Like radio buttons, a pop-up button lets the user select only from a predefined list of options. Unlike radio buttons, a pop-up button always takes up a fixed amount of space no matter how many options you want to display to the user.

A pop-up button displays the currently selected option as a wide but short button. As soon as the user clicks the button, the pop-up menu expands to show a list of options, as shown in Figure 17-1. From this expanded list, the user can click one of the many available options.

Figure 17-1. A pop-up button takes up minimal amount of space, but can provide a list of choices when clicked.

To create a pop-up button, just open the Library window in Interface Builder by choosing Tools

Figure 17-2. The Pop Up Button object appears in the Object Library.

After you've placed a Pop Up Button object on your user interface window, the next step is to fill its list with different choices. There are two ways to create and edit a pop-up button list:

Using Interface Builder is simple since you just need to type or edit a list of options. However, once your program starts running, your pop-up button list remains fixed. Using Objective-C code to create a pop-up button list is much harder, but it gives you the flexibility of changing the list as your program runs.

You can use either method separately or both in combination. For example, you might create your initial pop-up button list in Interface Builder, and then modify it using Objective-C code as your program runs. Let's see how to do so now.

By default, every pop-up button comes with three items, labeled Item 1, Item 2, and Item 3. To create your own list of choices, you have to rename these existing default choices and add or delete additional items, depending on how many choices you want to offer. To create a pop-up button and edit its existing three items, follow these steps:

Renaming an Item in a Pop-Up Button List

After adding or deleting items in a pop-up button's list, you need to rename the items so they don't display a generic title like Item 2 or Item 3. There are two ways to rename an item, as shown in Figure 17-7:

Figure 17-7. The two ways to rename an item displayed in a pop-up button's list

• Double-click the pop-up button directly on your user interface to display its list of choices. Then double-click the item that you want to rename and type new text.

• Double-click the pop-up button directly on your user interface to display its list of choices. Then click the item in the list that you want to rename. Choose Tools

  

Another way to modify a pop-up button's list of choices is to create an array and then load that array of data into the pop-up button's list. This option requires writing Objective-C code and connecting your code to the pop-up button on your user interface.

To connect your Objective-C code to a user interface object, you must create something called an IBOutlet. Basically, any variable declared as an IBOutlet can display data to a user interface object, such as a pop-up button.

Next, you need to create an array and fill it with data. Then you need to store this array of data in your IBOutlet variable that's connected to your pop-up button, which will display your data on the screen.

To see how to create an array and connect this data to a pop-up menu button, follow these steps:

If you define your pop-up button's list of choices through Interface Builder, you can identify each choice by the title or tag property. If you create your pop-up button's list of choices with an array using Objective-C code, you can identify what the user selected through the text of that item or the index position of the selected item.

The Title property identifies the actual text of the option that the user clicked. The Tag property identifies an arbitrary numeric value assigned to each option through the Object Attributes window. With either property, you must make sure that all your pop-up button's options have different Title or Tag values.

The problem with identifying menu items through the Title value is that you must identify the text exactly. If the menu item is "Open File" and your Objective-C code searches for "open file" instead, the code won't work since the text isn't exactly the same. For that reason, you may prefer to identify a selected menu item by using its index position.

The first (top) menu item is considered at index position 0, the second at index position 1, and so on. By searching for index position, you don't have to worry about the actual text displayed by each menu item.

To retrieve the index position of an item in a menu, you need to retrieve the value of the index item, stored in the indexOfSelectedItem property. After you retrieve this index value, you need to store it in a variable such as:

-(IBAction)findSelectedButton:(id)sender;
    {
         NSInteger index = [sender indexOfSelectedItem];
         NSLog(@"Selected item index is %i", index);
    }

If the preceding method were connected to a pop-up button, the sender would retrieve the item that the user selected in the pop-up button, and the indexOfSelectedItem property would retrieve that selected item's index position.

To see how to identify a selected item chosen from a pop-up button by its displayed text (Title property) or its index position, follow these steps:

Notice that the Tag property of both items is 0 because you didn't define this value. If you created your pop-up button's list of options through Interface Builder, you could set this Tag property of each item through the Object Attributes window.

Think of pop-up buttons as an alternative to radio buttons. Whenever your number of options starts to get too numerous to display as multiple radio buttons, switch to a pop-up button that can take up a minimal amount of space and still display a huge list of options for the user to select. The only drawback is that, whereas radio buttons make the options clearly visible at all times, a pop-up button requires that the user click it to see the list of choices.

The simplest and most straightforward way to create a list of options to display on a pop-up button is to expand the icon view that appears between the left and middle pane of the Xcode window. Then you can add, delete, or rename items that you want to appear as choices in your pop-up button list.

If you just want to rename the list of items in the pop-up button, you can either double-click the pop-up button directly to view and edit its list of choices, or you can double-click the pop-up button directly, click each item in the list, and open its Object Attributes window to edit the Title text and add a distinct value to each item's Tag property.

If you need to change the list of items displayed in a pop-up button, you can create its list of choices using Objective-C code. First, you need to create an IBOutlet variable to connect with your pop-up menu. Then, you need to connect your pop-up button on the user interface to the IBOutlet variable. Finally, you need to create an array of your pop-up button options, and then store this array in the IBOutlet variable that represents your pop-up button. Linking this IBOutlet variable to your pop-up button on the user interface allows the array data to appear as the pop-up button's list of choices.

Whenever you need to display a large number of choices in a small amount of space, use a pop-up button. By filling a pop-up button's list using an array and Objective-C code, you can even change the pop-up button's list of choices while your program runs.