android笔记

• 根据uri获取文件真实路径

     /**
     * 根据uri获取文件真实路径
     */
    private fun getPathFromUri(ctx: Context, uri: Uri): String? {
        if (DocumentsContract.isDocumentUri(ctx, uri)) {
            val docId = DocumentsContract.getDocumentId(uri)
            when (uri.authority?.toLowerCase()) {
                "com.android.externalstorage.documents" -> {
                    val arr = docId.split(":")
                    if (arr[0] == "primary") {
                        return "${Environment.getExternalStorageDirectory()}/${arr[1]}"
                    }
                }
                "com.android.providers.downloads.documents" -> {
                    val contentUri =
                        ContentUris.withAppendedId(Uri.parse("content://downloads/public_downloads"), docId.toLong())
                    return queryPathFromUri(ctx, contentUri, null, null)
                }
                "com.android.providers.media.documents" -> {
                    val arr = docId.split(":")
                    val contentUri: Uri? = when (arr[0]) {
                        "image" -> MediaStore.Images.Media.EXTERNAL_CONTENT_URI
                        "video" -> MediaStore.Video.Media.EXTERNAL_CONTENT_URI
                        "audio" -> MediaStore.Audio.Media.EXTERNAL_CONTENT_URI
                        else -> null
                    }
                    contentUri?.let {
                        return queryPathFromUri(ctx, it, "_id=?", arrayOf(arr[1]))
                    }
                }
            }
        } else if (uri.scheme == "content") {
            return queryPathFromUri(ctx, uri, null, null)
        } else if (uri.scheme == "file") {
            return uri.path
        }
        return null
    }

    /**
     * 根据uri查询文件真实路径
     */
    private fun queryPathFromUri(context: Context, uri: Uri, selection: String?, selectionArgs: Array<String>?): String? {
        val column = "_data"
        val projection = arrayOf(column)
        context.contentResolver.query(uri, projection, selection, selectionArgs, null)?.let {
            if (it.moveToFirst()) {
                return it.getString(it.getColumnIndex(column))
            }
            it.close()
        }
        return null
    }

• 在fragment中模拟返回栈
  在FragmentTransaction中添加addToBackStack()

• 判断是否平板

fun isPad(): Boolean{
	val mCtx = MyApplication.getContext()
	if(mCtx != null){
		return (mCtx.resources.configuration.screenLayout and Configuration.SCREENLAYOUT_SIZE_MASK) >= Configuration.SCREENLAYOUT_SIZE_LARGE
	}
	return false
}

• service
  • Android Foreground Service (前台服务)
  • 【Android】Service那点事儿
• 按back键仅切换到后台而不退出

override fun onKeyDown(keyCode: Int, event: KeyEvent?): Boolean {
	if(keyCode == KeyEvent.KEYCODE_BACK){
		val home = Intent(Intent.ACTION_MAIN)
		home.flags = Intent.FLAG_ACTIVITY_CLEAR_TOP
		home.addCategory(Intent.CATEGORY_HOME)
		startActivity(home)
		return true
	}
	return super.onKeyDown(keyCode, event)
}

• 按2次back键退出

private var mExitTime = 0L
override fun onKeyDown(keyCode: Int, event: KeyEvent?): Boolean {
	if(keyCode == KeyEvent.KEYCODE_BACK){
		if((System.currentTimeMillis() - mExitTime) > 2000){
			Toast.makeText(this, "再按一次退出", Toast.LENGTH_SHORT).show()
			mExitTime = System.currentTimeMillis()
		}else{
			finish()
		}
		return true
	}
	return super.onKeyDown(keyCode, event)
}

• activity的4种启动模式(standard|singleTop|singleTask|singleInstance)

<activity android:name=".MainActivity"
	android:launchMode="singleInstance">
	<intent-filter>
		<action android:name="android.intent.action.MAIN"/>
		<category android:name="android.intent.category.LAUNCHER"/>
	</intent-filter>
</activity>

• 在子线程中new Handler时报错--Can't create handler inside thread that has not called Looper.prepare()

Looper.prepare()
Handler().postDelayed({
    // todo
}, 1000)
Looper.loop()

• Notification API的兼容性（用support-v4库的NotificationCompat类）

val manager = getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
var intent = Intent(this, MainActivity::class.java)
val pi = PendingIntent.getActivity(this, 0, intent,0)
val notify = NotificationCompat.Builder(this)
	.setContentTitle("title")
	.setContentText("content")
	.setSmallIcon(R.mipmap.ic_launcher)
	.setWhen(System.currentTimeMillis())
	.setContentIntent(pi)
	.setDefaults(NotificationCompat.DEFAULT_ALL)
	// 重要程度 -2, -1, 0, 1, 2
	.setPriority(NotificationCompat.PRIORITY_MAX)
	.setAutoCancel(true)
	.build()
manager.notify(1, notify)