如何创建一个Kotlin项目

前言：Google I/O 2017正式将Kotlin语言作为Android开发最新的 First-class编程语言，而且Android Studio 3.0 已加入对其的支持。

安装插件

这点先暂时这么干着，升级到3.0后就不用了，至于这么安装Kotlin插件，自己Google吧，不是重点。

配置Gradle

项目下的build.gradle要添加：

buildscript {
    ext.support_version = '25.3.1' //支持库版本
    ext.kotlin_version = '1.1.2-3'  //kotlin版本
    ext.anko_version = '0.8.2'  //anko库版本

    repositories {
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:2.3.0'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        jcenter()
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

app下的build.gradle要添加：

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'

android {
    compileSdkVersion 25
    buildToolsVersion "25.0.2"
    defaultConfig {
        applicationId "com.example.fleming.myapplication"
        minSdkVersion 15
        targetSdkVersion 25
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    compile "com.android.support:appcompat-v7:$support_version"
    compile 'com.android.support.constraint:constraint-layout:1.0.2'
    compile "com.android.support:design:$support_version"
    testCompile 'junit:junit:4.12'

    // kotlin
    compile "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
    compile "org.jetbrains.anko:anko-common:$anko_version"
}

buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath "org.jetbrains.kotlin:kotlin-android-extensions:$kotlin_version"
    }
}

完成后点击Sync Now同步一下。

将Java文件转换成Kotlin文件

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val toolbar = findViewById(R.id.toolbar) as Toolbar
        setSupportActionBar(toolbar)

        val fab = findViewById(R.id.fab) as FloatingActionButton
        fab.setOnClickListener { view ->
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show()
        }
    }

    override fun onCreateOptionsMenu(menu: Menu): Boolean {
        // Inflate the menu; this adds items to the action bar if it is present.
        menuInflater.inflate(R.menu.menu_main, menu)
        return true
    }

    override fun onOptionsItemSelected(item: MenuItem): Boolean {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        val id = item.itemId


        if (id == R.id.action_settings) {
            return true
        }

        return super.onOptionsItemSelected(item)
    }
}

当然也可以单击右键选择New —> Kotlin Activity

最后

其实在github已经有很多开发者使用kotlin编写出了不错的项目，如何快速学习并掌握这门语言呢？点击这里 大家一起学吧！