Android basic concepts

Android System Architecture

Linux kernel Linux kernel layer is a layer of various hardware devices Android provide the underlying drive.
The system runtime layer provides the main characteristics of the support, as well as the core Java libraries for Androin system through a number of C / C ++ libraries
Application Framework API layer provides a variety of building applications when
Various applications installed application layer

Four components

Activities (Activity) Android applications, the visible parts are on the move
Service (Service) running in the background, even if the application is still running exit
Broadcast receiver (the BroadcastReceiver) receiving a broadcast message from the broadcast message around and send out
A receiver to share information between the content (the ContentProvider) applications

Android Studio project directory Comments

.gradle automatically generated files without manually editing

.idea automatically generated files without manually editing

app project and detailed code resources

build automatically generated when compiling files

gradle gradle wrapper configuration file

.gitignore version control

build.gradle Global gradle build script

gradle.properties global gradle profile

gradlew / gradlew.bat gradle command executed in the command line interface

xxxxx.iml automatically generated a file without modification

local.properties Android SDK specified path in this machine

settings.gradle all modules in a given project introduced

In addition to the app directory, most files and directories are automatically generated, without modification, app contains all the source files.

build automatically generated when compiling files,

Libs project to use third-party jar package

androidTes used to write Android Test Test Case

java place to put all of our Java code

res used in the project to all the pictures, layout, strings and other resources

AndroidManifest.xml whole Android project profile

test test case for writing Unit Test

.gitignore the specified directory or file within the app exclude version control module

app.iml project is automatically generated file

This is the app build.gradle modules build scripts gradle

Confusing rules proguard-rules.pro designated project code

For resources res folder, referred to by the two methods

// define string a program name, located in res / values / strings.xml file
<resources>
    <string name="app_name">HelloWorld</string>
</resources>
By code
    R.string.app_name
XML by
    @string/app_name

Detailed file build.gradle

Android Studio is the use Gradle to build the project. There are two build.gradle project file, a directory is in the outermost layer, one in the app directory. These two documents to build Android Studio projects have played a vital role

// outer layer build.gradle file 
buildscript {
    repositories {
        google()
        JCenter ()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.5.0'
    }
}
 
allprojects {
    repositories {
        google()
        JCenter ()
    }
}
 
task clean(type: Delete) {
    delete rootProject.buildDir
}

Closure of two repositories are declared jcenter () line configuration, it is a code hosting repository, it will choose the Android Open Source Project code hosted on jcenter, dependencies closure using a Gradle plugin classpath declared, finally part of the face is the version number of the plug-in. build.gradle files in the directory outermost layer of analysis is over, you do not need to modify the contents of this file normally, unless you need to add some global project build with.

// inner build.gradle file 
apply plugin: 'com.android.application'
 
android {
    compileSdkVersion 29 // specify the project compiled version 
    buildToolsVersion "29.0.2" // specify the project build 
    defaultConfig {
         applicationId "com.example.testapplication" // Specify project package name 
         minSdkVersion 15 // minimum compatible version 
        targetSdkVersion 29 // has been done in the detailed test version 
        versionCode 1 // specified item version 
        versionName "1.0" // specified item version name 
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }
    {buildTypes // specified installation file generated configuration 
        release {
            minifyEnabled false // whether or not to code obfuscation
            proguardFiles getDefaultProguardFile('proguard-android-optimize.
            txt '),' proguard-rules.pro rule file when the 'confusion //
        }
    }
}
 
{Dependencies // dependencies specified item
     // declare a local jar at all dependent libs added to the project 
    Implementation FileTree (the dir: 'libs', the include: [' * .jar ' ])
     // declare the remote dependencies 
    implementation' androidx .appcompat: AppCompat: 1.0.2 ' 
    Implementation ' androidx.constraintlayout: constraintlayout: 1.1.3 '
     // declare test library 
    testImplementation' JUnit: JUnit: 4.12 ' 
    androidTestImplementation ' androidx.test: Runner: 1.2.0 ' 
    androidTestImplementation ' androidx. test.espresso: Espresso-Core: 3.2.0 ' 
}

Log logging tool

Android logging tools is the Log (android.util.Log).

Log.v (). For printing those most trivial, meaning a minimum of log information. verbose
Log.d (). For printing some debugging information, debug
Log.i (). For printing some of the more important data, info
Log.w (). For printing warning messages, warn
Log.e (). For error Print program, error

//举例
@Override
protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
    switch (requestCode){
        case 1 :
            if(resultCode == RESULT_OK){
                String returnData = data.getStringExtra("data_return");
                Log.d("MainActivity",returnData);
            }
            break;
            default:
    }
}

Note: not recommended for use System.out.println () method! The method of printing log can not control, when the printing

Inter can not be determined, you can not add filters, logs are no tiers.

Android basic concepts

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