iPhone Programming Tutorial – Creating a ToDo List Using SQLite Part 4

    September 22nd, 2008 Posted by: - posted under:Tutorials

    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:

    When you have completed this tutorial, you should have a main screen that looks something like this:

    Let’s get started…

    The first thing we need to do is add the UIBarButtonItem items to the NavigationBar so that we get the “Edit” and “Add” button. Open up 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:

    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 declared in a previous step. First, we check to see if it is nil. If it is we compile the statement using the sqlite3_prepare statement. Next, we bind the primary key of the current todo to the “?” in the sqlite3 statement. Next, 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.

    Happy iCoding!