Tài liệu Thủ thuật lập trình cho iPhone part 8 docx

For this tutorial, we will need to get the last variable from the todo database.. We need to get it from the database and associate it with the todo object.. updateStatus will be the met

Bài 9: Creating a ToDo List Using SQLite

Part 3 (go on)

This is part 3 in our multipart series of creating a todo list for the iPhone

For this, you must have completed the following tutorials

The focus of this tutorial will mainly be on viewing the todo items when

selected I will also show you how to update the todo status This will

require us to use interface builder When you are completed, you will be

able to edit todos through an interface similar to this:

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Bringing Your Code Up To Speed

For this tutorial, we will need to get the last variable from the todo

database This is of course being the status variable If you recall, it‟s a

boolean value (1 for complete, 0 for in progress) We need to get it from the

database and associate it with the todo object First let‟s create a property

to hold this value Open todo.h and add the following code:

So a few changes here…First there is the added NSInteger status This will

be the property we associate with the status (complete or not) of the todo

We also create a property from it Next, there is a BOOL property called

“dirty” We will use this object to signify when a todo has been altered You

will see how this comes into play when we implement the dehydrate

method Also, I have added 3 method signatures updateStatus will be the

method called when we want to update our status variable Similarly, the

updatePriority method will be called to update the priority Finally, we have

added a dehydrate method This method should be familiar (or confusing) if

you have messed with Apple‟s books example Basically, it will be used to

save the state of the todo to the database We will be calling this method

on each todo item when the program exits I will show you how to do this in

a little bit

Be sure to add the status variable to the synthesize line Also, as we did

before, we need to create a static sqlite3_stmt to hold the compiled

dehydration statement Add the following code to Todo.m:

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Now let‟s implement the methods Add the following code:

The first two methods (udpateStatus and updatePriority) are pretty strait

forward They update the status and the priority of the todo and then set the

“dirty” property to 1 This signifies that the todo has been altered and will

need to be saved to the database

Finally, there is the dehydrate method… We will call this method on each

todo upon termination of the program If the todo is “dirty” meaning the dirty

property was set to YES, we will need to save the new data to the

database The database code should look pretty similar to code in previous

tutorials First, we check to see if the dehydrate_statement is equal to nil If

you recall, this will only happen the first time this method gets called Next

we create the update statement and then bind our variables to each of the

“?”‟s Notice the ordering The numbers represent the question marks from

left to right (1 being the first, 2 being the second, 3 being the third) It took

me quite some time to figure this out Finally, we execute the sqlite

statement by calling sqlite3_step and then reset the statement

The last thing we need to do to Todo.m is change the SELECT statement

in the initWithPrimaryKey method to grab the „complete‟ field Update the

code to look like the screenshot below:

There are not really many changes The first change is the added status to

the synthesize line Next, the sql statement was updated to read

SELECT text,priority,complete FROM todo WHERE pk=?

This allows us to get the “complete” field from the database Finally, there

is the line “self.status = sqlite3_column_in(init_statement,2);” This is

assigning the status property to the data at index 2 in the sql data array

We can now use this field

One thing we need to do for the navigation to function properly is add a title

to our main view Open up rootViewController.m and add the following

code to the viewDidLoad method:

Create the Todo Detail View

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Now we are going to create the view that will display when the user selects

the todo in the UITableView Go ahead and open up Interface Builder by

selecting one of you existing nib (.xib) files Once it‟s open add a new View

by clicking File -> New and select View Drag the following controls

 UITextView

 UISegmentedControl – For this you will need to set the number of

segments to 3 You will also see a dropdown menu below this option

Select each segment and fill in one of the priorities for the title Here is a

screenshot You should give a title to each (Low , Medium, High)

 UILabel – This will be used to display the status

 UIButton – Users will click this button to update the status (Mark as

complete)

When you are done, your interface should look something like this (but

probably better):

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I know that my interface doesn‟t look the coolest I‟m a programmer not a

graphic designer… Ok save this view by pressing Command-S Make sure

you are in your current projects directory Name it TodoViewController

and press Save

It will then ask you if you want to add it to your project Check the box next

to the word todo and click Add

Now close Interface Builder Next, we are going to add the viewController

class and set up variables to interface with this view

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Create TodoViewController Class Files

Click File -> New File… Select UIViewController Subclass and click

Next

Name the file TodoViewController and make sure that the box that says

“Also create TodoViewController.h” is checked and click Finish

Open up TodoViewController.h and add the following code

Basically, we are setting up Interface Builder Outlets for each of the UI

components to be connected to Notice, the UIButton has an IBOutlet This

is because we will need to update the text on the button depending on

whether or not the todo is completed Also, I have an IBAction called

updateStatus We will be connecting this to the button we created It will

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toggle the status (pending/complete) of a todo item Finally, we see the

updatePriority method This method will be called when the user selects

one of the priority segments in the UISegmentedControl Next, open up

TodoViewController.m and add the following synthesize code:

50,336x280;ord=' + ord + '?"><\/script>'); //]]> </script>

This will allow us to get and set these variables

Before we connect this code to the Interface, we need to implement the

methods that will be called when the user presses the button to mark a

todo as complete as well as when the user presses a segment in the

UISegmentedControl Inside of TodoViewController add the following

methods

Let‟s go through this First we see the updateStatus method This gets

called when a user presses the button to alter the status We basically

check the current status of the todo (whether or not it‟s completed) and

depending on that, change the text to be displayed on the UIButton So, if

the todo is not complete (in progress) and this button is pressed, the text

will be changed from “Mark As Complete” to “Mark As In Progress” Finally,

we call the updateStatus of the todo and pass the new value (1 or 0) to it

Next we see the updatePriority method It simply reads the value of the

UISegmentedControl by calling the selectedSegmentIndex method on it

The next part looks a little messy There are 2 reasons that reason we can‟t

just pass the value of the UISegmentedControl directly to the method The

first is, the UISegmentedControl is ordered in acending order (1, 2, 3…),

but our priorities are in descending order (3 = low, 2 = medium, 1 = high)

This is where the “2 – priority” comes from Next, UISegmented controls

are “0 indexed” meaning the indices start at 0 and increment from there So

we need to add a “+1″ to the index as our todo priorities start at 1

Now we need to connect the UI Components in Interface Builder to this

code Double click on TodoViewController.xib to open it in Interface Builder

Connecting UI Components To Code

We first need to associate this view with the class we just created In the

Interface Builder, click on the File‟s Owner object Next click Tools ->

Identity Inspector You should see a drop-down next to class Select

TodoViewController from this list and you will see the variables we just

created appear in the boxes below

This is what the Identity window should look like after you have selected

TodoViewController

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Now that the class is associated, we can begin connecting the

components We will start by connecting the view Click on the top of your

view window to select the view itself (make sure you haven‟t selected any

of the UI components) Click Tools -> Connections Inspector Next to

where is says “New Referencing Outlet” click in the circle and drag it to the

“File‟s Owner” object and release it The word “view” should pop up Click

on the word view It should now look like this

Now repeat these steps for each of the components (UITextView,

UISegmentedControl, UILabel, UIButton) connecting each to the “File‟s

Owner Object” Instead of the word “view” popping up, you should see the

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variable name for the corresponding variable that you want to connect the

component to So for the UITextView, you should see the word “todoText”

appear when you drag it to the File‟s Owner object

We need to connect the UIButton to the updateStatus method we created

To do this click inside the “Touch up inside” circle and drag it to the “File‟s

Owner” object You should see the text “updateStatus” appear Click on it

If all goes well it should look like this

The last thing we need to do inside of Interface Builder is connect the

UISegmentedControl Click on it in your view and then click Tools ->

Connections Inspector… Click on the circle next to the “Value Changed”

method and drag it to the “File‟s Owner” object You will see the method

updatePriority popup Go ahead and click on it Your window for the

UISegmentedControl should now look like this:

Collection By traibingo 111 Now, let‟s display this view when a row is selected Close Interface Builder

and open up RootViewController.h and add the following code:

We need a variable to associate with the TodoViewController that we will

be transitioning to Next, open up RootViewController.m and add the

following code to synthesize this property

Keeping the UITableView Up To Date

Whenever a todo item is altered (status or priority) the UITableView needs

to be updated with the new changes Add the following code to the

viewWillAppear

The line [self.tableView reloadData] reloads the table data every time the

view appears (or reappears) This will ensure that our table is always up to

date

Now add the following code to the didSelectRowAtIndex method:

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This is quite a bulky method with a lot of familiar code First, we get a

handle to the appDelegate and the todo object that was selected Next, we

push the todoView (the view you created in interface builder) on to the

viewController stack to transition to it After that, we are setting some of the

properties of the view The title is set to the text of the todo (it will get

truncated if it is too long) and the UITextView is also set to the todo text

Next, we are translating our priority to an index for the UISegmentedView I

explained why this was necessary above Then the index of the

UISegmentedControl is set by using the setSelectedSegmentIndex

method Finally, we set the text of the button and label based on the status

of the todo

The very last thing we need to do is tell the application to save itself when it

closes Open up todoAppDelegate.m and add the following code to the

applicationWillTerminate method:

If you ask me, this is some freakin sweet functionality The method

“makeObjectsPerformSelector” is a built in method on an NSArray It

basically loops over every object in the array, calling the method you pass

in to it on each one It‟s like doing a for loop and calling the

todo[x].dehydrate method for each todo Only this is much cleaner So, to

reiterate, this method will call the dehydrate method on each todo If the

todo is “dirty” meaning it was altered, it will be saved to the database,

otherwise the dehydrate method will do nothing

* One thing to note The applicationWillTerminate method will not be called

if you quit the simulator while the application is running To make sure it

gets called (and the todo data gets saved) make sure you press the home

button on the simulator after you make alterations to the todos If you

simply press Apple-q and quit the simulator while inside of the todo

program, no data will be saved and you will post angry comments on my

site telling me that my tutorial is wrong

Click Build and Go and just sit back and enjoy the magic of rock! I mean

XCode…

When you select a todo item, your screen should look something like this:

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Well, that concludes part 3 of our series Join me next time, when I will

show you how to add and delete todos from the SQLite database If you

have any comments or questions, feel free to leave them in the comments

section I would love to hear them Please subscribe to the RSS feed if you

want to be automatically notified of new tutorials If you get lost at any

point, you can download the sample code for this tutorial here