asynctask code added

maciej-nowak · maciej-nowak · commit 0b0222e5dedd · 2019-04-09T20:28:27.000+02:00
diff --git a/asynctask/CustomAsyncTask.kt b/asynctask/CustomAsyncTask.kt
@@ -0,0 +1,34 @@
+//first of generic types are params, second progress and third is final result
+private class CustomAsyncTask : AsyncTask<String, Int, String>() {
+
+    override fun onPreExecute() {
+        //prepare before running background job like show progress dialog
+    }
+
+    override fun doInBackground(vararg params: String): String {
+        //some background job with passed params like URLs
+        var total = ""
+        for((counter, url) in params.withIndex()) {
+            //download info from url
+            val result = "result from : $url\n"
+            total = total.plus(url)
+            publishProgress(counter) //inform that some part of full request if completed
+        }
+        return total
+    }
+
+    override fun onProgressUpdate(vararg values: Int?) {
+        //show some progress updates based on Int from publishProgress
+    }
+
+    override fun onPostExecute(result: String) {
+        //do something on main thread when background job finished like update view
+    }
+
+    override fun onCancelled() {
+        //stop and clear or show some message
+    }
+}
+
+//to start just call
+//CustomAsyncTask().execute("url1", "url2", "url3")
diff --git a/asynctask/MainActivity.kt b/asynctask/MainActivity.kt
@@ -0,0 +1,81 @@
+class MainActivity : AppCompatActivity(), Listener {
+    
+    //reference to task allows to manage it's lifecycle
+    private var asyncTask : SaferAsyncTask? = null
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        setContentView(R.layout.activity_main)
+		
+        button.setOnClickListener {
+            //AsyncTask is single shot, so create new task every time
+            if(asyncTask == null || asyncTask?.status != AsyncTask.Status.RUNNING) {
+                asyncTask = SaferAsyncTask(this)
+                asyncTask?.execute("url1", "url2", "url3")
+            }
+        }
+    }
+
+    override fun onDestroy() {
+        //stop the task when exit from Activity
+        if(asyncTask?.status == AsyncTask.Status.RUNNING)
+            asyncTask?.cancel(true)
+        super.onDestroy()
+    }
+
+    override fun onStarting() {
+        //create progress dialog
+    }
+
+    override fun onProgress(progress: Int) {
+        //update progress dialog
+    }
+
+    override fun onFinished(result: String) {
+        //close progress dialog
+        //show the result
+    }
+
+    override fun onCancel() {
+        //close progress dialog
+        //show error message
+    }
+
+    private class SaferAsyncTask(listener : Listener) : AsyncTask<String, Int, String>() {
+
+        private val reference = WeakReference<Listener>(listener)
+
+        override fun onPreExecute() {
+            reference.get()?.onStarting()
+        }
+
+        override fun doInBackground(vararg params: String): String {
+            var total = ""
+            for((counter, url) in params.withIndex()) {
+                val result = "result from : $url\n"
+                total = total.plus(result)
+                publishProgress(counter) //inform that some part of full request if completed
+            }
+            return total
+        }
+
+        override fun onProgressUpdate(vararg values: Int?) {
+            values[0]?.let { reference.get()?.onProgress(it) }
+        }
+
+        override fun onPostExecute(result: String) {
+            reference.get()?.onFinished(result)
+        }
+
+        override fun onCancelled() {
+            reference.get()?.onCancel()
+        }
+    }
+}
+
+private interface Listener {
+    fun onStarting()
+    fun onProgress(progress : Int)
+    fun onFinished(result : String)
+    fun onCancel()
+}
diff --git a/asynctask/README.md b/asynctask/README.md
@@ -0,0 +1,2 @@
+# asynctask
+This is repository of http://androidcode.pl blog. It shows uses AsyncTask in Android. It is a part of Background processing - AsyncTask post in the blog.

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	`+# asynctask`
	`2`	`+This is repository of http://androidcode.pl blog. It shows uses AsyncTask in Android. It is a part of Background processing - AsyncTask post in the blog.`