Objective-C-复制exit（0）并修复EXC_BAD_ACCESS

Question

Having some seriously frustrating issues with my latest app!!

I'm using OpenGLES 1 to draw models to the screen that are constantly updating, then you can take a screenshot and share however you like, after that you can return to the app start screen and start again.

All seems to work fine the first time the app runs through, no crashes. But if you run through it once then try to go through again, as soon as the OpenGLES drawing view has to start drawing the elements, it throws up an EXC_BAD_ACCESS error on my glDrawElements line.

I given up on trying to fix this error for now, I've had no luck in the last 2 weeks!!

I have set the property in my plist so that the app doesn't run in the background, and whenever I run it through once, then exit it and load it up again it will run through again absolutely fine.

So what I was wondering is if I could somehow emulate the functionality of the exit(0) feature, but without actually exiting from the app?

So in essence, each time the user navigates from the sharing page back to the home page, the app would run the exit code, leaving the app to run from scratch again.

This would, in my head at least, not be a great way at all of dealing with the situation, but I need results quick and this seems like a good way out for now until I can get to the bottom of the actual error.

Thanks,

Matt

EDIT 1: I'm not looking to put the app on the store with this fix in place, it is just a temporary thing.

EDIT 2: Posted code containing my draw functionality, taken and adapted from Bill Dudney's WaveFront .obj loader

for(WaveFrontOBJGroup *group in scene.groups)
{
    NSString *matPath = [NSString stringWithFormat:@"%@%@.mtl", materialName, modelPart];
    NSArray *materialArray = [WaveFrontOBJMaterial materialsFromLibraryFile:matPath];
    WaveFrontOBJMaterial *mat = [materialArray objectAtIndex:0];

    if(group.smoothing)
        glShadeModel(GL_SMOOTH);
    else
        glShadeModel(GL_FLAT);

    // load (if necessary) and bind the vertices
    GLuint verticesName = [group verticesName:GL_STATIC_DRAW];
    glBindBuffer(GL_ARRAY_BUFFER, verticesName);
    glVertexPointer(3, GL_FLOAT, 0, 0);

    // load (if necessary) and bind the normals
    GLuint normalsName = [group normalsName:GL_STATIC_DRAW];
    glBindBuffer(GL_ARRAY_BUFFER, normalsName);
    glNormalPointer(GL_FLOAT, 0, 0);

    ColorRGBA color = mat.ambientColor;
    glMaterialfv(GL_FRONT_AND_BACK, GL_AMBIENT, (GLfloat *)&color);
    color = mat.diffuseColor;
    if(alpha)
        glColor4f(color.red, color.green, color.blue, mat.disolve);
    else
        glColor4f(color.red, color.green, color.blue, color.alpha);
    glMaterialfv(GL_FRONT_AND_BACK, GL_DIFFUSE, (GLfloat *)&color);
    color = mat.specularColor;
    glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, (GLfloat *)&color);
    glMaterialf(GL_FRONT_AND_BACK, GL_SHININESS, mat.shine);

    // load (if necessary) and bind the texture
    if(group.textureCoordinatesIndexData.length > 0)
    {
        glEnableClientState(GL_TEXTURE_COORD_ARRAY);
        GLuint textureCoordsName = [group textureCoordinatesName:GL_STATIC_DRAW];
        glEnable(GL_TEXTURE_2D);
        glBindBuffer(GL_ARRAY_BUFFER, textureCoordsName);
        glTexCoordPointer([group texCoordSize], GL_FLOAT, 0, 0);
        GLuint texId = [mat.diffuseTexture textureName];
        glBindTexture(GL_TEXTURE_2D, texId);
    }

    GLuint indexesName = [group indexesName:GL_STATIC_DRAW];
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexesName);

    glDrawElements(GL_TRIANGLES, group.indexCount, GL_UNSIGNED_SHORT, NULL);
    //^^This line above is where I get the "EXC_BAD_ACCESS" message

    if(group.textureCoordinatesIndexData.length > 0)
        glDisableClientState(GL_TEXTURE_COORD_ARRAY);
}

I've checked group.indexCount through breakpoints and NSLog's and it is not null, it is exactly the same as when it runs through the first time which works fine.

I realise it won't necessarily be on that line, I've heard other talk about it being due to variables not being initialised as pointers - * - or NSStrings not having matching identifiers and values (@"%@ sometext %@", variable); but I don't see any of those in my code, of course I could easily be missing one.

Answer 1

Remember two things:

1) You have a method -(void)viewWillAppear:(BOOL)animated in your home ViewController. This will call always (!) when user return to this screen (not like viewDidLoad).

2) If you even do this like you described you probably didn't get to the AppStore!

Answer 2

I'm not sure why your application won't compile on the simulator, but you should try to link your libraries appropriately so that you can get that up and running - nothing is better for bad access errors than zombies.

If you know your error is from calling glDrawElements then you should look into what's being passed to it. This link might be able to help you.

The reason you can't get the "functionality" of exiting your app while still in the app is because it's not a function of the application - it's the OS throwing away everything associated with the application and then reloading it. By definition you won't be able to do this without actually shutting down.

However, if your problem is fixed by this, then it is likely that there's something in your setup that needs to be redone (initializations, declarations, etc). Check to see what's getting set to nil or thrown away and then set it back up.

Without looking at your code I can't say this with any certainty, but you may be able to write a method that overwrites/reinitializes all of your current variables. This would probably replicate the part of exiting the application that you need.