What is causing this runnable thread to be skipped

Question

I have attempted to follow the examples that I have found on implementing a runnable thread, but for some reason the code is skipped.

For the sake of having a better understanding, can someone tell me what is preventing the thread code from executing?

MainActivity.java:

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.app.ActionBarActivity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class MainActivity extends ActionBarActivity {

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

        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment()).commit();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        String textinfo = "";

        getMenuInflater().inflate(R.menu.main, menu);
        TextView tv = (TextView) findViewById(R.id.infotext);
        textinfo += "Testing Android Runnable Thread.\n";
        tv.setText(textinfo);

        Runnable runnable = new Runnable() {
            public void run() {

                Global.classtext += "Running in thread!\n";

                long endTime = System.currentTimeMillis() + 20 * 1000;

                while (System.currentTimeMillis() < endTime) {
                    synchronized (this) {
                        try {
                            wait(endTime - System.currentTimeMillis());
                        } catch (Exception e) {
                        }
                    }

                }
            }
        };

        Thread mythread = new Thread(runnable);
        mythread.start();

        textinfo += Global.classtext;
        textinfo += "Finished.\n";
        tv.setText(textinfo);

        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main, container,
                    false);
            return rootView;
        }
    }
}

fragment_main.xml:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical"
     >

    <TextView
        android:id="@+id/infotext"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/infotext" />
</LinearLayout>

strings.xml:

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <string name="app_name">Andorid Thread Test</string>
    <string name="action_settings">Settings</string>
    <string name="infotext">Android Thread Test</string>
</resources>

AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.apollo.androidThreadtest"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="19" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.apollo.androidmysqltest.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

The code doesn't produce any errors. It runs on the android with the output:

Testing Androd Runnable Thread. Finished.

The lines in the thread ("Running in thread!") never displays and debug shows the whole block is skipped.

Answer 1

Since you are running a different thread, you cannot expect the code to execute sequentially like:

        Thread mythread = new Thread(runnable);
        mythread.start();

        textinfo += Global.classtext;
        textinfo += "Finished.\n";
        tv.setText(textinfo);

        return true;

By the time the main thread hits return true, Global.classtext may have not been changed by the parallel thread yet

To see what I mean, try changing your code to this:

            Thread mythread = new Thread(runnable);
            mythread.start();

            while(mythread.isAlive()){
                //wait till thread finishes
            }

            textinfo += Global.classtext;
            textinfo += "Finished.\n";
            tv.setText(textinfo);

            return true;