How to initialize an object and override a method in objective c? - objective-c

Question

Like Other Language, We can create a object and override a method in the object during initialization. Please help me How can i do?
For Example:
public class DemoInitAndOverride {
public void handleMessage(){}
}
And in another class
public class SampleClass {
public void doSomeThing(){
DemoInitAndOverride demo = new DemoInitAndOverride(){
#Override
public void handleMessage() {
// TODO Auto-generated method stub
super.handleMessage();
}
};
}
}
****EDIT:****
Thanks everyone for possible solutions and suggestion. I think now it is important for me provide some details about the requirement which could help you in providing the solution.
The handler concept is some thing similar to the Android Framework where handlers are used to pass messages between 2 threads or 2 methods. Please see the code demonstration below:
UI Class (Here the user clicks a button, a request is dispatched to the processor class using handler)
This is the demo handler
/**
*
* Used for thread to thread communication.
* Used for non UI to UI Thread communication.
*
*/
public class DemoHandler {
public void handleMessage(Messages message){}
final public void sendMessage(final Messages message){
//Calling thread is platform dependent and shall change based on the platform
new Thread(new Runnable() {
#Override
public void run() {
synchronized (this) {
handleMessage(message);
}
}
});
}
}
This is simple message class
public class Messages {
public Object myObject;
//other hash map (key, values) and get data put data etc
}
This is simple user interface class demo code:
public class UIClass {
public UIClass(){
//INIT
}
void onClick(int id){
//Some Button is clicked:
//if id == sendParcel
//do
TransactionProcessor.getInstance().sendParcel(handler, "Objects");
}
DemoHandler handler = new DemoHandler(){
public void handleMessage(Messages message) {
//Inform the UI and Perform UI changes
//data is present in the messages
};
};
}
This is sample transaction processor class
public class TransactionProcessor {
public static TransactionProcessor getInstance(){
return new TransactionProcessor(); //for demonstration
}
//Various Transaction Methods which requires calling server using HTTP and process there responses:
public void sendParcel(final DemoHandler uiHander, String otherdetailsForParcel){
//INIT Code and logical code
//Logical Variables and URL generation
String computedURL = "abc.com/?blah";
DemoHandler serverConnectionHandler = new DemoHandler(){
#Override
public void handleMessage(Messages message) {
super.handleMessage(message);
//Process server response:
//create a new message for the UI thread and dispatch
Messages response = new Messages();
//add details to messages
//dispatch
uiHander.sendMessage(response );
}
};
new Thread(new ServerConnection(computedURL, serverConnectionHandler));
}
public void sendEmail(final DemoHandler uiHander, String otherdetailsForEmail){
//SAME AS SEND PARCEL WITH DIFFERENT URL CREATION AND RESPONSE VALIDATIONS
}
public void sendNotification(final DemoHandler uiHander, String otherdetailsForNotifications){
//SAME AS SEND PARCEL WITH DIFFERENT URL CREATION AND RESPONSE VALIDATIONS
}
}

Answer 1

This is a nasty one, and I recommend creating a subclass or something else.
Here's your answer, which is essentially the same, but at runtime. Proceed at your own risk:
Import this:
#import <objc/runtime.h>
And add this code to wherever:
- (void)methodName {
// whatever you want to do in there
}
And in your function:
Class subclass;
// Verifiy that you haven't created it already
subclass = objc_getClass("SampleClassSubclass");
if (!subclass) {
// Generate a new class, which will be subclass of your SampleClass
subclass = objc_allocateClassPair(subclass, "SampleClassSubclass", 0);
// Obtain the implementation of the method you want to overwrite
IMP methodImplementation = [self methodForSelector:#selector(methodName)];
// With that implementation, replace the method
class_replaceMethod(subclass, #selector(methodName), methodImplementation, "##:");
// Register the class you just generated
objc_registerClassPair(subclass);
}
SampleClass *obj = [[subclass alloc] init];

Answer 2

Not so easy to do in Objective-C, but this should work. It replaces the doSomething method of DemoInitAndOverride with its own implementation and returns a new instance of the class. Note however that once this has been done the new implementation remains in place for all new instances of the class, not just a single instance.
- (void)doSomething
{
NSLog(#"self doSomething called");
}
- (DemoInitAndOverride *)createObj
{
DemoInitAndOverride *obj = [[DemoInitAndOverride alloc] init];
SEL sel = #selector(doSomething);
Method theirMethod = class_getInstanceMethod([DemoInitAndOverride class], sel);
Method myMethod = class_getInstanceMethod([self class], sel);
theirMethod->method_imp = myMethod->method_imp;
return obj;
}