用 Kotlin 开发 Android 项目的感受

fun demo() {
    val string1: String = "string1"
    val string2: String? = null
    val string3: String? = "string3"
    println(string1.length) //7
    println(string2?.length)  //null
    println(string3?.length)  //7
}

if(view instanceof TextView) {
    TextView textView = (TextView) view;
    textView.setText("text");
}

if(view is TextView) {
    TextView textView = view as TextView
    textView.setText("text")
}

if(view instanceof TextView) {
    ((TextView) view).setText("text");
}

if(view is TextView) {
    (view as TextView).setText("text")
}

if(view is TextView) {
    view.setText("text")
}

val a: A? = A()
if (a != null) {
    println(a?.b)
}

fun testWhen(obj: Any) {
    when(obj) {
        is Int -> {
            println("obj is a int")
            println(obj + 1)
        }
        is String -> {
            println("obj is a string")
            println(obj.length)
        }
        else -> {
            println("obj is something i don‘t care")
        }
    }
}
fun main(args: Array<String>) {
    testWhen(98)
    testWhen("98")
}

fun testWhen(int: Int) {
    when(int) {
        in 10 .. Int.MAX_VALUE -> println("${int} 太大了我懒得算")
        2, 3, 5, 7 -> println("${int} 是质数")
        else -> println("${int} 不是质数")
    }
}
fun main(args: Array<String>) {
    (0..10).forEach { testWhen(it) }
}

0 不是质数
1 不是质数
2 是质数
3 是质数
4 不是质数
5 是质数
6 不是质数
7 是质数
8 不是质数
9 不是质数
10 太大了我懒得算

(0 until container.childCount)
        .map { container.getChildAt(it) }
        .filter { it.visibility == View.GONE }
        .forEach { it.visibility = View.VISIBLE }

for(int i = 0; i < container.childCount - 1;  i++) {
    View childView = container.getChildAt(i);
    if(childView.getVisibility() == View.GONE) {
        childView.setVisibility(View.VISIBLE);
    }
}

async {
    val response = URL("https://www.baidu.com").readText()
    uiThread {
        textView.text = response
    }
}

object Log {
    fun i(string: String) {
        println(string)
    }
}
fun main(args: Array<String>) {
    Log.i("test")
}

class Person(var name: String)
val person = Person("张三");

class Person(var name: String = "张三")
val person = Person()

data class Column(
        var subId: String?,
        var subTitle: String?,
        var subImg: String?,
        var subContentnum: Int?,
)

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.2"
    defaultConfig {
        applicationId "com.zll.demo"
        minSdkVersion 15
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile(‘proguard-android.txt‘), ‘proguard-rules.pro‘
        }
    }
}

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    val homeFragment = HomeFragment()
    val columnFragment = ColumnFragment()
    val mineFragment = MineFragment()
    setContentView(
            tabPages {
                backgroundColor = R.color.white
                dividerColor = R.color.colorPrimary
                behavior = ByeBurgerBottomBehavior(context, null)
                tabFragment {
                    icon = R.drawable.selector_tab_home
                    body = homeFragment
                    onSelect { toast("home selected") }
                }
                tabFragment {
                    icon = R.drawable.selector_tab_search
                    body = columnFragment
                }
                tabImage {
                    imageResource = R.drawable.selector_tab_photo
                    onClick { showSheet() }
                }
                tabFragment {
                    icon = R.drawable.selector_tab_mine
                    body = mineFragment
                }
            }
    )
} 

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    verticalLayout {
        textView {
            text = "这是标题"
        }.lparams {
            width = matchParent
            height = dip(44)
        }
        textView {
            text = "这是内容"
            gravity = Gravity.CENTER
        }.lparams {
            width = matchParent
            height = matchParent
        }
    }
}

class Preference<T>(val context: Context, val name: String?, val default: T) : ReadWriteProperty<Any?, T> {
    val prefs by lazy {
        context.getSharedPreferences("xxxx", Context.MODE_PRIVATE)
    }
    override fun getValue(thisRef: Any?, property: KProperty<*>): T = with(prefs) {
        val res: Any = when (default) {
            is Long -> {
                getLong(name, 0)
            }
            is String -> {
                getString(name, default)
            }
            is Float -> {
                getFloat(name, default)
            }
            is Int -> {
                getInt(name, default)
            }
            is Boolean -> {
                getBoolean(name, default)
            }
            else -> {
                throw IllegalArgumentException("This type can‘t be saved into Preferences")
            }
        }
        res as T
    }
    override fun setValue(thisRef: Any?, property: KProperty<*>, value: T) = with(prefs.edit()) {
        when (value) {
            is Long -> putLong(name, value)
            is String -> putString(name, value)
            is Float -> putFloat(name, value)
            is Int -> putInt(name, value)
            is Boolean -> putBoolean(name, value)
            else -> {
                throw IllegalArgumentException("This type can‘t be saved into Preferences")
            }
        }.apply()
    }
}

class EntranceActivity : BaseActivity() {
    private var userId: String by Preference(this, "userId", "")
    override fun onCreate(savedInstanceState: Bundle?) {
        testUserId()
    }
    fun testUserId() {
        if (userId.isEmpty()) {
            println("userId is empty")
            userId = "default userId"
        } else {
            println("userId is $userId")
        }
    }
}

fun ImageView.displayUrl(url: String?) {
    if (url == null || url.isEmpty()) {
        imageResource = R.mipmap.ic_launcher
    } else {
        Glide.with(context)
                .load(ColumnServer.SERVER_URL + url)
                .into(this)
    }
}
...
val imageView = findViewById(R.id.avatarIv) as ImageView
imageView.displayUrl(url)

val onlyTv = findViewById(R.id.onlyTv) as TextView

val onlyTv = find<TextView>(R.id.onlyTv)
val onlyTv: TextView = find(R.id.onlyTv)

inline fun <reified T : View> Activity.find(id: Int): T = findViewById(id) as T

import kotlinx.android.synthetic.main.activity_main.*
...
onlyTv.text="不需要声明直接可以用"

Intent intent = new Intent(LoginActivity.this, MainActivity.class);
intent.putExtra("name", "张三");
intent.putExtra("age", 27);
startActivity(intent);

startActivity<MainActivity>()
startActivity<MainActivity>("name" to "张三", "age" to 27)
startActivityForResult<MainActivity>(101, "name" to "张三", "age" to 27)

Toast.makeText(context, "this is a toast", Toast.LENGTH_SHORT).show();

context.toast("this is a toast")

toast("this is a toast")

longToast("this is a toast")

class A(val b: B)
class B(val c: C)
class C(val content: String)

C c = new C("content");
B b = new B(c);
A a = new A(b);

@kotlin.internal.InlineOnly
public inline fun <T> T.apply(block: T.() -> Unit): T { block(); return this }

public fun <T> T.apply(block: T.() -> Unit): T {
    block()
    return this
}

val textView = TextView(context).apply {
    text = "这是文本内容"
    textSize = 16f
}

layout.addView(TextView(context).apply {
    text = "这是文本内容"
    textSize = 16f
})

val a = A().apply {
    b = B().apply {
        c = C("content")
    }
}