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Just as humans utilize memory for holding information, apps also rely on memory slots for data management. In this chapter, you'll explore how to establish an app's memory, manage storage in named memory slots, and retrieve information effectively. By understanding properties and variables, you’ll learn how to define, set, and manipulate these components to enhance your app's functionality. This knowledge will also empower you to create a more efficient user interface while separating computation from presentation in your applications.
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Memory Slots • Just as people need to remember things, so do apps. • When someone tells you the phone number of a pizza place for a onetime immediate call, your brain stores it in a memory slot. • In this chapter, you’ll learn how to set up an app’s memory, how to store information in it, and how to retrieve that information at a later time.
Named Memory Slots • An app’s memory consists of a set of named memory slots. • Some of these memory slots are created when you drag a component into your app; these slots are called properties. • You can also define named memory slots that are not associated with a particular component; these are called variables.
1. Properties • Components (Button, TextBox, and Canvas…) • are part of the user interface. • Each component is completely defined by a set of properties. • The values stored in the memory slots of each property determine how the component appears.
Modifying the memory slots in the property form to change the app’s appearance
2. Variables • Defining Variables • Setting and getting a Variable • Setting a Variable to an Expression • Incrementing a Variable • Building Complex Expressions • Displaying Variables
2.1 Defining Variables • You define a variable when your app needs to remember something that is not being stored within a component property. • For example, a game app might need to remember what level the user has reached. • If the level number is not something the user will see, you’d define a variable to store it.
Defining Variables 1. 拖曳出 initialize global name to
Defining Variables 2. 設定變數名稱 3. 設定初值
2.2 Setting and getting a Variable • 設定(變更)變數值 選擇變數名稱
Setting and getting a Variable • 取得變數值 選擇變數名稱
2.3 Setting a Variable to an Expression • Incrementing a Variable • Building Complex Expressions
Math drawer • In the Math drawer, App Inventor provides a wide range of mathematical functions.
2.4 Displaying Variables • Changing a variable has no direct effect on the app’s appearance. • When you modify a component property, the user interface is directly affected. This is not true for variables. • This is one of the advantages of storing data in a variable as opposed to a component property • it allows you to show just the data you want when you want to show it. • It also allows you to separate the computational part of your app from the user interface, making it easier to change that user interface later.
1. 複製專案進行修改 • 開啟HelloPurr專案，Save as為HelloPurr_Extend
Media部分，以Upload File加入獅子圖片(lion.jpg)與獅吼聲音(roar.mp3)
回顧：Button1的Image屬性，決定該按鈕的長相(顯示哪張圖片)回顧：Button1的Image屬性，決定該按鈕的長相(顯示哪張圖片)
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