My android app stops unexpectedly, How to debug in android studio?

Question

Since, I am new to android. I don't understand methods to debug my application. My app stops working as soon as I try opening it. I am trying to create a sidebar or navigation drawer.

Here's my layout:

<android.support.v4.widget.DrawerLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent">


    <!-- The first child in the layout is for the main Activity UI-->
    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:paddingLeft="@dimen/activity_horizontal_margin"
        android:paddingRight="@dimen/activity_horizontal_margin"
        android:paddingTop="@dimen/activity_vertical_margin"
        android:paddingBottom="@dimen/activity_vertical_margin"
        tools:context=".MainActivity"
        android:background="#ffffffff">


        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerHorizontal="true"
            android:text="Holy Operating Systems, Batdroid!"
            android:textSize="24sp"
            android:gravity="center"
            android:layout_marginTop="100dp"/>


        <ImageView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:src="@drawable/batdroid"
            android:layout_alignParentBottom="true"
            android:layout_centerHorizontal="true"/>


    </RelativeLayout>


    <!-- Side navigation drawer UI -->
    <ListView
        android:id="@+id/navList"
        android:layout_width="200dp"
        android:layout_height="match_parent"
        android:layout_gravity="left|start"
        android:background="#ffeeeeee"/>


</android.support.v4.widget.DrawerLayout>

Here's the mainActivity code:

package ems.pixelapp.com.ems;


        import android.content.res.Configuration;
        import android.os.Bundle;
        import android.support.v4.widget.DrawerLayout;
        import android.support.v7.app.ActionBarActivity;
        import android.support.v7.app.ActionBarDrawerToggle;
        import android.view.Menu;
        import android.view.MenuItem;
        import android.view.View;
        import android.widget.AdapterView;
        import android.widget.ArrayAdapter;
        import android.widget.ListView;
        import android.widget.Toast;




public class MainActivity extends ActionBarActivity {


    private ListView mDrawerList;
    private DrawerLayout mDrawerLayout;
    private ArrayAdapter<String> mAdapter;
    private ActionBarDrawerToggle mDrawerToggle;
    private String mActivityTitle;


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


        mDrawerList = (ListView)findViewById(R.id.navList);
        mDrawerLayout = (DrawerLayout)findViewById(R.id.drawer_layout);
        mActivityTitle = getTitle().toString();


        addDrawerItems();
        setupDrawer();


        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        getSupportActionBar().setHomeButtonEnabled(true);
    }


    private void addDrawerItems() {
        String[] osArray = { "Android", "iOS", "Windows", "OS X", "Linux" };
        mAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, osArray);
        mDrawerList.setAdapter(mAdapter);


        mDrawerList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Toast.makeText(MainActivity.this, "Time for an upgrade!", Toast.LENGTH_SHORT).show();
            }
        });
    }


    private void setupDrawer() {
        mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout, R.string.drawer_open, R.string.drawer_close) {


            /** Called when a drawer has settled in a completely open state. */
            public void onDrawerOpened(View drawerView) {
                super.onDrawerOpened(drawerView);
                getSupportActionBar().setTitle("Navigation!");
                invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
            }


            /** Called when a drawer has settled in a completely closed state. */
            public void onDrawerClosed(View view) {
                super.onDrawerClosed(view);
                getSupportActionBar().setTitle(mActivityTitle);
                invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
            }
        };


        mDrawerToggle.setDrawerIndicatorEnabled(true);
        mDrawerLayout.setDrawerListener(mDrawerToggle);
    }


    @Override
    protected void onPostCreate(Bundle savedInstanceState) {
        super.onPostCreate(savedInstanceState);
        // Sync the toggle state after onRestoreInstanceState has occurred.
        mDrawerToggle.syncState();
    }


    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        mDrawerToggle.onConfigurationChanged(newConfig);
    }


    @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;
        }


        // Activate the navigation drawer toggle
        if (mDrawerToggle.onOptionsItemSelected(item)) {
            return true;
        }


        return super.onOptionsItemSelected(item);
    }
}

Here's the error I am getting, due to which my app has stopped working

01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime: FATAL EXCEPTION: main
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime: java.lang.RuntimeException: Unable to start activity ComponentInfo{ems.pixelapp.com.ems/ems.pixelapp.com.ems.MainActivity}: java.lang.NullPointerException
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2355)
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2391)
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at android.app.ActivityThread.access$600(ActivityThread.java:151)
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1353)
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:99)
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:155)
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5559)
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at java.lang.reflect.Method.invokeNative(Native Method)
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Method.java:511)
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1074)
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:841)
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at dalvik.system.NativeStart.main(Native Method)
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:  Caused by: java.lang.NullPointerException
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at ems.pixelapp.com.ems.MainActivity.onCreate(MainActivity.java:45)
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at android.app.Activity.performCreate(Activity.java:5066)
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1102)
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2311)
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2391) 
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at android.app.ActivityThread.access$600(ActivityThread.java:151) 
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1353) 
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:99) 
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:155) 
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5559) 
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at java.lang.reflect.Method.invokeNative(Native Method) 
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Method.java:511) 
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1074) 
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:841) 
01-13 16:24:51.807 11270-11270/ems.pixelapp.com.ems E/AndroidRuntime:     at dalvik.system.NativeStart.main(Native Method)

When you look the stacktrace you can see it happens due to this: *Caused by: java.lang.NullPointerException ... at ems.pixelapp.com.ems.MainActivity.onCreate(MainActivity.java:45)* (which say you have a `NullPointerException` in `onCreate()` from `MainActivity.java`, line `45`). You should indicate the line in the file by editing your question. — fllo, Jan 13 '16 at 11:03
Hello Fllo and gabriele, my line no 45 has a this code getSupportActionBar().setDisplayHomeAsUpEnabled(true); — topsy coder, Jan 13 '16 at 11:05
Possible duplicate of [What is a Null Pointer Exception, and how do I fix it?](http://stackoverflow.com/questions/218384/what-is-a-null-pointer-exception-and-how-do-i-fix-it) — yennsarah, Jan 13 '16 at 11:07
There you go.. Without ActionBar `getSupportActionBar()` will return `null`. — Roshan, Jan 13 '16 at 11:21
@Roshan I changed the AppTheme.NoActionBar to AppTheme.AppBarOverlay But still app is not running — topsy coder, Jan 13 '16 at 11:28
I think AppTheme.AppBarOverlay is meant to be used with ToolBar. Try AppTheme.Base — Roshan, Jan 13 '16 at 11:53

score 2 · Answer 1 · answered Jan 13 '16 at 11:54

2

as @Roshan pointed out, I was using a theme which does not support getSupportActionBar().

I changed my theme to Theme.AppCompat, and it worked like a charm.

answered Jan 13 '16 at 11:54

topsy coder

105
3
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My android app stops unexpectedly, How to debug in android studio?

1 Answers1