Tài liệu Thủ thuật lập trình cho iPhone part 9 pdf

Make sure that you have completed the following tutorials before you begin this one:  iPhone Programming Tutorial – Creating a ToDo List Using SQLite Part 1  iPhone Programming Tutoria

Bài 10: Creating a ToDo List Using

SQLite Part 4

This is the final installment of our 4 part series of creating a Todo list for the

iPhone In this tutorial, I will detail how to add and delete new todo objects

from the SQLite database Make sure that you have completed the

following tutorials before you begin this one:

 iPhone Programming Tutorial – Creating a ToDo List Using SQLite Part 1

 iPhone Programming Tutorial – Creating a ToDo List Using SQLite Part 2

 iPhone Programming Tutorial – Creating a ToDo List Using SQLite Part 3

When you have completed this tutorial, you should have a main screen that

looks something like this:

Let‟s get started…

RootViewController.m and add the following code to the viewDidLoad

method

The first thing we see is the line that sets the leftBarButtonItem to

self.editButtonItem This automatically adds the “Edit” button to the

NavigationController Also, it sets up the functionality that allows the

“delete” buttons to be displayed when the button is pressed You can see

this functionality if you do a “Build and Go” at this step Next, I have

manually created a UIBarButtonItem and added it to the navigationbar This

can be done in Interface Builder, but I wanted to show you how to do it

manually and assign an action to it (I‟m sure you will require this

functionality in a future program) Here is a break down of the parameters:

 initWithTitle – The text to be displayed on the button

 style – How the button will look

 target – The class object that handles the messages sent from this button

 action – The method to be called when the button is passed We can use

@selector and give it the name of the function to call

Finally, we assign this button to the rightBarButtonItem If you do a Build

and Go, it should error since we haven‟t created the addTodo method We

will do that in a bit Now, let‟s create a method inside of our Todo object

that will add new Todos to the database

Open up Todo.h and add the following code:

So in addition to the insertNewTodoIntoDatabase method, we also see

the deleteFromDatabase method signature I have just added this so I don‟t

have to come back to it later We will be implementing this when I show you

how to delete todos from the database One thing to note about the

insertNewTodoIntoDatabase method is it has a “+” rather than a “-” sign

This means that it is a static method Static methods are associated with

the class not the instance meaning we can call this method without

instanciating this class So we can do stuff like

Todo.insertNewTodoIntoDatabase Now we will implement this method

Before we can do this, we must declare a few more static

sqlite3_statement‟s Add the following statements to the top of Todo.m

Nothing new here…Now implement the following method:

This is similar to our update method Notice that we are inserting default

values into the database This is so we don‟t run into any problems with null

or nil values The most important part of this method is the fact that it

returns the primary key of the newly created todo object This will be used

later so we can immediately transition to the todo when the “Add” button is

pressed The last thing we need to do to the todo object is update the

dehydrate method so that the todoText gets saved if it gets changed

Update the dehydrate method to look like this:

There are only a few minor changes here First we see the “text = ?” part

added to the sql statement This is simply so we can update the text of the

todo The other change is we bound the self.text property to the 1st

question mark in the sql statement One thing to notice is we call [self.text

UTF8String] This is because sqlite3_bind_text takes a (char *) This will

convert an NSString to an acceptable format

Now we need to add a method inside of our RootViewController to add a

todo This is the method that will be called when the user presses the “Add”

button Inside of RootViewController.m add the following code:

First, we get a reference to the appDelegate object This is because we

need to call its addTodo method Next, we instantiate the

TodoViewController if it has not already been instantiated We need this

around because we will push it on to the view stack and transition to it after

we create our new todo object After this is done, we call the addTodo

method of the appDelegate It will return the newly created todo object and

the view will be transitioned to its detail screen in order to update its details

Now we need to implement the method addTodo inside of our

appDelegate Open up todoAppDelegate.h and add the following code to

create the method signature

Now, let‟s implement this method Open up todoAppDelegate.m and add

the following code:

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First, we are calling the insertNewTodoIntoDatabase method of the Todo

object Notice that we are simply calling the method without first building an

instance of a todo object As I said in tutorial 3, this is because that method

is static and gets called without building an instance of the class Next, we

insatiate the todo object that was just created by calling its

initWithPrimaryKey method This will give us reference to the new todo

object Finally, we append this todo to the end of our todos array Since our

UITableView is updated with this array, it will automatically include the new

todo object The last line just returns this todo object

Remember is the last tutorial we made it so the users could update the

status and the priority of a todo? Well, now we also need to give them the

ability to update the text of the todo So open up TodoViewController.h and

add the following code:

Ok, so I‟m guessing you are wondering why the UITextView for the

todoText object has been changed to a UITextField Well, I will tell you

UITextView doesn‟t have the methods that we need to save the text with

our current design We will also be changing this on our Interface inside of

Interface Builder So for now, just believe me and anywhere it says

UITextView, change it to UITextField The only additional code we added

here is the method signature for the updateText method It‟s an IBAction

that will get called when the user presses the “Done” button on the

keyboard after setting the text for the todo Next, we need to implement this

method Open up TodoViewController.m and add the following code:

All this does is update the text of the todo to the text that the user entered

inside of the UITextField The last thing we need to do in order to add a

todo is to replace the UITextView with a UITextField and connect it to our

updateText method Double click on your TodoViewController.xib file to

open it in Interface Builder

Now click on the UITextView on your interface and press the delete key on

your keyboard to delete it Now, drag a UITextField from the library and

drop it onto your interface Resize it to fit When you have completed that,

your interface should look something like this:

Now we need to connect this component Make sure it is selected and click

Tools -> Connections Inspector to open up the connections inspector Drag

from the circle next to the method “Did End On Exit” to the “File‟s Owner”

object The words udpateText should pop up Click on them to make the

connection Next, click in the circle next to “New Referencing Outlet” and

drag it to the “File‟s Owner” object Select todoText when it pops up The

Connections Inspector should look like this:

Now we are done with Interface Builder Go ahead and close it We are

now able to add todos The last thing we need to do is give the ability to

delete todos from the list as well as our database This is all done in code,

and we won‟t need interface builder for this

Let‟s start by adding the methods to the appDelegate to handle the deletion

of todos Open up todoAppDelegate.h and add the following code:

All we see here is a signature for the removeTodo method Also, be sure to

add a #import “Todo.h” statement to the top of this file so that we can

interface with the todo objects Now let‟s implement the removeTodo

method Open up todoAppDelegate.m and add the following code:

The first line looks up the todo in the todos NSArray It returns the index in

the array of the todo to be deleted Then, we call the deleteFromDatabase

method on the todo object and then remove it from the todos array Since

the UITableView is updated via this array, it will automatically remove the

todo without any additional code on our part

Now, let‟s create the removeTodo method for the todo object We have

already written the method signature in Todo.h in a previous step, so open

up Todo.m and add the following code:

Remember the delete_statement variable is a static sqlite3_stmt that we

we just step the statement to execute it and reset it The last thing we need

to do to delete todos from the database is to specify what happens when

the user presses the “delete” button Open up RootViewController.m and

add the following code:

The first step (like the first step of many functions) is to get a reference to

the appDelegate Next, we check to see if we are currently editing If so,

call the removeTodo method on appDelegate The next line, removes the

row from the UITableView at the given indexPath

Now click Build and Go! You should now be able to add and delete todo

items from the database This concludes our four part series of creating a

todo list for the iPhone As always, if you have any questions feel free to

leave them in the comments section If you get lost at any time you can

download the sample code here

Bài 11: UITabBar iPhone Tutorial

Phần này hướng dẫn cách sử dụng UITabBar

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This tutorial will show you the basics of using the UITabBar and

UITabBarItem controls when programming for the iPhone

I will be showing you step by step in the video how to create a project from

a UITabBar template and add additional UITabBarItems as well as

additonal views to be displayed with these items Here is a brief

explanation of each step:

1 Create a new project from a UITabBar template

This is pretty straight forward We will be using Apple‟s default UITabBar

template to start our project This is a fully functioning app You can click

Build and Go to see it run

2 Open Interface Builder (click on mainWindow.xib) and Add

addtional UITabBar items

To add additonal UITabBarItems, you simply drag them from the library on

to the UITabBar For each new item, you must specify the name of the view

that will be shown when the item is clicked This is done by clicking on the

tab bar item and clicking Tools -> attributes inspector There should be a

box titled “Nib Name” Whatever you enter here will be the name of the

view that will be loaded when this tab is clicked

So for this tutorial, we entered ThirdView So, naturally when we created

our view to be loaded here, we saved it as “ThirdView.xib” This is one

Gotcha when working with these components

This is took me a while to figure out To change the text, image, or style of

the UITabBarItem, double click on it You should now be able to access

these settings in the Attributes Inspector

4 Set the Background Color For Views 1 and 2

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This was pretty easy For the first view, we simply clicked on it and clicked

the box next to “Background” in the Attributes Inspector Next, we did the

same to the secondView by opening up SecondView.xib in Interface

Builder

5 Create ThirdView

We need to create the third view to be loaded when the user clicks on the

UITabBarItem that we inserted This was done inside of Interface Builder

by clicking File -> new and selecting View The next thing we did was drag

a label from the library and add it to the view Finally, we set the

background color like we did in the other views

Be sure when you save this view, you name it ThirdView.xib (this

corrisponds the name that we put in the “Nib Name” box in step 2) Also, be

sure to save this view in your projects folder (sometimes Interface Builder

does not navigate here by default)

6 Connecting ThirdView to the ViewController

In this step we connect the ThirdView to our FirstViewController Notice

that all of the views get connected to this view controller This will handle all

of the UI components put on to each view *Note: this step can‟t be done

until ThirdView is saved and added to the project

So to connect this view to FirstViewController, simply click on the File‟s

Owner object and select FirstViewController from the drop-down in the

Identity Inspector

The last thing we need to do is connect the view So control-click from

File‟s Owner and drag the line to the View object The word “View” should

pop up Click on it and the views are now connected

That should be it! Click Build and Go and you are done

Well, I hope you guys have enjoyed the video tutorial I know that the audio

is kind of low This is because I used my computer‟s built in microphone

and it‟s not the greatest I have since purchased a new microphone (thanks

again to all who have donated thus far) and future tutorials will have much

better audio quality I would LOVE to hear your feedback on the videos I‟m

a total noob when it comes to screencasts and would love your