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Programming Your App’s Memory 靜宜大學資管系 楊子青. 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.
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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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