Android 中的通知示例

通知是一种消息、警报或应用程序的状态（可能在后台运行），在 Android 的 UI 元素中可见或可用。此应用程序可能在后台运行，但用户未使用。通知的目的是通知用户有关由用户或系统在应用程序中启动的进程。本文可以帮助那些努力为开发目的创建通知的人。

通知可以是各种格式和设计，具体取决于开发人员。一般而言，您必须目睹这四种类型的通知：

1. 状态栏通知（显示在与当前时间、电池百分比相同的布局中）
2. 通知抽屉通知（出现在下拉菜单中）
3. 提醒通知（出现在覆盖屏幕上，例如：Whatsapp 通知、OTP 消息）
4. 锁屏通知（我猜你知道）

在本文中，我们将讨论如何在Kotlin中生成通知。

分步实施

第 1 步：创建一个新项目

要在 Android Studio 中创建新项目，请参阅如何在 Android Studio 中创建/启动新项目。请注意，选择Kotlin作为编程语言。

第 2 步：使用 activity_main.xml 文件

转到activity_main.xml文件并参考以下代码。在这一步中，我们将设计我们的布局页面。在这里，我们将使用 RelativeLayout 从 Kotlin 文件中获取 Scroll View。下面是activity_main.xml文件的代码。

第 3 步：创建一个新的空活动

Reference article: How to Create Constructor, Getter/Setter Methods and New Activity in Android Studio using Shortcuts? 

将活动命名为afterNotification 。当有人点击通知时，此活动将在我们的应用程序中打开，用户将被重定向到此页面。下面是activity_after_notification.xml文件的代码。

Note 1: Without configuring Notification Channels, you cannot build notification for applications with Android API >=26. For them generating a notification channel is mandatory. Apps with API<26 don’t need notification channels they just need notification builder. Each channel is supposed to have a particular behavior that will be applicable to all the notifications which are a part of it. Every channel will, therefore, have a Channel ID which basically will act as a unique identifier for this Channel which will be useful if the user wants to differentiate a particular notification channel. In contrast, the Notification builder provides a convenient way to set the various fields of a Notification and generate content views using the platform’s notification layout template but is not able to target a particular notification channel. 

Note 2: If you have referred any other documentation or any other blog before this one, you might have noticed them appealing to implement the following dependency“com.android.support:support-compat:28.0.0”. What I’ve personally experienced is that there’s no need to implement it, things go far and good without this also.

第 5 步：使用 MainActivity.kt 文件

转到MainActivity.kt文件并参考以下代码。下面是MainActivity.kt文件的代码。代码中添加了注释以更详细地理解代码。

科特林

import android.app.Notification
import android.app.NotificationChannel
import android.app.NotificationManager
import android.app.PendingIntent
import android.content.Context
import android.content.Intent
import android.graphics.BitmapFactory
import android.graphics.Color
import android.os.Build
import android.os.Bundle
import android.widget.Button
import android.widget.RemoteViews
import androidx.appcompat.app.AppCompatActivity
 
class MainActivity : AppCompatActivity() {
 
    // declaring variables
    lateinit var notificationManager: NotificationManager
    lateinit var notificationChannel: NotificationChannel
    lateinit var builder: Notification.Builder
    private val channelId = "i.apps.notifications"
    private val description = "Test notification"
 
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
 
        // accessing button
        val btn = findViewById(R.id.btn)
 
        // it is a class to notify the user of events that happen.
        // This is how you tell the user that something has happened in the
        // background.
        notificationManager = getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
 
        // onClick listener for the button
        btn.setOnClickListener {
 
            // pendingIntent is an intent for future use i.e after
            // the notification is clicked, this intent will come into action
            val intent = Intent(this, afterNotification::class.java)
 
            // FLAG_UPDATE_CURRENT specifies that if a previous
            // PendingIntent already exists, then the current one
            // will update it with the latest intent
            // 0 is the request code, using it later with the
            // same method again will get back the same pending
            // intent for future reference
            // intent passed here is to our afterNotification class
            val pendingIntent = PendingIntent.getActivity(this, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT)
 
            // RemoteViews are used to use the content of
            // some different layout apart from the current activity layout
            val contentView = RemoteViews(packageName, R.layout.activity_after_notification)
 
            // checking if android version is greater than oreo(API 26) or not
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                notificationChannel = NotificationChannel(channelId, description, NotificationManager.IMPORTANCE_HIGH)
                notificationChannel.enableLights(true)
                notificationChannel.lightColor = Color.GREEN
                notificationChannel.enableVibration(false)
                notificationManager.createNotificationChannel(notificationChannel)
 
                builder = Notification.Builder(this, channelId)
                        .setContent(contentView)
                        .setSmallIcon(R.drawable.ic_launcher_background)
                        .setLargeIcon(BitmapFactory.decodeResource(this.resources, R.drawable.ic_launcher_background))
                        .setContentIntent(pendingIntent)
            } else {
 
                builder = Notification.Builder(this)
                        .setContent(contentView)
                        .setSmallIcon(R.drawable.ic_launcher_background)
                        .setLargeIcon(BitmapFactory.decodeResource(this.resources, R.drawable.ic_launcher_background))
                        .setContentIntent(pendingIntent)
            }
            notificationManager.notify(1234, builder.build())
        }
    }
}

有了这个，我们现在已经成功地为我们的应用程序创建了一个“通知”。请注意，上面代码中列出的参数是必需的，缺少任何单个参数都可能导致应用程序崩溃或无法启动。内容标题、内容文本、小图标是可自定义的参数，但也是必需的。可以根据需要更改它们的值。

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