Kotlin学习笔记（六十二）Kotlin Android

以下是一个Kotlin版Android程序的小例子

先在build.gradle文件中添加布局拓展，可以在java文件中直接使用在布局文件中声明的id的控件，省去findViewById的步骤。

apply plugin: 'kotlin-android-extensions'

再在build.gradle中的dependencies中添加anko，可以直接在java文件中写布局，省去xml文件。

compile "org.jetbrains.anko:anko-sdk15:0.9.1"

activity_main.xml

MainActivity.java

package linchange.example.com.kotlin_android2

import android.os.Bundle
import android.support.design.widget.Snackbar
import android.support.v7.app.AppCompatActivity
import android.view.Menu
import android.view.MenuItem
import kotlinx.android.synthetic.main.activity_main.*
import kotlinx.android.synthetic.main.content_main.*
import org.jetbrains.anko.onClick
import org.jetbrains.anko.startActivity

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        setSupportActionBar(toolbar)

        fab.onClick { view -> //为浮动按钮设置点击事件
            Snackbar.make(view!!, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show()
            tv.text = "${System.currentTimeMillis()}" //设置textView的文本内容为当前时间

            //跳转页面，泛型为需要跳转的页面，圆括号中的键值对为所需放入的Extras
            startActivity("Key" to "from The Great Wall")
        }
    }

    override fun onCreateOptionsMenu(menu: Menu): Boolean {
        menuInflater.inflate(R.menu.menu_main, menu)
        return true
    }

    override fun onOptionsItemSelected(item: MenuItem): Boolean {
        val id = item.itemId

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

        return super.onOptionsItemSelected(item)
    }
}

Main2Activity.java

package linchange.example.com.kotlin_android2

import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import android.text.Editable
import android.text.TextWatcher
import android.view.Gravity
import android.widget.Toast
import org.jetbrains.anko.relativeLayout
import org.jetbrains.anko.textView
import org.jetbrains.anko.wrapContent

class Main2Activity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        relativeLayout { //相对布局
            textView(intent.extras["Key"]?.toString() ?: "Nothing") { //设置textView的文字
                addTextChangedListener(object : TextWatcher { //匿名对象调用接口
                    override fun afterTextChanged(s: Editable?) {
                        Toast.makeText(this@Main2Activity, "textView Change", 
                            Toast.LENGTH_SHORT).show()
                    }

                    override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {
                    }

                    override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {
                    }
                })
            }.lparams(wrapContent, wrapContent) { //设置textView的布局参数
                gravity = Gravity.CENTER
            }
        }

    }
}

MainActivity视图

Main2Activity视图