Android应用开发入门：实战指南

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"Android Recipes 2nd Edition" 本书《Android Recipes 2nd Edition》是一本针对Android应用开发者的实用指南，旨在帮助那些想要进入Android开发领域的初学者快速上手。作者Dave Smith和Jeff Friesen提供了一种问题-解决方案的方法，通过理论介绍和具体实例，让读者能够掌握开发和发布Android应用的基础知识。在Android开发领域，Google提供了详尽的在线Android开发者指南，但这个指南内容庞杂，可能对新手来说有些难以消化。本书则以简洁明了的方式，讲解了Android开发的基本概念，并通过一系列的“食谱”（recipes）来教授实际的开发技巧。这些食谱涵盖了从创建用户界面到与设备硬件和媒体交互，再到数据持久化、系统交互、库的使用、Android NDK和RenderScript的运用等多个方面。书中详细内容包括： 1. 第1章：Getting Started with Android，介绍了Android开发环境的搭建、基本的开发工具以及如何建立第一个Android项目。 2. 第2章：User Interface Recipes，讲解了Android UI设计的各种组件和布局，以及如何创建响应式和吸引人的用户界面。 3. 第3章：Communications and Networking，探讨了应用程序如何进行网络通信，如HTTP请求、数据传输和WebSocket等。 4. 第4章：Interacting with Device Hardware and Media，涵盖了与设备硬件（如相机、传感器）和多媒体文件（音频、视频）的交互。 5. 第5章：Persisting Data，讨论了数据存储的各种方法，包括SQLite数据库、SharedPreferences、文件存储等。 6. 第6章：Interacting with the System，讲述了如何使用Android系统服务、权限管理和广播接收器。 7. 第7章：Working with Libraries，介绍了如何集成和使用第三方库，以增强应用程序的功能。 8. 第8章：Working with Android NDK and Renderscript，讲解了原生开发工具包(NDK)和渲染脚本(Renderscript)的应用，用于提高性能和处理特定计算任务。 9. 附录部分提供了关于Scripting Layer for Android、Android Tools的概述，以及App Design Guidelines和Univerter Architecture的相关信息。这本书不仅适合初学者，也对有经验的开发者具有参考价值，因为它提供了大量可直接应用于实际项目的代码示例和最佳实践。通过阅读和实践书中的“食谱”，读者可以逐步建立起自己的Android开发技能，最终能够成功地将应用程序发布到Google Play商店。

CHAPTER 1: Getting Started with Android

Figure 1-2. The main activity of Android’s Calculator app lets the user perform basic calculations.

Although an app can include a single activity, it’s more typical for apps to

include multiple activities. For example, the Calculator app also includes an

‘‘advanced panel’’ activity that lets the user calculate square roots, perform

trigonometry, and carry out other advanced mathematical operations.

Activities are described by subclasses of the android.app.Activity class, which

is an indirect subclass of the android.content.Context class.

NOTE: Context is an abstract class whose methods let apps access global

information about their environments (such as their resources and filesystems), and

let apps perform contextual operations, such as launching activities and services,

broadcasting intents, and opening private files.

Activity subclasses override various Activity

life cycle callback methods

that

Android calls during the life of an activity. For example, the SimpleActivity

class in Listing 1-1 extends Activity and also overrides the void

onCreate(Bundle bundle) and void onDestroy() life cycle callback methods.

Listing 1-1. A Skeletal Activity

import android.app.Activity;

import android.os.Bundle;

public class SimpleActivity extends Activity

{

@Override

public void onCreate(Bundle savedInstanceState)

{

super.onCreate(savedInstanceState); // Always call superclass method

first.

System.out.println("onCreate(Bundle) called");

}

@Override

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CHAPTER 1: Getting Started with Android

specified int result is returned to Activity’s void onActivityResult(int

requestCode, int resultCode, Intent data) callback method as an argument.

NOTE: The responding activity can look at the intent that caused it to be launched by

calling Activity’s Intent getIntent() method. Android calls the activity’s

void onNewIntent(Intent intent) method (also located in the Activity

class) to pass any subsequent intents to the activity.

Suppose that you’ve created an app named SimpleActivity, and that this app

consists of SimpleActivity (described in Listing 1-1) and SimpleActivity2

classes. Now suppose that you want to launch SimpleActivity2 from

SimpleActivity’s onCreate(Bundle) method. The following example shows you

how to start SimpleActivity2:

Intent intent = new Intent(SimpleActivity.this, SimpleActivity2.class);

SimpleActivity.this.startActivity(intent);

The first line creates an Intent object that describes an explicit intent. It

initializes this object by passing the current SimpleActivity instance’s reference

and SimpleActivity2’s Class instance to the Intent(Context packageContext,

Class<?> cls) constructor.

The second line passes this Intent object to startActivity(Intent), which is

responsible for launching the activity described by SimpleActivity2.class. If

startActivity(Intent) was unable to find the specified activity (which shouldn’t

happen), it would throw an android.content.ActivityNotFoundException

instance.

Figure 1-3 also reveals that onDestroy() might not be called before the app is

terminated. As a result, you should not count on using this method as a place

for saving data. For example, if an activity is editing a content provider’s data,

those edits should typically be committed in onPause().

NOTE: onDestroy() is usually implemented to free system resources (such as

threads) that were acquired in onCreate(Bundle).

The seven life cycle callback methods define an activity’s entire life cycle and

describe the following three nested loops:

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