Robert C. Martin: Clean Architecture and Design

You can declares iVar-s in header files but it’s better in the implementation, so they will be really invisible for others.
You should do this way:

@implementation MyClass {
    int firstiVar;
}
@synthesize anyProperty;

But what if you forget the parenthesis and you put the variable simply beside the @synthesize?
Like this:

@implementation MyClass

int firstiVar;

@synthesize anyProperty;

The compiler will treat it like other variables outside the class. So they will be global variables. Unfortunately in this case these variables is not just shared among all instances but shared in the whole project. What does it mean? It means if you set the value in one instance to 1, and later you set it to 2 in another instance, the value will be 2 for both (since you only have one instance in fact instead of two). AND since it wasn’t marked as static if you have an other global variable with the same name that will be shared together with the variables in the class, even if you did it accidentally.

WARNING: you won’t get any warning or error. It could be a pain in your ass to find these kind of bugs.

So just to clarify:

int firstVar; // global variable, shared and accessible in the whole project and all instances
static int firstStaticVar; // global variable shared among all instances, accessible from only this file

@implementation MyClass {
    int firstiVar;
static firstStaticIVar;// compile error, cannot do this
}

int secondiVar; // !!! the same as firstVar !!!
static secondStaticIVar; // the same as firstStaticVar

@synthesize anyProperty;

Good luck!

 

There is a fancy solution to present the scrolling position of a tableview to the user using moving image as a background. The user can better imagine the size of the table view because the background image suggest where he/she is in the tableview.

How-To – short version

1. Add a tableview
2. create a scrollview with an imageview which size and contentSize is the same as the tableview
3. add the scrollview as a background view of the tableview
4. set the tableview to transparent
5. Good To Know: the TableView is a ScrollView so you can handle all ScrollViewDelegate related methods. Just simply implement the ScrollView delegate methods where you implemented the TableViewDelegate methods: catch the tableview’s scrolling event and position the scroll position of the background scrollview accordingly

How-To – detailed version

First, in the ViewDidLoad of your ViewController load the appropriate image, create an image view which presents it  and add the ImageView as the subview of your ScrollView:

- (UIView *)createBackgroundScrollViewWithFrame:(CGRect)tableViewFrame {

    // set up the image view, select a long image
    UIImage *img = [UIImage imageNamed:kImageName];

    // create image view with the image, the size should be long enough for the scroll
    UIImageView *imgView = [[UIImageView alloc] initWithImage:img];
    imgView.contentMode = UIViewContentModeScaleToFill;
    imgView.frame = CGRectMake(0,0, tableViewFrame.size.width, img.size.height);

    // set up the background scroll view and add the image view
    UIScrollView *backgroundScrollView = [[UIScrollView alloc] initWithFrame:tableViewFrame];
    backgroundScrollView.userInteractionEnabled = NO;
    backgroundScrollView.contentSize = imgView.frame.size;
    [backgroundScrollView addSubview:imgView];

    return backgroundScrollView;
}

 

Second, set the ScrollView as the backgroundView of your tableView:

    // set the scroll view as the background view of the tableview
    myTableView.backgroundView = [self createBackgroundScrollViewWithFrame:theTableView.bounds];

Third, don’t forget to set the background color of the cells to clearColor if you use the tableView in grouped mode:

cell.backgroundColor = [UIColor clearColor];

Fourth implement the appropriate ScrollViewDelegate method of the TableView (scrollViewDidScroll). Notice that I modified the parameter to UITableView instead of UIScrollView. This is not necessary but makes to code more clear and you don’t have to cast a lot. We should calculate the correct position by the proportion of the contentSize of the TableView and the ScrollView.

// cheat a bit: modify the parameter to UITableView from UIScrollView
- (void)scrollViewDidScroll:(UITableView *)aTableview {

    if (aTableview != myTableView) {
        return;
    }
    UIScrollView *backgroundScrollView = (UIScrollView*)aTableview.backgroundView;

    // calculate the position of the scroll regarding to the position of the tableview
    float diffTableView = aTableview.contentSize.height - aTableview.frame.size.height;
    if (diffTableView>0) {
        float diffScroll = backgroundScrollView.contentSize.height - backgroundScrollView.frame.size.height;
        float newOffset = aTableview.contentOffset.y * (diffScroll/diffTableView);

        backgroundScrollView.contentOffset = CGPointMake(backgroundScrollView.contentOffset.x, newOffset);
    }
}

 

Notes: The image should be long enough to see the correct effect.

If you put a frame around your content you should play with margins and spacings:  you have to set up a header and footer and indent of each cell.

If you use sections take care of indenting the sections as well. You can achieve by implementing the  tableView:viewForHeaderInSection and return a UIView which contains a UILabel indenting appropriately.

You can set a semitransparent background color for each cell and/or you can use a faded image.

Download the sample project:

TableViewAutoScrollingBackground.zip