:

       <node name="org/alljoyn/Bus/sample">
          <annotation name="org.alljoyn.lang.objc" value="SampleObject"/>
          <interface name="org.alljoyn.bus.sample">
             <annotation name="org.alljoyn.lang.objc" value="SampleObjectDelegate"/>
             <annotation name="org.alljoyn.lang.objc.announced" value="true"/>
             <method name="Concatentate">
                <arg name="str1" type="s" direction="in">
                   <annotation name="org.alljoyn.lang.objc" value="concatenateString:"/>
                <arg name="str2" type="s" direction="in">
                   <annotation name="org.alljoyn.lang.objc" value="withString:"/>
                <arg name="outStr" type="s" direction="out"/>

You now have a description of the bus object that your service will expose to its clients. Let's go line by line through the XML to build an understanding of the format and how it describes our bus object.


The first line, shown above, is standard for all XML documents.

<node name="org/alljoyn/Bus/sample">

The second line declares an element named "node" which corresponds with the bus object our service will expose. A name attribute on the node element defines the object path. In the D-Bus XML format, node elements contain interface elements that can contain method, property and signal elements. Node elements may also contain other child node elements, but let's keep it simple for now.

<annotation name="org.alljoyn.lang.objc" value="SampleObject"/>

The next line declares an annotation element. Annotations are used to store metadata about a node, interface, method, signal or property element. Annotations are name-value pairs that can contain virtually any data. In the context of the AllJoyn framework for iOS, annotations named "org.alljoyn.lang.objc" are used to give the code generator hints as far as naming is concerned. In this instance, the annotation element gives the code generator a hint on what to name the object at path /org/alljoyn/Bus/sample. The annotation tells the code generator to give the object a friendly name of "SampleObject" in any Objective-C code emitted.

<interface name="org.alljoyn.bus.sample">
<annotation name="org.alljoyn.lang.objc" value="SampleObjectDelegate"/>
<annotation name="org.alljoyn.lang.objc.announced" value="true"/>

On the above lines, an interface element named org.alljoyn.bus.sample is created. Interface elements contain method, signal and property elements, as well as annotation elements.

The first annotation tells the code generator to create an Objective-C protocol for the interface and name it SampleObjectDelegate. All interfaces on bus objects are implemented in Objective-C as protocols.

The second annotation tells the code generator that the objects implementing this interface must be announced through the About discovery mechanism. The code generator will generate the necessary code to make this happen.

<method name="Concatentate">
    <arg name="str1" type="s" direction="in">
        <annotation name="org.alljoyn.lang.objc" value="concatenateString:"/>
    <arg name="str2" type="s" direction="in">
        <annotation name="org.alljoyn.lang.objc" value="withString:"/>
    <arg name="outStr" type="s" direction="out"/>

The final lines in the XML file shown above describe a method named Concatenate that takes two strings as arguments and returns one string. A method element can contain 0 to n arg child elements. Each arg element has three attributes:

  • Name - The name of the argument.
  • Type - The type of the element. Per the D-Bus specification, data types are expressed as a string of one or more letters, called a signature. The letter "s" signifies a string data type.
  • Direction - Allowed values are "in" or "out", corresponding to input and output parameters respectively.

The D-Bus interface description format favors a C language style for declaring methods, with a name for a method followed by several input and output parameters, each with a parameter name. Objective-C, however, does not use this syntax when declaring a method, or more accurately in Objective-C parlance, a message. The message takes the form of a selector, with the complete name of the message interspersed with its parameters. Note the difference below:

void ConcatenateString(in String str1, in String str2, out String outStr);

NSString *concatenateString:(NSString *)str1 withString:(NSString *)str2;

Annotations help the code generator create message declarations that appeal to our Objective-C sense of good coding style. The arg elements contain an annotation element that specifies part of the selector associated with that argument. By processing all the arg elements and their child annotations, the code generator can emit the complete selector for the message.

Build and Configure the Code Generator

Now that you have familiarized yourself with the D-Bus XML format, it is time to generate the code that will allow us to create an Objective-C object that you can use in your application. The AllJoynCodeGenerator project is located at the following path:

<AllJoyn SDK Root>/alljoyn_objc/AllJoynCodeGenerator

Navigate to the above directory in Finder and double-click the AllJoynCodeGenerator.xcodeproj file to launch Xcode and load the project. In Xcode, select Product > Build to build the AllJoyn code generator executable. Your new executable is now ready for use, and is located in the following directory:

<AllJoyn SDK Root>/alljoyn_objc/bin

Now return to your HelloAllJoynWorld Xcode project, so that you may configure a target and a scheme in Xcode that will launch the code generator and pass the SampleAllJoynObjectModel.xml file to it.

  1. Select the HelloAllJoynWorld root node in the Project Navigator view, displayed in the left pane in Xcode, and then click Add Target located at the bottom of the middle pane.
  2. Select Other in the OS X list on the left side of the dialog and choose the External Build System type for your new target. Click Next.
  3. Type Generate Code into the Product Name field and click Finish to create your new target and its accompanying scheme.
  4. Select the Generate Code target in the list of targets, and select the Info tab at the top of the middle pane in Xcode.
  5. In the Build Tool text field for the "Generate Code" target, enter the full path to your AllJoynCodeGenerator binary, which should be located in your <ALLJOYN_SDK_ROOT>/alljoyn_objc/bin folder.
  6. In the Arguments text field for the "Generate Code" target, enter the full path to your SampleAllJoynObjectModel.xml file followed by a space and then SampleObject, as follows:

    $(SOURCE_ROOT)/HelloAllJoynWorld/SampleAllJoynObjectModel.xml SampleObject
  7. Select the Generate Code scheme and set it to your active scheme.
  8. Click Product > Build and the code generator should successfully generate your SampleObject code. Add the new files to your project by right-clicking on the HelloAllJoynWorld group and selecting Add Files To HelloAllJoynWorld.
  9. Select the following files and click Add:


Congratulations! You now have a skeleton Objective-C implementation of your sample AllJoyn bus object.

Take a look at the generated code files. As you can see, the code generator takes care of the implementation of most of the boilerplate you would normally need to create by hand to work with the AllJoyn C++ API. Also note that the code in includes C++ code that interoperates with the Objective-C code contained in SampleObject.h/.m. By declaring and implementing the C++ classes only within the file and not referring to any C++ classes in the header file, the code generator insulates your app's code from the AllJoyn C++ API. In this manner, the rest of your app can remain as pure Objective-C, rather than forcing you to move your entire project's code to Objective-C++.

Your implementation of the logic for SampleObject::concatenateString:withString: should reside in the SampleObject.m. You normally should not need to change the code in the AJN*.h/.mm files in order to implement your application.

Configure the Build Settings

Now you must configure the Xcode project to successfully compile and link your app.

  1. Make sure you know the location of the AllJoyn SDK folder. The AllJoyn SDK folder contains your build, services, and alljoyn_objc folders.
  2. Follow the directions in the README file in the AllJoyn SDK folder to compile openssl for iOS using Xcode.
  3. Open Xcode, open your project, and select the root of the tree in Project Navigator. Then select the app's target under Targets.
  4. Select the Build Settings tab for the app target. Click the All option at the top of the list.
  5. At the top of the Build Settings list, click Architectures and then select Other....
  6. Click the + sign in the window that appears and add armv7, then close the window.
  7. Set Build Active Architecture Only to Yes.
  8. Scroll down to the Linking section, and set Other Linker Flags to the following:
    -lalljoyn -lajrouter -lBundledRouter.o -lssl -lcrypto
  9. Scroll down the list of settings until you see the Search Paths group.
  10. Double-click the Header Search Paths field and enter the following:
    "$(SRCROOT)/../alljoyn- sdk/
    build/darwin/arm/$(PLATFORM_NAME)/$(CONFIGURATION)/dist/ cpp/inc"
    "$(SRCROOT)/../alljoyn- sdk/
    build/darwin/arm/$(PLATFORM_NAME)/$(CONFIGURATION)/dist/ cpp/inc/alljoyn"
  11. Double-click the Library Search Paths field and enter the following:
    $(inherited) "$(SRCROOT)/../alljoyn- sdk/
    build/darwin/arm/$(PLATFORM_NAME)/$(CONFIGURATION)/dist/ cpp/lib"
  12. Scroll down in the Build Settings table until you see the Apple LLVM compiler 3.1 - Language group.
  13. Set Enable C++ Exceptions to No.
  14. Set Enable C++ Runtime Types to No.
  15. Set the Other C Flags field for Debug to the following:
  16. Set the Other C Flags field for Release to the following:
  17. Select the Build Phases tab.
  18. Expand the Link Binary With Libraries group and click the + sign at the lower left corner. A dialog will appear.
  19. Select the SystemConfiguration.framework file.
  20. Click the + button again and add one last library to link against, if it is not already included: libstdc++.dylib.
  21. Enter "std" into the search text field to view only the standard template library binaries. Select the following file from the list: libstdc++.dylib.
  22. Create a group to hold the AllJoyn framework by right-clicking the HelloAllJoynWorld group in the Project Navigator tree and selecting New Group from the menu.
  23. Enter "AllJoynFramework" to give your new group a pertinent name.
  24. Select the newly-created group "AllJoynFramework", and choose Add Files....
  25. Navigate to the following folder:
  26. Select all the .h/.m* files in the directory, and be sure to uncheck Copy items into destination group's folder, and make sure your HelloAllJoynWorld target is checked in the Add to targets list.
  27. Click Add to add the AllJoyn Objective-c framework to your AllJoynFramework group in the project.
  28. Select Product > Build from the Xcode main menu. Your project should build successfully. Congratulations.

Note that there is a template project located in the following folder that has the above configuration preloaded for you. Check it out at:

<ALLJOYN_SDK_ROOT>/alljoyn_objc/samples/iOS/AllJoyn iOS Project Template

This is a good starting point for any applications you may wish to build. Open the Xcode project for the above template and examine the source files within. Allow some time to examine the README file included with this project, as it contains information on the files included in the project.