Swipe 2011 - iOS Gems

iOS Gems
Some jewels for your glory box

Kevin O’Neill
Delivery Manager – Mobile
REA Group
twitter: @kevinoneill

This is not a con dential session — please stream, blog, tweet and take pictures :)

Roadmap
• Enhancing NSArray

• View size and layout

• Simple gestures handling

• Closing thoughts

It’s verbose
- (NSIndexSet *)indexesOfObjectsWithOptions:
(NSEnumerationOptions)opts passingTest:(BOOL
(^)(id obj, NSUInteger idx, BOOL *stop))
predicate

Difﬁcult to combine
- (NSIndexSet *)indexesOfObjectsAtIndexes:
(NSIndexSet *)indexes options:
(NSEnumerationOptions)opts passingTest:(BOOL
(^)(id obj, NSUInteger idx, BOOL
*stop))predicate;

We Can Do Better
• Enumeration

• Filtering

• Transformation

Enumeration
- (void)each:
(void (^)(id item))block;

- (void)eachWithIndex:
(void (^)(id, NSUInteger))block;

Enumerations produce no
‘value’

They mutate state of the
world around them

EG
NSMutableSet *uniqueNames = [NSMutableSet
set];
[names each: ^ (id name) {
[uniqueNames addObject:name];
}];

OR
[[view subviews] eachWithIndex:^ (id subview,
NSUInteger position) {
CGRect cell_frame =
CGRectMake(subview_width * position,
0,
requested_subview_size.width,
requested_subview_size.height);

Demo
Enumeration
Use and implementation

A for loop may often be a
better choice

Useful at the tail of
transform operations

Filtering
- (NSArray *)filter:(BOOL (^)(id item))block;

- (NSArray *)pick:(BOOL (^)(id item))block;

- (id)first:(BOOL (^)(id))block;

- (id)last:(BOOL (^)(id))block;

Filter removes matching
elements

Filter
NSArray *names = [NSArray arrayWithObjects:
@"Kevin", @"Sue", @"Aaron",
@"Jack", @"Maddie", nil];

[[names filter:^BOOL(id name) {
return [name length] < 5;
}] each:^(id name) {
NSLog(@"%@", name);
}];

"Kevin"
"Aaron"
"Maddie"

Pick selects matching
elements

Pick

[[names pick:^BOOL(id name) {
}] each:^(id name) {
NSLog(@"%@", name);
}];

"Sue"
"Jack"

First returns the ﬁrst
element matched

First

NSLog(@"%@", [names first:^BOOL(id name) {
}]);

"Sue"

Last returns the last
element matched

Last

NSLog(@"%@", [names last:^BOOL(id name) {
}]);

"Jack"

Demo
Filter, Pick, First and Last

Transformation
- (NSArray *)map:(id (^)(id item))block;

- (id)reduce:(id (^)(id current, id item))block
initial:(id)initial;

- (NSArray *)intersperse:(id (^) (void))separator;

Map applies the block to
each element

Map

[[names map:^id(id name) {
return [NSNumber numberWithInteger:
[name length]];
}] each:^(id length) {
NSLog(@"%@", length);
}];

"5"
"3"
"5"
…

Reduce applies the block
to each element passing
the result along

Reduce

NSLog(@"%@",
[names reduce:^id(id current, id item) {

NSInteger result = [current integerValue]
+ [item length];
return [NSNumber numberWithInteger:result];

} initial:[NSNumber numberWithInteger:0]]);

"23"

Place the result of the
block between elements

Intersperse

[[names intersperse:^id(id current, id next) {
return [current length] > [next length]
? @">" : @"<";
}] each:^(id item) {
NSLog(@"%@", item);
}];

"Kevin"
">"
"Sue"
"<"
…

Demo
Map, Reduce, Intersperse

How to size and layout
subviews without pain

I’m an interface builder
muppet

Two methods are key
- (void)layoutSubviews;
- (CGSize)sizeThatFits:(CGSize)size;

sizeThatFits: and
layoutSubviews are loosely
paired

They must be sympathetic
to one and other


• Does nothing by default
• Used to position subviews
• Called when the layout is dirty
• Don’t call it manually– I’ve seen to
many times

• Don’t resize self – I’ve seen to many
times

- (CGSize)sizeThatFits:
(CGSize)size;

• Returns current size by default
• Return ‘best’ size to ﬁt given size
• Doesn’t resize the view
• Don’t resize the view – I’ve seen to
many times

• Don’t layout view – I’ve seen to many
times

The calculations used are
often the same, just
applied differently

EG
- (CGSize)sizeThatFits:(CGSize)size;
{
float width = size.width;

float height = [[[self subviews] reduce: ^ id (id current, id item) {
CGSize item_size = [item sizeThatFits:CGSizeMake(width, 0.)];

return [NSNumber numberWithFloat:
ceilf([current floatValue] +
(item_size.height + [self spacingForSubview:item]))];

} initial:[NSNumber numberWithFloat:0.]] floatValue];

CGSize result = CGSizeMake(width, height);

return result;
}

And
{
float width = [self width];

__block StackedView *block_self = self;

[[self subviews] reduce: ^ id (id current, id item) {
CGSize item_size = [item sizeThatFits:CGSizeMake(width, 0.)];

[item setFrame:
CGRectMake(0,
[current floatValue] + [block_self spacingForSubview:item],
item_size.width,
item_size.height)];

return [NSNumber numberWithFloat:ceilf([item bottom])];
} initial:[NSNumber numberWithFloat:0.]];
}

The only real variance here
is the action

And that’s a simple
example

The layout algorithm is
coded once

But maintaining pairing
between selectors and
actions is a little tedious

EG
- (void)cancelRequest
{
[self displayCancelMessage];
}

UITapGestureRecognizer *tapRecognizer =
[[UITapGestureRecognizer alloc]
initWithTarget:self
action:@selector(cancelRequest)];

Can you guess what makes
gesture handling easier?

Blocks make gesture setup
much easier

Understanding blocks will
make you more productive

New Core API’s are taking
advantage of blocks

Categories are a key
method of partitioning
behaviour

Blocks are a key method of
partitioning algorithms

Associated objects should
be part of your toolkit

Don’t use these tools
because they are there

Use them to make your
code …

Useful Bits

Open source libraries used
https://github.com/kevinoneill/Useful-Bits
https://github.com/kevinoneill/Useful-Swipe
https://github.com/domesticcatsoftware/DCIntrospect

Questions?

Swipe 2011 - iOS Gems

Recommandé

Recommandé

Contenu connexe

Tendances

Tendances (20)

En vedette

En vedette (6)

Similaire à Swipe 2011 - iOS Gems

Similaire à Swipe 2011 - iOS Gems (20)

Dernier

Dernier (20)

Swipe 2011 - iOS Gems