AndroidManifest.xml

• Leaving, res and returning to our project main folder... If we double-click on the AndroidManifest.xml we see we can edit various properties of our project.
  
• Beneath the form we see a row of tabs.
• Under the the Application tab we can fill in the icon we are using for the project.
• The AndroidManifest.xml tab let's us see the raw XML of this file.

Running App

• We can run our trivial application in the emulator by right clicking on our project in Eclipse, and selecting Run As - Android Application.
• This will launch the emulator and we'll see:

The Basics of an Objective-C Program

• For our second iPhone program we are going to actually write code rather than just use Interface Builder.
• This code will be in Objective-C so we are going to go over the Basics of Objective-C.
• Objective-C can be compiled from the command-line in any environment in which you have gcc. We will first look at such a program then work our way back to the iPhone.
• Header Files use the extension .h
• Implementations use the extension .m (named for mplementation)
• A .h file typically might be used to define an interface of a class. This might have the format:

  
  @interface classname : superclassname {
     int my_field; 
      // instance variables can be any C type or  the generic id type.
  }
  +classMethod1; // + means class method; - means instance method
  +(return_type)classMethod2;
  +(return_type)classMethod3:(param1_type)parameter_varName;
  -(return_type)instanceMethod1:(param1_type)param1_varName :(param2_type)param2_varName;
  -(return_type)instanceMethod2WithParameter: (param1_type)param1_varName andOtherParameter:(param2_type)param2_varName;
  @end
  

Implementation Files

To implement the functions you use an implementation file and the syntax:

@implementation classname
+classMethod {
    // implementation
}
-instanceMethod {
    // implementation
}
@end

Invoking Methods

• A call obj.method(parameter); in C++ might look like [obj method:parameter]; in Objective-C.
• You can have multiple parameters:

  [obj method:parameter1 paramName2: parameter2]
  

• To instantiate a class you can send either the new message or instantiate in two steps:

      MyObject * o = [MyObject new];
      MyObject * o = [[MyObject alloc] init];
  

  You can override the init method of your class to make a new constructor.
• The second way is preferred. We first allocate memory for our object; then send it an init message.
• Rather than just init we might create a method that takes arguments and inits, in which case the second approach is more flexible.

Example Objective-C Program

// Interface File
#import <objc/Object.h>

@interface MyHello: Object {
   int myNumber;
   int myOtherNumber;
}
-(void)setNumber:(int) aNumber other:(int) bNumber;
-(void)sayHello;
@end

Example Program cont'd

// implementation file
#import <stdio.h>
#import "MyHello.h" 
@implementation MyHello
-(void)setNumber:(int)aNumber other:(int)bNumber {
    myNumber = aNumber;
    myOtherNumber = bNumber;
} 
-(void) sayHello {
   printf("Hello! %d\n", myNumber + myOtherNumber);
} 
-(id) init { //self is like this in Java
    self = (id)[super init];
    if (self) { 
        myNumber = 0;
        myOtherNumber = 0; 
    }
    return self;
}
@end

Objective-C Example Last Part.

#import "MyHello.h"
int main(void) {
   MyHello *hello = [[MyHello alloc] init];
   //set the number to echo
   [hello setNumber:10 other:5];
   [hello sayHello];
   return 0;
}

/* To compile in gcc could type:
gcc -arch i386 -x objective-c -Wno-import main.m MyHello.m -lobjc  

To get this to work on 64 bit architecture/llvm you need to switch to NSObject (
have at least GNUStep available on non-Macs)...
You can actually build XCode projects from the command line:
/Developer/usr/bin/xcodebuild -target project
*/

The point of the above is to see the basics of Objective-C without reference to iOS or OSX, next week we'll go back to looking at the language in the specific context of Apple.