Android: Error while installing APKs : <p>I'm slowly trying to do some simple tasks in <code>Android Studio</code>. The following app is installed on emulator without any errors. But when I tried to install it on a real device Redmi 3S this error occured:</p>

<pre><code>Unknown failure (Failure - not installed for 0)
Error while Installing APKs
</code></pre>

<p>I went through similar questions around here but in these cases the error was caused by not enabled debugging, or not accepitng the app instalation. However, I allowed debugging and I also tried to install <strong>some other app</strong> in Studio and it <strong>worked fine</strong>.</p>

<p>So the question probably is, what's wrong with the code.</p>

<blockquote>
  <p>MainActivity.java</p>
</blockquote>

<pre><code>package tlacitko.button;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    public void sendMessage(View view) {
        new Thread(new Runnable() {
            public void run() {

                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        try{
                            URL url = new URL("http://147.32.186.51:8080");
                           // HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
                            InputStream is = url.openStream();
                            BufferedReader br = new BufferedReader(new
                                    InputStreamReader(is));
                            String s = "";
                        }catch(MalformedURLException ex){

                        }catch(IOException e){
                        }
                    }
                });
            }
        }).start();
    }
}
</code></pre>

<p>And the xml code:</p>

<blockquote>
  <p>activity_main.xml
  
      </p>
</blockquote>

<pre><code>    &lt;TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Try to connect the server."
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" /&gt;

    &lt;Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="16dp"
        android:layout_marginRight="7dp"
        android:layout_marginTop="16dp"
        android:onClick="sendMessage"
        android:text="Conncect"
        app:layout_constraintLeft_toRightOf="@+id/editText"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" /&gt;


&lt;/android.support.constraint.ConstraintLayout&gt;
</code></pre>
