head first iphone development a learners guide to creating objective c applications for the iphone 3 phần 3 potx

you are here 4 91objective-c for the iPhone We’ll put the text field in here Scoot this stuff down a little Code Magnets Using what you know from adding the picker and the button, match

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you are here 4 77

iPhone app patterns

@ synthesize goes along wi th the

@property declaration in the h file See Chapter 3 f or more info

The last thing you need to do with tweetPicker is release our reference to it - another memory thing We’ll come back to the memory management in Chapter 3, we promise

InstatwitViewController.m and then add the implementation.

What’s next?

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connect the outlet to the code

Connect the picker to our outlet

You’re probably expecting this by now! Back into Interface Builder to

make the connection from the UIPickerView to the IBOutlet in our

view controller Right-click on the UIPickerView, grab the circle next

to the “New Referencing Outlet,” and drop it on File’s Owner—our

InstatwitViewController sporting its new tweetPicker outlet

When you click and drag up to

File’s Owner, you will be able to

connect it to the tweetPicker

outlet you just created.

What do you need to do now to get the data out of the picker and into your Twitter message? Think about the “Tweet it!” button press action and how that will need to change

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Use our picker reference to pull

the selected values

Now all that’s left is to use our reference to the picker to get

the actual values Mike selects We need to reimplement the

sendButtonTapped method to pull the values from the

picker Looking at the UIPickerView documentation, the

method we need is selectedRowInComponent: That

method returns a row value, which, just like before, we can

use as an index into our arrays

- (IBAction) sendButtonTapped: (id) sender {

NSString* themessage = [NSString stringWithFormat:@”I’m %@ and feeling %@

about it.”,

[activities objectAtIndex:[tweetPicker selectedRowInComponent:0]], [feelings objectAtIndex:[tweetPicker selectedRowInComponent:1]]]; NSLog(themessage);

NSLog(@”Tweet button tapped!”);

the picker the “%@” in the s tring format get

replaced with the values w e pass in.

To figure out what Mike chose on the picker, we need to ask the picker wha t row

is selected, and get the corr

esponding string from our arrays.

We’re just going to log this message to the console so we can see the string we’re building, and then we’ll send this to Twitter in just a minute Let’s make sure we implemented this correctly first before tweeting to the whole world

ters, integers, etc., but for now we jus t need to insert the t

wo selected strings, so we’ll use %@.

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Ready Bake

Code

//TWITTER BLACK MAGIC

NSMutableURLRequest *theRequest=[NSMutableURLRequest requestWithURL:[NSURL URLWithString:@”http://YOUR_TWITTER_USERNAME:YOUR_TWITTER_PASSWORD@twitter.com/

statuses/update.xml”]

cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:60.0];

// END TWITTER BLACK MAGIC

To post to Twitter, we’re going to use their API Rather than

go into a Twitter API tutorial, we’ll give you the code you need to tweet the string Type the code you see below into the InstatwitViewController.m, just below the NSLog with the Twitter message in the sendButtonTapped method

Your username and password need to go in here.

If you don’t have a Twitter account, just go get one!

Just go to twitter.com and register Once you do that, you can enter your username and password, and this will work like a charm

After adding that code, you can just save, build and go It will

now show up on your Twitter feed Go ahead, try it out!

InstatwitViewController.m

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mike’s feeling great about your app

That is great! Now, Renee is happy and feels included and I don’t actually have to talk out loud about my feelings At all Ever.

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iPhonecross

Flex your vocab skills with this crossword Untitled Puzzle

Header Info 1Header Info 2

3 This typically handles the information itself in the app

6 This is the document Apple uses to evaluate apps for

the App Store

7 You see this listed in the view and it controls the view

9 This component allows for controlled input from several

selections

10 This type of app is typically one screen, and gives you the

basics with minimal interaction

11 These define to which messages the datasource and

4 This app type typically involves hierarchical data

5 This app type is mostly custom controllers and graphics

8 The other name for an *.xib file

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more app types

We’ve listed a couple of descriptions of a some different apps Using the app description, sketch out a rough view and answer the questions about each one

Generic giant button app

There are several of these currently up for sale

on the app store This app consists of pushing

a big button and getting some noise out of your iPhone

1

What type of app is this?

What are the main concerns in the HIG about this app type?

Book inventory app

This app’s mission is to keep a list of the books

in your library, along with a quick blurb of what it’s about and the author

2

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iPhonecross Solution

Flex your vocab skills with this crossword

Untitled Puzzle

Header Info 1Header Info 2

6 This is the document apple uses to evaluate apps for the

App Store [HUMANINTERFACEGUIDE]

7 You see this listed in the view and it controls the view

[FILESOWNER]

9 This component allows for controlled input from several

selections [PICKER]

10 This type of app is typically one screen, and gives you the

basics with minimal interaction [UTILITY]

11 These define to which messages the datasource and

delegate respond [PROTOCOLS]

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exercise solution

We’ve listed a couple of descriptions of a some different apps

Using the app description, sketch out a rough view and answer the questions about each one

Generic giant button app

There are several of these currently up for sale

on the app store This app consists of pushing

a big button and getting some noise out of your iPhone

1

Book inventory app.

This app’s mission is to keep a list of the books

in your library, along with a quick blurb of what it’s about and the author

2

Bug button that you push

Just one view

An immersive app

The big thing Apple cares about is that controls “provide an internally consistent experience.” So everything can be custom, it needs to focused and well organized.

A productivity app

The HIG has many more specific rules about this app type, because you’ll be using standard controls EACH control needs to be checked out for proper usage

Another view for details, need to figure out how to get to it

Book list

Some navigation stuff here

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Your iPhone Toolbox

You’ve got Chapter 2 under

your belt and now you’ve

added protocols, delegates, and

datasources to your toolbox For a

complete list of tooltips in the book,

In a picker, each dial is a component

In a picker, each item is a row

Protocols define the messages your class must realize—some of them might be optional

Protocols

Define the messages y our

datasource and delega te must

Works with databases, plis ts, images, and other genera l info that your app will need t o display

Can be the same objec t as a delegate, but has i ts own specific protocols.

Can be in same objec t as the datasource, but has i ts own specific protocols.

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renee is getting suspicious

This is Renee, Mike’s

girlfriend

It’s so great that Mike and I are communicating now! But I’ve noticed that Mike’s starting to sound like he’s in a rut, saying the same thing over and over again! Is there something we need to talk about?

Sounds like Mike is going

to need some modifications

to InstaTwit to keep his relationship on solid ground

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this is a new chapter 89

I know these are letters and

all, but I have no idea what

you’re saying

objective-c for the iPhone

3

Twitter needs variety

We did a lot in chapter 2, but what language was that?

Parts of the code you’ve been writing might look familiar, but it’s time you got a sense of

what’s really going on under the hood The iPhone SDK comes with great tools that mean

that you don’t need to write code for everything, but you can’t write entire apps without

learning something about the underlying language, including properties, message passing,

and memory management Unless you work that out, all your apps will be just default

widgets! And you want more than just widgets, right?

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renee wants more

InstaTwit was working great, and is so easy to use! But I think Renee is on to me She said I sound like I’m in a rut I need to be able to add to my tweets

or this isn’t going to work much longer

Renee is catching on

Mike has been diligently using InstaTwit to communicate his feelings, but his girlfriend is starting to think something weird is going on Even for Mike, who

is a guy who likes his routines, his tweets are starting to sound suspicious

We need to make some adjustments

to our InstaTwit design

Take a look at the various UI controls available in

Interface Builder, and think about what would be a

quick and easy way for Mike to add to his tweets.

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objective-c for the iPhone

We’ll put the text field in here

Scoot this stuff down a little

Code Magnets

Using what you know from adding the picker and the button, match the

magnet with the method or file that you’ll need to edit to add the text field

Add an IBOutlet and @property

declaration for the UITextField

Add [notesfiel d release] Link the UITextField

to the dealloc in InstatwitViewController.m

using Interface Builder

to the property created in step

#1, using Interface Builder

Create a deleg ate and datasource for

the notesField

Add an IBAction for the UITextField

Make room for custom input

It’s nothing fancy, but Mike could add a little personal flavor to his

tweets with a text field at the start It means he’ll need to do some

typing, but in the end his tweets will be more unique

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IBOutlet UIPickerView *tweetPicker;

IBOutlet UITextField *notesField;

NSArray* activities;

NSArray* feelings;

}

@property (nonatomic, retain) UIPickerView* tweetPicker;

@property (nonatomic, retain) UITextField* notesField;

design magnets solution

Design Magnets Solution

Add an IBOutlet and @property declaration for the UITextField

Wait a minute We keep adding code to this h file, but I still don’t know what a h file really does!

What gives?

A h file is a header file.

It’s where you declare the interface and methods for a class All

of the classes we’ve used so far, like UITextField, NSString, and NSArray, have header files you can look through Take a minute to look through a couple and start thinking about what is happening

in those files

Beware of private framework headers

Sometimes you’ll come across a really tempting method that’s not defined in the Apple Documentation Using undocumented APIs will get your app rejected from the iTunes store.

InstatwitViewController.h

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- (IBAction) sendButtonTapped: (id) sender;

Here’s our current InstatwitViewController.h file Fill in the

blanks and explain what each line does.

#import <UIKit/UIKit.h>

@interface InstatwitViewController : UIViewController

<UIPickerViewDataSource, UIPickerViewDelegate> {

IBOutlet UITextField *notesField;

NSArray* activities;

NSArray* feelings;

}

@property (nonatomic, retain) UITextField* notesField;

- (IBAction) sendButtonTapped: (id) sender;

- (IBAction) textFieldDoneEditing:(id) sender;

@end

Header files describe the interface to your class

In Objective-C, classes are defined with interfaces in the header file It’s where you declare if your

class inherits from anything, as well as your class’ fields, properties, and methods

IBOutlet UIPickerView *tweetPicker;

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IBOutlet UITextField *notesField;

This is where we can declare fields of our class.

Here’s our inheritances and interfaces

It’s almost identical to C’s #include,

except that it automatically prev ents

including the same header multiple

times (so no more #ifndef

MY_HEADER).

@interface indicates you’re

going to declare a class.

Next comes the class name, and

if it inherits from something then a colon and the sup

er class’s name.

Any protocols you implement go in angle brackets separa ted by commas

Protocols are like Java interfaces or pure virtual classes in C++, and a cl ass

can realize as many as you want.

IBOutlet allows Interface Builder t o

recognize fields that you can attach t o

controls (like our notes field in Ins taTwit).

The syntax for fields is just like in C++: Basic types like int and float are used

as is; pointer types use an asterisk By default, all fields are given protec ted access, but you can change tha t with

@private or @public sections simil ar to C++.

Objective-C doesn’t support multiple inheritance

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@property (nonatomic, retain) UITextField* notesField;

- (IBAction) sendButtonTapped: (id) sender;

- (IBAction) textFieldDoneEditing:(id) sender;

@end

Once you’ve closed the field section of your interface, you can declare properties @property tells Objective-C to autogenerate getter and setter methods for you.

The @property keyword tells the

compiler this is a property that will be

backed by getter and (maybe) setter

These are the method declarations.

@end: ends your class interface declaration.

The minus sign means it’s an instanc e

method (a + means it’s static) All

methods in Objective-C are public.

IBAction lets Inter face

Builder identify methods

that can be attached t o

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@synthesize tweetPicker, notesField;

magnets solution

Design Magnets Solution (Continued)

OK, so if we declared a property

in the h file, then adding @synthesize

in the m file must auto-generate some code, right?

Yes! It generates the getter and setter methods.

Using @property lets the compiler know we have a property,

but that’s not enough Using the @synthesize keyword in the

implementation files, we can have the compiler auto-generate the

setter and getter method we talked about earlier The compiler will

generate a getter, and, if it’s a readwrite property, a setter and

implement it based on the @property attributes declared in the h

file So what do the different @property attributes do ?

Back in that design we were working on

@property (nonatomic, retain) UITextField* notesField;

Add an IBOutlet and @property declaration for the UITextField

InstatwitViewController.m

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When you want the property to be modifiable by people The compiler will generate a getter and a setter for you This is the default.

readonly

Below is a list of the most commonly used property attributes and

definitions Match each attribute with its definition

When you’re dealing with object values The compiler will retain the value you pass in (we’ll talk more about retaining in a minute) and release the old value when a new one comes in.

When you don’t want people modifying the property You can still change the field value backing the property, but the compiler won’t generate a setter.

When you want to hold onto a copy of some value instead of the value itself; for example, if you want

to hold onto an array and don’t want people to be able

to change its contents after they set it This sends a copy message to the value passed in then retains that.

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who does what solution

When you want the property to be modifiable by people The compiler will generate a getter and a setter for you This is the default.

When you’re dealing with object values The compiler will retain the value you pass in (we’ll talk more about retaining in a minute) and release the old value when a new one comes in.

When you don’t want people modifying the property You can still change the field value backing the property, but the compiler won’t generate a setter When you want to hold onto a copy of some value instead of the value itself; for example, if you want

to hold onto an array and don’t want people to be able

to change its contents after they set it This sends a copy message to the value passed in then retains that.

SOlUTion

Q: How does the compiler know what field to use to hold the

property value?

A: By default, the compiler assumes the property name is the

same as the field name In reality, it doesn’t have to be You can

specify the field to use to back a property when you @synthesize it

like this: @synthesize secretString=_superSecretField;.

Q: What about that nonatomic keyword?

A:By default, generated accessors are multithread safe and use mutexes when changing a property value These are considered atomic However, if your class isn’t being used by multiple threads, that’s a waste You can tell the compiler to skip the whole mutex thing

by declaring your property as nonatomic.

Below is a list of the most commonly used property attributes and definitions Match each attribute with its definition

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Auto-generated accessors also handle memory

management

Objective-C on the iPhone doesn’t have a garbage collector, so you have to use reference counting

That involves keeping up with how many references there are to an object, and only freeing it up

when the count drops to zero (it’s no longer being used) When you use properties, the compiler

handles it for us The properties we’ve declared so far have all used the retain attribute When the

compiler generates a setter for that property, it will properly handle memory management for us,

Here the compiler jus t returns the value, nothing exci ting.

Since we didn’t say the prop erty

is readonly, the comp iler will generate a setter f or us

Since we used the r etain keyword, the generated setter check s to make sure the new value is dif ferent, then does

a release on the old v alue and a retain

on the new one.

1 @property (nonatomic, readonly) NSString* myField

2 @property (nonatomic, retain) NSString* myField

3 @property (nonatomic, assign) NSString* myField

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sharpen solution

1 @property (nonatomic, readonly) NSString* myField

2 @property (nonatomic, retain) NSString* myField

3 @property (nonatomic, assign) NSString* myField

However, for basic types like booleans and f loats, you can’t do reference counting Assignment is almost always what you want

Below is the code that the compiler will generate for each property.

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you are here 4 101

I bet that release just lets go of the memory that your properties use up, right?

Objective-C can automatically release references, too.

In addition to retain and release, Objective-C has the concept of an autorelease pool This is basically an array of objects that the runtime will call release on after it’s finished processing the current event To put something in the autorelease pool, you simply send it the autorelease message:

[aString autorelease];

It will still have the same retain count, but after the current event loop finishes, it will be sent a release You won’t want to use this all the time because it’s not nearly as efficient and has some performance overhead It’s not a bad thing to use, but it’s better to explicitly retain and release when you can

You must release objects you create with alloc, new, copy, or mutableCopy

If you create an object with alloc, new, copy, or mutableCopy, it will have a retain count of 1

and you’re responsible for sending a release when you’re done with the object You can also

put the object in the autorelease pool if you want the system to handle sending a release later

1

Consider everything else to have a retain count of 1 and in the autorelease

pool.

If you get an object by any other means (string formatters, array initializers, etc.) you should

treat the object as having a retain count of 1 and put it in the autorelease pool This means

that if you want to hang onto that object outside of the method that got the object, you’ll

need to send it a retain (and a corresponding release later)

2

To keep your memory straight, you need to

remember just two things

Memory management can get pretty hairy in larger apps, so Apple has a couple of

rules established to keep track of who’s in charge of releasing and retaining when

Get it? Memory, remember?

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memory management up close

Memory Management Up Close

- (void)dealloc {

[tweetPicker release];

[activities release];[feelings release];

[super dealloc];

}

Memory management is definitely important on iPhone, but that doesn’t mean it’s

complicated Once you get the hang of a few key principles, you’ll be able to structure

your app so that it doesn’t leak memory and get you kicked out of the app store

When you create an object, it starts with a count of 1, and different things you do can

raise and lower the count When the count reaches 0, the object is released and the

memory is made available

This is some of the memory management code that YOU have already written!

NSString *aString = [[NSString alloc] init];

1

2

1 2

At first, ther e’s no

memory alloca ted

when you alloc a cl ass, the reference count is set to 1.

Each retain ca ll adds one

to the count

and a release ca ll subtracts one.

If another objec

t (like this array) needs t

o hang onto your objec t,

it will retain it

and release i ts reference when it’s done wi th it.

Once the count gets t o 0, the object’s dea lloc is called and the memory is f reed.

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you are here 4 103

Determine how many references are left at the end of the chunk of code and if

we have to send it a release for each string

NSString *first = [[NSString alloc] init];

NSString *second = [[NSString alloc] init];

[someStringArray addObject:second];

NSString *third = [[NSString alloc] init];

[third autorelease];

NSString *fourth = [NSString

stringWithFormat:@”Do not read %@”, @”Swimming

with your iPhone by TuMuch Monee”];

NSMutableArray *newArray = [[NSMutableArray alloc] init];

NSString *fifth = [[NSString alloc]

initWithFormat:@”Read this instead: %@”, “Financing your

iPhone 4G by Cerius Savar”];

[newArray addObject:fifth];

[newArray release];

NSString *sixth = [NSString stringWithString:@”Toughie”];

NSArray *anotherArray = [NSArray

arrayWithObjects:sixth count:1];

NSDictionary *newDictionary = [NSDictionary

dictionaryWithObjects:sixth forKeys:@”Toughie”

count:1];

NSString *ignoreMe = [sixth retain];

Final Reference Count

Tiêu đề	iPhone App Patterns
Trường học	University of Technology
Chuyên ngành	Computer Science
Thể loại	Hướng dẫn
Năm xuất bản	2025
Thành phố	Hanoi

Định dạng
Số trang	54
Dung lượng	1,8 MB