Android App Crashing at setSupportActionBar

Question

I'm trying to follow the following tutorial to create a tab view layout: http://www.android4devs.com/2015/01/how-to-make-material-design-sliding-tabs.html

Unfortunately, the app kept crashing before anything came up. After inserting debug logs into my code, I found that the problem resided in the line setSupportActionBar(toolbar) in MainActivity. I have no idea why this is happening. I have pasted my entire MainActivity file below.

package com.example.rkhaj.tabstest;

import android.support.v4.view.ViewPager;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;


public class MainActivity extends AppCompatActivity {

    // Declaring Your View and Variables

    Toolbar toolbar;
    ViewPager pager;
    ViewPagerAdapter adapter;
    SlidingTabLayout tabs;
    CharSequence Titles[]={"Home","Events"};
    int Numboftabs =2;

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

        Log.d("icecream", "position 1");


        // Creating The Toolbar and setting it as the Toolbar for the activity

        toolbar = (Toolbar) findViewById(R.id.tool_bar);
        Log.d("icecream", "position 1.5");
        setSupportActionBar(toolbar);

        Log.d("icecream", "position 2");


        // Creating The ViewPagerAdapter and Passing Fragment Manager, Titles fot the Tabs and Number Of Tabs.
        adapter =  new ViewPagerAdapter(getSupportFragmentManager(),Titles,Numboftabs);

        Log.d("icecream", "position 3");

        // Assigning ViewPager View and setting the adapter
        pager = (ViewPager) findViewById(R.id.pager);
        pager.setAdapter(adapter);

        Log.d("icecream", "position 4");

        // Assinging the Sliding Tab Layout View
        tabs = (SlidingTabLayout) findViewById(R.id.tabs);
        tabs.setDistributeEvenly(true); // To make the Tabs Fixed set this true, This makes the tabs Space Evenly in Available width

        Log.d("icecream", "position 5");

        // Setting Custom Color for the Scroll bar indicator of the Tab View
        tabs.setCustomTabColorizer(new SlidingTabLayout.TabColorizer() {
            @Override
            public int getIndicatorColor(int position) {
                return getResources().getColor(R.color.tabsScrollColor);
            }
        });

        Log.d("icecream", "position 6");

        // Setting the ViewPager For the SlidingTabsLayout
        tabs.setViewPager(pager);

        Log.d("icecream", "position 7");



    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        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();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

This is activity_main.xml:

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

    <include
        android:id="@+id/tool_bar"
        layout="@layout/tool_bar"
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        />

    <com.example.rkhaj.tabstest.SlidingTabLayout
        android:id="@+id/tabs"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:elevation="2dp"
        android:background="@color/ColorPrimary"/>

    <android.support.v4.view.ViewPager
        android:id="@+id/pager"
        android:layout_height="match_parent"
        android:layout_width="match_parent"
        android:layout_weight="1"
        >
    </android.support.v4.view.ViewPager>

</LinearLayout>

This is the logcat:

09-07 16:46:27.772  22833-22833/com.example.rkhaj.tabstest I/art﹕ Late-enabling -Xcheck:jni
09-07 16:46:27.772  22833-22833/com.example.rkhaj.tabstest I/art﹕ VMHOOK: rlim_cur : 0 pid:22833
09-07 16:46:27.812  22833-22833/com.example.rkhaj.tabstest E/Typeface﹕ SANS_LOC file not found.
09-07 16:46:27.882  22833-22833/com.example.rkhaj.tabstest D/icecream﹕ position 1
09-07 16:46:27.882  22833-22833/com.example.rkhaj.tabstest D/icecream﹕ position 1.5
09-07 16:46:27.882  22833-22833/com.example.rkhaj.tabstest E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.example.rkhaj.tabstest, PID: 22833
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.rkhaj.tabstest/com.example.rkhaj.tabstest.MainActivity}: java.lang.IllegalStateException: This Activity already has an action bar supplied by the window decor. Do not request Window.FEATURE_SUPPORT_ACTION_BAR and set windowActionBar to false in your theme to use a Toolbar instead.
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2411)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2474)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1359)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:155)
            at android.app.ActivityThread.main(ActivityThread.java:5696)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1029)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:824)
     Caused by: java.lang.IllegalStateException: This Activity already has an action bar supplied by the window decor. Do not request Window.FEATURE_SUPPORT_ACTION_BAR and set windowActionBar to false in your theme to use a Toolbar instead.
            at android.support.v7.app.AppCompatDelegateImplV7.setSupportActionBar(AppCompatDelegateImplV7.java:197)
            at android.support.v7.app.AppCompatActivity.setSupportActionBar(AppCompatActivity.java:99)
            at com.example.rkhaj.tabstest.MainActivity.onCreate(MainActivity.java:34)
            at android.app.Activity.performCreate(Activity.java:5958)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1129)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2364)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2474)
            at android.app.ActivityThread.access$800(ActivityThread.java:144)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1359)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:155)
            at android.app.ActivityThread.main(ActivityThread.java:5696)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1029)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:824)
09-07 16:46:39.442  22833-22833/com.example.rkhaj.tabstest D/Process﹕ killProcess, pid=22833
09-07 16:46:39.442  22833-22833/com.example.rkhaj.tabstest D/Process﹕ com.android.internal.os.RuntimeInit$UncaughtHandler.uncaughtException:138 java.lang.ThreadGroup.uncaughtException:693 java.lang.ThreadGroup.uncaughtException:690

Answer 1

Since you are using a Toolbar in your layout, you should use Theme.AppCompat.NoActionBar as your parent theme.

Otherwise you can use somenthing like:

<style name="MyTheme" parent="Theme.AppCompat">
    ...
</style>

<style name="MyTheme.NoActionBar">
    <!-- Both of these are needed -->
    <item name="windowActionBar">false</item>
    <item name="windowNoTitle">true</item>
</style>