android-Brief Introduction

1.android frame Diagram

SGL: 2D graphics engine for embedded device terminals

Webkit: providing a browser engine

FreeType: Drawing of bitmaps and vector fonts.

Dalvik Virtual machine: Unlike a Java Virtual machine, it is optimized to convert a class file into a. dex file format with a "DX" tool,

The Dex file format is more compact and performs more efficiently. Each Android application runs on a separate virtual machine instance. Non-impact,

And it can efficiently generate multiple instances of virtual machines.

2.Android NDK

Android native Development Kit short for Android NDK, allows you to use the components written in C + + on Android applications.

Benefits:

• The code written in Java is easy to decompile, and the anti-compilation of C + + is difficult, so the protection code can be achieved.
• It is easier to reuse third-party code libraries, because most third-party code libraries are written in C + +
• Higher execution speed.
• Portable and easy to run on other embedded devices, such as using OpenGL ES to run on both Android and iOS devices.
• Using the NDK approach: 1. Use the Nativeactivity class provided by the SDK. 2, accessed using JNI.

3.Android Application Basics

When the application runs, a Linux process is started and a Linux user IDis assigned to the application

Only visible within the program, other programs are inaccessible, but you can expose data to other applications through content provider

Use the program.

An application, a process, and a virtual machine instance.

Zygote is a virtual machine process and also an incubator for virtual machine instances. Whenever the system is going to perform a

Application, Zygote will fork out a child process to execute the application. The zygote process is when the system starts

has been initialized, it can quickly improve a new virtual machine instance by replicating itself. For read-only system libraries,

All virtual machine instances and Zygote share the same block memory area. Save on memory overhead.

Structure of the 4.APK file

The application apk file is a file that can be compatible with the ZIP file format. The SDK provides the AAPT tool, which allows the class file

And the resource files are packaged as apk files. Packaging process: Converting Class files to Dex files , generating resource tables , optimizing XML Files

Use the appt Command mode:

1. Add the SDK folder/platform-tools path to the PATH environment first.

2. Enter the bin directory of the Androidproject: enter "appt list <android application name >.apk" to

You can also right-click Androidproject, select Export under Android Tools ... The apk file can be generated.

In a Java file: a reference to a resource, R.resources_type.resources_name or Android. R.resources_type.resources_name (the resource that comes with the system).

In the XML file: Reference method, @resources_type. Resources_name or @android:resources_type.resources_name

5.Intent use

Action: the action performed. such as Intent.action_view,android.content.intent.action_call

Data: The operation is usually a URI type, such as Uri Uri=uri.parse ("smsto:10086");

Type: Specifies the MIME type of data, default is "Text/plain"

Component: Which component (activity or broadcast) handles the intent.

Extras: Additional information, usually in bundle form.

  //the role of intent://1. Invoking the browserUri uri1=uri.parse ("http://www.baidu.com");//DataIntent intent1=NewIntent ();    Intent1.setaction (Intent.action_view);    Intent1.setdata (URI1); //2. Phone Call functionUri uri2=uri.parse ("tel:10086"); Intent Intent2=NewIntent (ANDROID.CONTENT.INTENT.ACTION_CALL,URI2); //3. Send SMSUri uri3=uri.parse ("smsto:10086"); Intent Intent3=NewIntent (INTENT.ACTION_SENDTO,URI3); Intent3.putextra ("Sms_body", "Welcome to Android World"); //4. Send email, you may have more than one mail client, so use//Intent.createchooser () Create a action_chooser intent//1. The recipient's address, the action to send the messageUri uri4=uri.parse ("Mailto:[email protected]"); Intent Intent4=NewIntent (INTENT.ACTION_SEND,URI4); //2. Own mail client, and send the contentIntent4.putextra (Intent.extra_email, "[EMAIL protected]"); Intent4.putextra (Intent.extra_text,"Android Mail"); //3. Specify the type of data, default valueIntent4.settype ("Text/plain"); //Createchooser Start IntentStartActivity (Intent.createchooser (intent4, "Select Email client"));

android-Brief Introduction