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Programming Your App’s Memory

靜宜大學資管系 楊子青

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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.

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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.

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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 prop

erty determine how the component appears.

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Modifying the memory slots in the property form to change the app’s appearance

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2. Variables

• Defining Variables

• Setting and getting a Variable

• Setting a Variable to an Expression– Incrementing a Variable

– Building Complex Expressions

• Displaying Variables

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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.

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Defining Variables

1. 拖曳出 initialize global name to

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Defining Variables

2. 設定變數名稱

3. 設定初值

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2.2 Setting and getting a Variable

• 設定 ( 變更 ) 變數值

選擇變數名稱

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Setting and getting a Variable

• 取得變數值

選擇變數名稱

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2.3 Setting a Variable to an Expression

• Incrementing a Variable

• Building Complex Expressions

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Math drawer

• In the Math drawer, App Inventor provides a wide range of mathematical functions.

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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.

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HelloPurr_Extend

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1. 複製專案進行修改• 開啟 HelloPurr 專案， Save as 為 HelloPurr_Extend

靜宜大學資管系 楊子青 17Media 部分，以 Upload File 加入獅子圖片 (lion.jpg) 與獅吼聲音 (roar.m

p3)

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回顧： LabelName 的 Text 屬性，決定顯示文字內容

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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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回顧： Sound1 的 Source 屬性，決定播放哪個聲音檔

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如何動態調整顯示文字？圖片？聲音？

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執行結果：初次播放 roar.mp3 發生 error

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Google 找解決方法

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Screen1.Initialize

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鱷魚拔牙整人玩具http://www.i-gamer.net/play/2978.html

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2. 按圖片，第 6 次出現獅子

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3. 隨機第 2-6 次出現獅子