Ios – UIScrollView and setContentOffset

cocoa-touchiosiphoneuiscrollview

My question is about this method:
(void)setContentOffset:(CGPoint)contentOffset animated:(BOOL)animated

I have read the documentation, but i don't understand what this method is for.

thanks for your answers.

Best Answer

UIScrollView lets you have content that is larger than what you can view on the screen. In the image below you can see a large red rectangle with a green rectangle inside.

The contentArea property of the UIScrollView defines the logical size of your view (the red rectangle). The visible area of the scroll view is represented by the green rectangle. The contentOffset is the upper left corner of the visible area. Changing contentOffset, the visible area will move around.

(void)setContentOffset:(CGPoint)contentOffset animated:(BOOL)animated

The method above will move the contentOffset (the upper left corner of the green rectangle) to a specified location, thus moving the visible area (the green rectangle).

Hope this helps.

enter image description here

Related Solutions

Ios – Constants in Objective-C

You should create a header file like

// Constants.h
FOUNDATION_EXPORT NSString *const MyFirstConstant;
FOUNDATION_EXPORT NSString *const MySecondConstant;
//etc.

(you can use extern instead of FOUNDATION_EXPORT if your code will not be used in mixed C/C++ environments or on other platforms)

You can include this file in each file that uses the constants or in the pre-compiled header for the project.

You define these constants in a .m file like

// Constants.m
NSString *const MyFirstConstant = @"FirstConstant";
NSString *const MySecondConstant = @"SecondConstant";

Constants.m should be added to your application/framework's target so that it is linked in to the final product.

The advantage of using string constants instead of #define'd constants is that you can test for equality using pointer comparison (stringInstance == MyFirstConstant) which is much faster than string comparison ([stringInstance isEqualToString:MyFirstConstant]) (and easier to read, IMO).

Ios – How to sort an NSMutableArray with custom objects in it

Compare method

Either you implement a compare-method for your object:

- (NSComparisonResult)compare:(Person *)otherObject {
    return [self.birthDate compare:otherObject.birthDate];
}

NSArray *sortedArray = [drinkDetails sortedArrayUsingSelector:@selector(compare:)];

NSSortDescriptor (better)

or usually even better:

NSSortDescriptor *sortDescriptor;
sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"birthDate"
                                           ascending:YES];
NSArray *sortedArray = [drinkDetails sortedArrayUsingDescriptors:@[sortDescriptor]];

You can easily sort by multiple keys by adding more than one to the array. Using custom comparator-methods is possible as well. Have a look at the documentation.

Blocks (shiny!)

There's also the possibility of sorting with a block since Mac OS X 10.6 and iOS 4:

NSArray *sortedArray;
sortedArray = [drinkDetails sortedArrayUsingComparator:^NSComparisonResult(Person *a, Person *b) {
    return [a.birthDate compare:b.birthDate];
}];

Performance

The -compare: and block-based methods will be quite a bit faster, in general, than using NSSortDescriptor as the latter relies on KVC. The primary advantage of the NSSortDescriptor method is that it provides a way to define your sort order using data, rather than code, which makes it easy to e.g. set things up so users can sort an NSTableView by clicking on the header row.