br/>
1. kotlin的 apply使用：
有如下Kotlin代码1
2var intent = getInitIntent(readableMap)
intent.setClassName(currentActivity, readableMap.getString("entry"))
在kotlin中又更好实现方式：1
2
3
4
5
6
7 var intent = getInitIntent(readableMap).apply {
setClassName(currentActivity, readableMap.getString("entry"))
}
```
虽然从代码量看都是2行。但后者是将定义及赋值统一为一条语句来实现。
### 2. java中判断字符串值是否相等使用的是equals, 而在kotlin中进行了简化。使用 == 即可。
if ("action".equals(key)) {//java写法,kotlin中不推荐
intent.setAction(readableMap.getString(key))
}
//kotlin中判断两个字符串是否相等跟比较int等number类型一样简单方便
if ("action" == key) {
intent.action = readableMap.getString(key)
}
1 | ### 3. kotlin文件IO提供了很多有用方法。比如要迭代删除文件及子目录下文件夹及文件： |
var file = File(BaseApplication.getInstance().filesDir, "rn")
file.deleteRecursively()
1 |
|
private fun initUpgrade() {
versionRepo = VersionRepo(versionViewModel)
lifecycle.addObserver(versionRepo!!)
}1
所有要使用 versionRepo 变量地方都要加上讨厌的 ? 或者 !! 这就是 lateinit 关键字使用好处之一了：
private lateinit var versionRepo: VersionRepo
初始化后再使用 versionRepo变量都不用再加 ?或者 !!1
2
3### 5. 函数只有一条返回语句的简写
getName方法原来是这么写的
class RnIntentModule(reactContext : ReactApplicationContext?) : ReactContextBaseJavaModule(reactContext) {
override fun getName(): String {
return "RnIntent"
}
}1
现在可以一行简写：
class RnIntentModule(reactContext : ReactApplicationContext?) : ReactContextBaseJavaModule(reactContext) {
override fun getName() = "RnIntent"
}1
2
3
4
### 6. 函数参数带默认值
NotificationUtils.kt
fun buildPushNotification(context: Context, notification: com.govnet.im.main.notification.Notification, intent: Intent): Notification {
return buildPushNotification(context, notification.getNotificationMessage(context), intent)
}
public fun buildPushNotification(context: Context, msg: String, intent: Intent, vibrate: Boolean = false): Notification {
val pendingIntent = PendingIntent.getActivity(context, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT)
val builder = NotificationCompat.Builder(context, SILENT_NOTIFICATION_CHANNEL_ID)
.setWhen(System.currentTimeMillis())
.setContentTitle(defaultTitle)
.setContentText(msg)
.setSmallIcon(defaultIcon)
.setContentIntent(pendingIntent)
.setAutoCancel(true)
.setPriority(NotificationCompat.PRIORITY_DEFAULT)
if (vibrate) {
builder.setVibrate(longArrayOf(0, 1000, 0, 0))
}
return builder.build()
}
1 |
|
public class DateTimePickDialog {
private Activity activity;
public DateTimePickDialog(Activity activity) {
this.activity = activity;
}
public void dateTimePickDialog(final TextView inputDate, final String formatStr, final OnDateTimeSelectClickListener listener) {
new AlertDialog.Builder(activity)
.setPositiveButton("确定", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
if (onDateTimeSelectClickListener != null) {
onDateTimeSelectClickListener.onDateTimeSelectClick();
}
}
})
.setNegativeButton("取消", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int whichButton) {
}
}).show();
}
public interface OnDateTimeSelectClickListener {
void onDateTimeSelectClick();
}
}1
在 OnMapSearchPopupWindow.kt 中调用 dateTimePickDialog 方法
class OnMapSearchPopupWindow(var context: Context) : PopupWindow() {
var onDateTimePickListener: ((Boolean, String) -> Unit)? = null
private fun selectTime() {
val dialog = DateTimePickDialog(this)
//写法一(不推荐)
dialog.dateTimePickDialog(editor.editText, resFormat, object: DateTimePickDialog.OnDateTimeSelectClickListener{
override fun onDateTimeSelectClick() {
onDateTimePickListener?.invoke(isStartTime, editor.editText.text.toString())
}
})
//写法二
dialog.dateTimePickDialog(editor.editText, resFormat, {
onDateTimePickListener?.invoke(isStartTime, editor.editText.text.toString())
})
写法二在as会有个黄色波浪线的代码提示：Move lambda arguments out of parenthesis , 按代码提示后写法变为：
//写法三
dialog.dateTimePickDialog(editor.editText){
onDateTimePickListener?.invoke(isStartTime, editor.editText.text.toString())
}
}
}1
2
MainActivity.kt中 初始化 onDateTimePickListener
class MainActivity : Activity() {
private var mOnMapSearchPopupWindow: OnMapSearchPopupWindow? = null
override fun onCreate(savedInstanceState: Bundle?) {
mOnMapSearchPopupWindow = OnMapSearchPopupWindow(this)
mOnMapSearchPopupWindow?.onDateTimePickListener = { isStartTime, dateTime ->
if (isStartTime) {
mQueryPersonTypeReq.startTime = dateTime
} else {
mQueryPersonTypeReq.endTime = dateTime
}
mOnMapPresenter.queryPersonType(mQueryPersonTypeReq)
}
}
}1
2
3
### 8. kotlin中对于include子布局文件后的id引用：
activity_main.xml
<include android:id="@+id/toolBarInclude"
layout="@layout/base_toolbar"/>
1 | base_toolbar.xml |
<?xml version=”1.0” encoding=”utf-8”?>
<android.support.v7.widget.Toolbar xmlns:android=”http://schemas.android.com/apk/res/android"
xmlns:app=”http://schemas.android.com/apk/res-auto"
android:id=”@+id/toolBar”
android:layout_width=”match_parent”
android:layout_height=”42dp”
android:background=”@color/color_theme”
app:popupTheme=”@style/ThemeOverlay.AppCompat.Light”
app:subtitleTextAppearance=”@style/baseToolbarSubTitle”
app:theme=”@style/ThemeOverlay.AppCompat.Dark.ActionBar”
app:titleTextAppearance=”@style/baseToolbarTitle”>
</android.support.v7.widget.Toolbar>1
MainActivity如何使用ToolBar这个控件呢？
import kotlinx.android.synthetic.main.activity_main.*
private fun initToolbar() {
val myToolBar = (toolBarInclude as Toolbar)
myToolBar.title = getString(R.string.call_meeting_title)
myToolBar.setNavigationIcon(R.drawable.base_ic_arrow_toolbar)
myToolBar.setNavigationOnClickListener {
finish()
}
}1
2
3debug下程序就知道 toolBarInclude 就是个Toolbar对象，所以强转他就可以使用了
### 9. if语句判断变量为空就return java代码写法：
MXSession session = Matrix.getInstance(context).getDefaultSession();
if(session == null){
return;
}1
有4行代码，而用kotlin一行代码即可搞定：
val session = Matrix.getInstance(context).defaultSession ?: return`