使用Eclipse开发Android OpenCV应用指南

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"Android Application Programming with OpenCV.pdf" 本书主要涵盖了Android应用开发的多个方面，特别强调了使用Eclipse集成开发环境（IDE）进行Android应用程序的构建。书中详细介绍了如何利用OpenCV库在Android平台上开发图像处理和计算机视觉相关的应用程序。在Android Primer章节，作者Onur Cinar介绍了Android操作系统的基本概念，包括它的架构、组件模型以及应用程序生命周期。这部分内容对初学者尤其重要，因为理解这些基础知识是开发任何Android应用的基础。 Chapter 2：Application Architecture深入讨论了Android应用的架构，包括Activity、Service、Broadcast Receiver、Content Provider等核心组件。开发者会了解到如何设计和组织应用程序的不同部分以实现高效和灵活的交互。 Chapter 3和4：Eclipse Primer及Mastering Eclipse，这两章专注于Eclipse IDE的使用，包括安装配置、项目管理、调试技巧以及使用插件提升开发效率。这对于任何使用Eclipse的开发者来说都是必不可少的知识，它将帮助你更有效地进行代码编写和测试。 Chapter 5：Android Development Tools for Eclipse进一步探讨了专为Android开发定制的工具集ADT（Android Development Tools），包括使用ADT创建项目、布局编辑器和图形化界面设计等。在后面的部分，作者通过实际项目如MoviePlayer来引导读者实践。Chapter 6至Chapter 10分别涉及使用Eclipse进行原生开发、扩展MoviePlayer支持AVI电影、使用脚本语言进行Android开发以及结合HTML和JavaScript创建电影播放器。这些章节提供了丰富的实践案例，帮助读者巩固理论知识并提高实际编程技能。在Appendix A：Testing Android Applications中，读者可以学习到如何对Android应用进行测试，包括单元测试、集成测试和性能测试，以确保应用的质量和稳定性。这本书是Android开发者，特别是那些想要结合OpenCV进行图像处理开发者的宝贵资源。它不仅提供了一个从基础到高级的完整教程，还通过实际项目让读者有机会将所学知识付诸实践。通过阅读本书，开发者不仅可以掌握Android应用开发的基本技能，还能了解到如何在Eclipse环境下高效地使用OpenCV库，从而拓宽在移动平台上的应用开发能力。

CHAPTER 1: Android Primer

Figure 1-3. Binder kernel module allowing two applications to communicate

Binder’s user-space code maintains a pool of threads in each process, and

these threads are used to process incoming Binder requests as local events.

Binder is also responsible for tracking the object references across processes.

Additionally, Binder provides an extra level of security, by transmitting the user

and group ID of the calling process with each Binder request.

Binder is a key construct in the Android platform. It is the central messaging

channel across the entire Android platform. Android applications communicate

with the system, services, and each other through the Binder interface.

Although Binder is implemented as a low-level service, application developers

are not expected to directly interact with it. The Android runtime provides the

android.os.IBinder interface as the API to communicate with other processes

through Binder. Android provides the Android Interface Definition Language

(AIDL), which is tuned for Binder.

AIDL allows you to define the programming interface that the client and server

will use to communicate with each other. As with many other operating systems,

on Android, the processes are not allowed to access the memory of another

process directly. AIDL provides the functionality to decompose the objects into

primitives that Binder can understand and use across project boundaries.

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CHAPTER 1: Android Primer

Threading is one of the most important parts of interacting with Binder:

 Calls made from the local process are executed in the calling

thread. Binder calls are synchronous and will block the current

thread until the request is processed. If the request is

expected to take a long time to complete, the request should

not be made from the application’s main thread. This would

make the application hang, and may result in the application

being terminated by the Android platform. Binder also

supports nonblocking requests through the oneway attribute.

 Calls from a remote process are dispatched from the thread

pool provided by the local process. The service code is

expected to be thread-safe, since the requests can be

executed by any of these threads.

Android SDK provides the necessary code generators to translate programming

interfaces that are defined in AIDL into actual Java classes. Application

developers are only expected to provide the implementation for the generated

interface and the Android service that will provide the interface to the clients.

Wakelocks

Android is designed to operate on mobile platforms with scarce resources.

Because of this, Android devices go into sleep mode very frequently. Although

this allows the system to use the available resources efficiently, it is not

preferable for the device to go into sleep mode while the kernel or an application

is in the middle of an important process. Wakelocks were introduced as a kernel

patch in order to allow an application to prevent the system from going into

sleep mode while it is performing a task.

Two types of wakelocks are supported by the Android platform:

 An idle wakelock prevents the system from entering a low-

power idle state.

 A suspend wakelock prevents the system from entering a full-

system suspend state.

Application developers interact with wakelocks through the

android.os.PowerManager.WakeLock interface. To use this interface, the

application should request android.permission.WAKE_LOCK in advance.

Wakelocks should be used with caution. Preventing the device from going into

sleep mode will increase the power consumption, which will eventually cause it

to run out of battery power. An application should hold the wakelock during

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CHAPTER 1: Android Primer

simplify this procedure, the Android logging system groups the log messages

into four separate log buffers:



Main:

Main application log messages



Events:

System events



Radio:

Radio-related log messages



System:

Low-level system debug messages for debugging

These four buffers are kept as pseudo-devices under the /dev/log system

directory. Since input and output (I/O) operations on mobile platforms are very

costly, the log messages are not saved in persistent storage; instead, they are

kept in memory. In order to keep the memory utilization of the log messages

under control, the logger module puts them in fixed-sized buffers. Main, radio,

and system logs are kept as free-form text messages in 64KB log buffers. The

event log messages carry additional information in binary format, and they are

kept in a 256KB log buffer.

A set of user-level applications is also provided to view and filter these logs,

such as the logcat and the Dalvik Debug Monitor Server

(DDMS) tools, which we

will examine in chapter 5.

The Android runtime provides a set of API calls to allow applications to easily

send their log messages to the logger. Application log messages are sent

through the following classes:

 android.util.Log: This class is used to send application log

messages. It provides a set of methods to specify the priority

of the message, as well as a tag to indicate which application

is generating this log message.

 android.util.EventLog: This class is used to send event log

messages in binary format.

 android.util.Slog: This class is used by the Android runtime

components to send system log messages. It is not part of the

Android API, and it is not accessible from the applications.

Zygote

On most UNIX-like operating systems, the application that is known as Init is

considered as the parent of all processes. Init gets started after the kernel

successfully boots. Its primary role is to start a set of other processes based on

the system configuration.

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