title: Android: Error while installing APKs
body: <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>