Intent Service(使用Service來執行繁重的任務)

6 min readJun 25, 2018

使用Service來執行繁重的任務

假設今天要做繁重的任務，那就需要開一條Thread出去執行對吧~
但是有了IntentService，就可以使用將繁重任務交由service做了。

MainActivity在addTask使用了IntentService，那是一個static方法。
由它去啟動Service執行任務(下載圖片)。

class MainActivity : AppCompatActivity() {
    companion object {
        public val DOWNLOAD_RESULT = "Complete"
    }

    private val downloadReceiver = object : BroadcastReceiver() {
        override fun onReceive(context: Context?, intent: Intent?) {
            intent?.let {
                if (intent.action.equals(DOWNLOAD_RESULT)) {
                    var path = intent.getStringExtra(MyIntentService.EXTRA_PATH)
                    handleResult(path)
                }
            }
        }
    }

    fun handleResult(path: String) {
        var tv = textViewRoot.findViewWithTag<TextView>(path)
        tv.text = path + " download success ~~ "
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        registerReceiver()
        newBtn.setOnClickListener {
            addTask()
        }
    }

    fun registerReceiver() {
        var filter = IntentFilter()
        filter.addAction(DOWNLOAD_RESULT)
        registerReceiver(downloadReceiver, filter)
    }

    override fun onDestroy() {
        super.onDestroy()
        unregisterReceiver(downloadReceiver)
    }

    var i = 0
    fun addTask() {
        var path = "http://james/imags/" + (++i) + ".jpg"
        MyIntentService.startDownloadImage(this, path)
        var textView = TextView(this)
        textViewRoot.addView(textView)
        textView.text = path + " is download ..."
        textView.tag = path
    }
}

Service，繁重的任務會在onHandleIntent去執行，可以由接收的intent去判斷要執行什麼任務(下載圖片)。

這邊是用Broadcast去傳送資訊給MainActivity，顯示下載完成。

class MyIntentService : IntentService("MyIntentService") {
    companion object {
        val SERVICE_ACTION = "DownloadImage"
        val EXTRA_PATH = "Image"
        fun startDownloadImage(context: Context, path: String) {
            var i = Intent(context, MyIntentService::class.java)
            i.setAction(SERVICE_ACTION)
            i.putExtra(EXTRA_PATH, path)
            context.startService(i)
        }
    }

    override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
        Log.d("IntentServiceId", " " + startId)
        return super.onStartCommand(intent, flags, startId)
    }

    override fun onHandleIntent(intent: Intent?) {
        intent?.let {
            val action = intent.action
            if (SERVICE_ACTION.equals(action)) {
                val path = intent.getStringExtra(EXTRA_PATH)
                handleDownloadImage(path)
            }
        }
    }

    fun handleDownloadImage(path: String) {
        try {
            Thread.sleep(2000)
            var i = Intent(MainActivity.DOWNLOAD_RESULT)
            i.putExtra(EXTRA_PATH, path)
            sendBroadcast(i)
        } catch (e: InterruptedException) {
            e.printStackTrace()
        }
    }

    override fun onCreate() {
        super.onCreate()
        Log.d("IntentService", " onCreate")
    }

    override fun onDestroy() {
        super.onDestroy()
        Log.d("IntentService", " onDestroy")
    }
}