iOS media picker does not show up

I am currently working on an audio application on iPhone. It is based on apple's SpeakHere sample code with a user-defined input file from iPod library.

Here is the event raised by the button:

- (IBAction) btn_PickSong_Clicked:(id)sender{

[self showMediaPicker]; 

//code importing tracks from library
}

And in showMediaPicker method:

//Yup the program does reach this method but the picker does not show up    
- (void)showMediaPicker {

MPMediaPickerController* mediaPicker = [[[MPMediaPickerController alloc] initWithMediaTypes:MPMediaTypeMusic] autorelease];
mediaPicker.delegate = self;
[self presentModalViewController:mediaPicker animated:YES];
}

The problems are:

1. The library import feature works fine in a separate program, but the media picker does not show up anymore when I put the code into SpeakHereController.mm.

2. Also if I place the showMediaPicker method in another class and call it, it does not work either.

Something I find it might be relevant:

1. The original code is in an obj-C file (xxx.m), and now it's transferred into an obj-C++ file (xxx.mm).

2. I have also modified the base class of SpeakHereController.h from NSObject to UIViewController<MPMediaPickerControllerDelegate> otherwise it will throw a warning that the base class does not contain the required delegate. But in the interface builder it is still displayed as an object (Please refer to SpeakHere sample code).

3. It seems that it's i开发者_Go百科llegal to convert the built-in xxxViewController.m file to obj-C++ file (.mm extension). In this case a lot of errors will show up if I attempt to do so. Is it true? If so, how to include C++ code in a pure obj-C file?

=============

So how can I make the media picker show up in this case? Any insight will be appreciated.

Thank you very much!

Cheers,

Manca

In order for

[self presentModalViewController:mediaPicker animated:YES];

to work, self needs to be a viewcontroller. I'm worried that you have just changed the base class to avoid compiler errors as this suggests you are not actually instantiating 'self' correctly.

So how are you initialising the SpeakHereController? As a view controller, this would normally be via the designated initialiser, which for a UIViewController is of course initWithNibName:bundle:

You may find the documentation for UIViewController helpful.

With regards to the C++ issue. Although you can mix objective-c and c++ in the way you suggest, I would recommend that you encapsulate your c++ code in it's own class rather than sprinkling it around your viewcontroller code. That will make it more maintainable for the future.