passing data between views

Question

So i'm trying to pass data between two views (first view is tableViewController,when cell is pressed data is send to second view,second view got imageView, when data is send image is shown) using this tutorial iphonedevsdk.

I'm using same theAppDataObject method in my views:

- (AppDataObject*) theAppDataObject
{
    id<AppDelegateProtocol> theDelegate = (id<AppDelegateProtocol>) [UIApplication sharedApplication].delegate;
    AppDataObject* theDataObject;
    theDataObject = (AppDataObject*) theDelegate.theAppDataObject;
    return theDataObject;
}

When cell is pressed i'm trying to send data theAppDataObject.imageString = tempImageString;:

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    tempImageString = (((championList *) [self.champions objectAtIndex:indexPath.row]).championImage);

    AppDataObject *theDataObject = [self theAppDataObject];
    NSLog(@"tempIm-g = %@",tempImageString);
    theDataObject.imageString = tempImageString;
    NSLog(@"theAppDataObject.imageString = %@",theDataObject.imageString);

    [self.navigationController popToRootViewControllerAnimated:YES];
}

NSLog output:

tempIm-g = Champ_0.jpg

theAppDataObject.imageString = (null)

SecondViewController (show image):

-(void)viewWillAppear:(BOOL)animated
{
    AppDataObject* theDataObject = [self theAppDataObject];
    UIImage *tempImage = [UIImage imageNamed:theDataObject.imageString];
    NSLog(@"temp image = %@",tempImage);
    [choosenChampionImageView setImage:tempImage];
}

NSLog output:

temp image = (null)

My problem is that theAppDataObject.imageString is always null

---

Possible solutions that i know:

Do not use AppDataObject as generic data container and just save data in appDelegate.

Ex.:

AppDelegate *appdelegate = (AppDelegate *)[[UIApplication sharedApplication]delegate];
appdelegate.imageString = tempImageString;

But i want to figure out how to use protocols.

What i tried: Make theDataObject global:

view1.h

@interface championsListTableViewController : UITableViewController
{
    NSString *tempImageString;

    AppDataObject* theDataObject;
}

@property(strong,nonatomic) NSString *tempImageString;

@property(strong,nonatomic) AppDataObject* theDataObject;

output of NSLog(@"theDataObject is %@",theDataObject); :

theDataObject is (null), how is this possible?

Answer 1

In a class if you want to use a protocal you can use like as :

  // this the way too declare  a protocal.
  // .h file
 @protocol TestProtocol <NSObject>

 -(void)testMyProtocolMethod:(NSString *)testvalue;

 @end

@interface TestProtocolClass: NSObject
{
   id <TestProtocol> delegate;

}
 @property (nonatomic , assign) id <TestProtocol> delegate;
 /* synthesize in the .m file   of          this      class*/
 @end



 //Now you have to use this protocol in any class where you want to use , Do like as:
 //let us suppose you want to use this protocal method in a class named "DemoProtocal".
 // .h file 
 import "TestProtocol.h"
 @interface DemoProtocal <TestProtocol>{

 }
 @end

//.m file
 #import "DemoProtocal.h"
 @implementation DemoProtocal

- (id)init{

  TestProtocol *test = [[TestProtocol alloc]init];
  test.delegate = self;

 }

-(void)testMyProtocolMethod:(NSString *)testvalue{

  // Do appropriate things.
 }
 @end

Answer 2

First Check theAppDataObject is null or not.

If it is null then:

Write AppDataObject* theDataObject; in your inteface and declare a property as strong

If theDelegate.theAppDataObject is returning null , allocate that object first.

If it is not null then:

Change this line theAppDataObject.imageString = tempImageString;

to

theAppDataObject.imageString = [tempImageString retain];

If you are using ARC set the property of imageString to strong.

or Check with this

theAppDataObject.imageString = [[NSString alloc] initWthString:tempImageString];

Answer 3

In any class where you want to set any variable of the "AppDelegate Class", you can try this, this will surely solve your problem.

 //Declare a variable from where you want to set the value of the "AppDelegate Class". 
 //in the yourclass.h file.
 AppDelegate/* this is the main class of the Application*/ *appDel;

//and initialize it where you want to use or you can initialize at the init of the class.  

appDel = (AppDelegate *)[[UIApplication sharedApplication]delegate];

 // Then set the value.
 appDel.imageString = tempImageString;