java.lang.RuntimeException: Unable to instantiate activity ComponentInfo

You may be trying to find the view before onCreate() which is incorrect.

public class MainActivity extends Activity {

  ImageView mainImage = (ImageView) findViewById(R.id.imageViewMain); //incorrect

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

There is another way to get an java.lang.RuntimeException: Unable to instantiate activity ComponentInfo exception and that is the activity that you are trying to start is abstract. I made this stupid mistake once and its very easy to overlook.

In my case I forgot to add the google maps library

<application>
    ....

    <uses-library android:name="com.google.android.maps" />
</application>

Also, check that you're not missing the preceding dot before the activity path

<activity android:name=".activities.MainActivity"/>

This might not be relevant to the actual question, but in my instance, I tried to implement Kotlin and left out apply plugin: 'kotlin-android'. The error happened because it could not recognize the MainActivity in as a .kt file.

Hope it helps someone.

It also happens because of this issue. I unchecked the jars that needed be exported to the apk and this same thing happened. Please tick the jars that your app Needs to run.

I encountered this problem too, but in a slightly different way. Here was my scenario:

App detail:

• Using ActionBarSherlock as a library
• Using android-support-v4-r7-googlemaps.jar in the ActionBarSherlock library so I could use a "map fragment" in my primary project
• Added the jar to the build path of my primary project
• Included the <uses-library android:name="com.google.android.maps" /> in the manifests of both the library project and my primary project (this may not be necessary in the library?)
• The manifest in the primary project had the proper activity definition and all of the appropriate properties
• I didn't have an abstract activity or any of the other gotchas I've seen on Stack Overflow pertaining to this problem.

However, I still encountered the error described in the original post and could not get it to go away. The problem though, was slightly different in one regard:

• It only affected a fresh install of the application to my device. Any time the app installed for the first time, I would get the error preceded by several "warnings" of: Unable to resolve superclass of FragmentActivity
• Those warnings traced back to the ActionBarSherlock library
• The app would force close and crash.
• If I immediately rebuilt and redeployed the app, it worked fine.
• The only time it crashed was on a totally fresh install. If I uninstalled the app, built and deployed again from Eclipse, it would crash. Build/deploy a second time, it would work fine.

How I fixed it:

• In the ActionBarSherlock library project, I added the android-support-v4-r7-googlemaps.jar to the build path

• This step alone did not fix the problem

• Once the jar was added to the build path, I had change the order on the Java Build Path > Order and Export tab - I set the JAR to the first item in the list (it was the last after the /src and /gen items).

• I then rebuilt and redeployed the app to my device - it worked as expected on a fresh install. Just to be certain, I uninstalled it again 2-3 times and reinstalled - still worked as expected.

This may be a total rookie mistake, but I spent quite a while digging through posts and my code to figure it out, so hopefully it can be helpful to someone else. May not fix all situations, but in this particular case, that ended up being the solution to my problem.

This error can also be the ultimate sign of a dumb mistake (like when I - I mean, cough, like when a friend of mine who showed me their code once) where they try to execute code outside of a method like trying to do this:

SQLiteDatabase db = openOrCreateDatabase("DB", MODE_PRIVATE, null); //trying to perform function where you can only set up objects, primitives, etc

@Override
public void onCreate(Bundle savedInstanceState) {
....
}

rather than this:

SQLiteDatabase db;

@Override
public void onCreate(Bundle savedInstanceState) {
db = openOrCreateDatabase("DB", MODE_PRIVATE, null);
....
}

I got rid of this problem by deleting the Bin and Gen folder from project(which automatically come back when the project will build) and then cleaning the project from ->Menu -> Project -> clean.

Thanks.

For me, my package string in AndroidManifest.xml was incorrect (copied from a tutorial). Make sure the package string in this file is the same as where your main activity is, e.g.

 package="com.example.app"

An easy way to do this is to open the AndroidManifest.xml file in the "Manifest" tab, and type it in the text box next to Package, or use the Browse button.

Also, the package string for my activity was wrong, e.g.

<activity android:name="com.example.app.MainActivity" android:label="@string/app_name">

I (stupidly) got the same error weeks later when I renamed my package name. If you do this, make sure you update the AndroidManifest.xml file too.

Simply Clean your working project or restart eclipse. Then run your project. it will work.

In my case I haven't set the setContentView(R.layout.main);

If you create a new class do not foget to set this in on onCreate(Bundle savedInstanceState) method.

I have done this stupid mistake several times.

For me it was different from any of the above,

The activity was declared as abstract, That is why giving the error. Once it removed it worked.

Earlier

     public abstract class SampleActivity extends AppcompatActivity{
     }

After removal

     public class SampleActivity extends AppcompatActivity{
     }

Make sure MainActivity is not "abstract".

abstract class MainActivity : AppCompatActivity()

just remove the abstract

class MainActivity : AppCompatActivity() {

Ok, I am fairly experienced on the iPhone but new to android. I got this issue when I had:

Button infoButton = (Button)findViewById(R.id.InfoButton);

this line of code above:

@Override
public void onCreate (Bundle savedInstanceState) {
}

May be I am sleep deprived :P

In my case, I was trying to initialize the components(UI) even before the onCreate is called for the Activity.

Make sure your UI components are initialized/linked in the onCreate method after setContentView

NB: This is my first mistake while learning Android programming.

My problem was missing package declaration in the beginning of the activity source file:

package com.my.package

I recently encountered this with fresh re-install of Eclipse. Turns out my Compiler compliance level was set to Java 1.7 and project required 1.6.

In Eclipse: Project -> Properties -> Java Compiler -> JDK Compliance

This can happen if your activity class is inside a default package. I fixed it by moving the activity class to a new package. and changing the manifest.xml

before

activity android:name=".MainActivity" 

after

activity android:name="new_package.MainActivity"

This also happens when you type the wrong applicationId in the build.gradle file.

For eg. Your application ID is com.example.myapp.app

And you wrote build.gradle file like this:

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.1"

    defaultConfig {
        applicationId "com.example.myapp"
        //this will make your app crash so write exact applicationId as it is
        minSdkVersion 8
        targetSdkVersion 8
    }

Whow are there lots of ways to get this error!.

I will add another given none of the others either applied or were the cause.

I forgot the 'public' in the declaration of my activity class! It was package private.

I had been writing so much Bluetooth code that habit caused me to create an activity class that was package private.

Says something about the obscurity of this error message.

In my case I forget to make MainActivity class as public.

Other solutions:

1. Add activity in Manifest file

2. Verify all access modifiers

Got this problem, and fixed it by setting the "launch mode" property of the activity.

Another reason of this problem may be a missing library.

Go to Properties -> Android and check that you add the libraries correctly

I had the same problem, but I had my activity declared in the Manifest file, with the correct name.

My problem was that I didn't have to imported a third party libraries in a "libs" folder, and I needed reference them in my proyect (Right-click, properties, Java Build Path, Libraries, Add Jar...).

As suggested by djjeck in comment in this answer I missed to put public modifier for my class.

It should be

public class MyActivity extends AppCompatActivity {

It may help some like me.

This happens to me fairly frequently when using the NDK. I found that it is necessary for me to do a "Clean" in Eclipse after every time I do a ndk-build. Hope it helps anyone :)

This error also occurs when you use of ActionBarActivity but assigned a non AppCompat style.

To fix this just set your apps style parent to an Theme.AppCompat one like this.:

<!-- Base application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.Light">
    <!-- Customize your theme here. -->
</style>

Right click on project > properties > android > and try with different version of the android earlier i was doing with android 4.4 then i changed to android 4.3 and it worked !

Most the time If Activity name changed reflected all over the project except the AndroidManifest.xml file.

You just need to Add the name in manifest manually.

<activity
android:name="Activity_Class_Name"
android:label="@string/app_name">
</activity>