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Can't resolve symbol 'SecondActivity' Validates resource references inside Android XML files

I'm new to Android Application development. I just added another activity tag in my AndroidManifest.xml file but its gives me the following message : Can't resolve symbol 'SecondActivity' Validates resource references inside Android XML files.
I want to know why is this message getting displayed?
Here is my AndroidManifest.xml file :
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.aupadhyay.myfirstapp">
<application
android:allowBackup="true"
android:icon="#mipmap/amiticon"
android:label="#string/app_name"
android:supportsRtl="true"
android:theme="#style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".SecondActivity">
<intent-filter>
<action android:name="anything" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
</application>
</manifest>
And this is my SecondActivity.java file :
import android.support.v7.app.AppCompatActivity;
public class SecondActivity extends AppCompatActivity {
}
Picture :

Consider the following:
Remove the intent-filter inside your second activity unless you really need that.
In your second activity, override onCreate method
#override
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.second_activity_layout);
}
Did you create a layout for your second activity? It seems your activity is empty - although this might not be the cause of your problem. Also what is the location of your SecondActivity, a different package or in the same place as the first activity?
As shown in your code, your second activity doesn't seem to have any of that layout stuff!
I hope this helps you!

It seems your SecondActivity doesn't belongs to the package "com.aupadhyay.myfirstapp", So move it to src of the "com.aupadhyay.myfirstapp" package where ever it currently belongs to.

How to use a different launcher activity in a product flavor?

I'm working on an Android library project, in the default src/main/AndroidManifest.xml, the MainActivity is the launcher activity.
For the sake of something else, I created product flavors. Yes, it works perfect if I want to trigger / show different activitis inside different product flavors. However, I wanna keep the default launcher activity from src/main/ folder, while register another flavored activity as the new launcher activity. So that for different product flavors, I could have different launcher activities, and from them I could still start original "launcher" activity in src/main/.
Could anyone kindly tell me how to achive that? Thanks a lot.
Notes:
Adding if (BuildConfig.FLAVOR.equals("flavorName")) code to original launcher activity is not prefered. Because I don't want to modify the production code from someone else (this is a library project).
I've tried manifestmerger and tools:replace, but seems like it doesn't work for intent-filter (I noticed that the element merging policy for intent-filter is always).
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
If this may work, could you please kindly guide me how to make it work? Thanks.

What I have tried:
Enabling Manifest Merger, which doesn't work;
Using activity-alias, which doesn't work either.
Finally I found out that the problem could be solved by just adding one line:
<category android:name="android.intent.category.DEFAULT" />
==================================================
To make it clear, I'll go through the problem and solution one more time:
Under src/main/java there is a MainActivity, and in corresponding src/main/AndroidManifest.xml it specifies MainActivity as the launcher activity:
<activity android:name=".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>
That is a very easy part. Now we start with the product flavor part.
Due to some reason, in a product flavor, I don't want to overwrite the MainActivity, instead, I have a YetAnotherMainActivity. The goal is to set the YetAnotherMainActivity as the new launcher activity in the product flavor, and it should still be able to call MainActivity.
And here, is how you can set the new activity in product flavor as the new launcher activity:
flavorX/AndroidManifest.xml:
<activity android:name="com.example.YetAnotherMainActivity"
android:label="#string/title_yet_another_main_activity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
Yep, it turns out deadly easy. Just add android.intent.category.DEFAULT.

I think that <activity-alias> fits there more than any other solution (have no idea why #JingLi couldn't get it working. Maybe there were some troubles year ago, but for now it's okay).
For example, we have the following manifest in main:
<manifest
xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.application">
<application>
<activity android:name=".InfoActivity"/>
<activity-alias
android:name="com.example.application.Launcher"
android:targetActivity=".InfoActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN"/>
<category android:name="android.intent.category.LAUNCHER"/>
</intent-filter>
</activity-alias>
</application>
</manifest>
And we want to replace launcher activity with DebugInfoActivity from debug flavor. So, we need to just replace the targetActivity attribute in the specified <activity-alias> tag:
<manifest
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools">
<application>
<activity android:name=".DebugInfoActivity"/>
<!-- to not litter the manifest -->
<activity
android:name="com.example.application.InfoActivity"
tools:node="remove"/>
<activity-alias
android:name="com.example.application.Launcher"
android:targetActivity=".DebugInfoActivity"
tools:replace="android:targetActivity"/>
</application>
</manifest>
Notes:
In the example we use the same package name for main and debug.
We have to enter the full name for activity-alias, so the merger can merge their correctly.
With the solution we also can inherit all attributes and childs from main activity-alias to not duplicate their in debug.

I guess I am not late :)
So today I got the same problem. #seroperson solution was correct but If you do not want the default launcher activity at all then just use the below code in your flavor's manifest:
<activity
android:name=".DefaultLauncherActivity"
tools:node="remove"
>

Android merger is merging intent-filter from main manifest lancher to flavors. I have not found way to prevent that. You end up with 2 app icons on device (each for launcher Activity).
Based on that, you cannot override completely settings from main manifest. Solition may be to keep only shell of manifest in main folder and implement manifest in each flavor or to remove conflict Activities from main folder and implemenent independently in each flavor.
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
package="com.adamassistant.app">
<!-- empty shell, implementation in flavors folders -->
</manifest>

The simplest and cleanest solution is to keep only one Manifest and write two different MainActivity.java class one for each flavor in order to avoiding duplication of manifest nodes.
Given two flavors in gradle
productFlavors {
paid {
packageName "com.example"
}
demo {
packageName "com.example.demo"
}
}
Given this project structure
app/
|--libs/
|--src/
|--paid/
| |--java/
| |--com/example/
| |--MainActivity.java
|--demo/
| |--java/
| |--com/example/
| |--MainActivity.java
|--main/
|--java/
| |--...
|--res/
| |--...
|--AndroidManifest.xml
And this Android Manifest
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.flavors">
<application
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme">
<activity
android:name=".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>

Create a different AndroidManifest.xml file in your flavor. And there set your DifferentFlavorMainActivity.java as the launcher activity with full name like:
android:name="com.android.application.paid.MainActivity"

The working simplest solution is to use manifest merging and using
<intent-filter tools:node="removeAll">
as suggested in the following post :
Merging android manifest files, conflicting filter

Daydream settings

I'm trying to create a settings for my Daydream and according to the documentation, I need to create a xml file, like this:
<dream xmlns:android="http://schemas.android.com/apk/res/android"
android:settingsActivity="com.example.app/.MyDreamSettingsActivity" />
However, my Activity is in a library project (called com.project.base) and I keep getting this error in Logcat when clicking on the setting button:
11-16 23:01:29.331: E/AndroidRuntime(28908): android.content.ActivityNotFoundException: Unable to find explicit activity class {com.project.base/com.project.base.SettingsDayDream}; have you declared this activity in your AndroidManifest.xml?
I have my xml file setup like this:
<dream xmlns:android="http://schemas.android.com/apk/res/android"
android:settingsActivity="com.project.base/.SettingsDayDream" />
but I've tried all variation, such as com.project.base/com.project.base.SettingsDayDream
and just com.project.base.SettingsDayDream, but nothing seems to work.
I've declared the activity in the AndroidManifest.xml like this:
<activity android:name="com.project.base.SettingsDayDream" android:configChanges="keyboardHidden|orientation" />
as well as the service:
<service android:name="com.project.base.DayDream" android:exported="true" android:icon="#drawable/icon" android:label="#string/app_name">
<intent-filter>
<action android:name="android.service.dreams.DreamService" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
<meta-data android:name="android.service.dream" android:resource="#xml/daydream" />
</service>

The problem is in your daydream.xml. The format for the android:settingsActivity is current.app.package/com.project.base.SettingsActivity
So current.app.package, before the /, needs to be your current app, not the library project.

Reorganizing activities in different folders

I want to change the structure of my android application to have the activites in a subfolder called activities. So, my code structure will become
com.example.myapp.activities.MainActivity
and all the activities will reside within com.example.myapp.activities
How do I achieve this ? Also, What changes will have to be made in the manifest for this to work ? How will I access other activity classes from within other activities ?
<activity
android:name=".activities.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>
EDIT : I achieved this using dragging and dropping the activities in the folders but now I am getting this error on setContentView(R.layout.main); : main cannot be resolved or is not a
field

If you organize all activities in same packages, then you have to define the activity without package declaration in Manifest file, example
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.myapp.activities"
android:versionCode="1"
android:versionName="1.0" >
<application
android:icon="#drawable/ic_launcher"
android:label="#string/app_name"
android:name=".WorldClockApplication"
<activity
android:name=".WorldClockHomeActivity"
android:label="#string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".AddLocationActivity"/>
<activity android:name=".EditPreference"/>
</application>
</manifest>
Then you should call that activity inside another activity using intent. Consider I'm calling WorldClockHomeActivity from WorldClockApplication activity as follows:
Intent myIntent=new Intent(WorldClockApplication.this,WorldClockHomeActivity.class);
startActivity(myIntent);
Then do clean, refresh your project you wont get error in your project. If get error on
setContentView(R.layout.main);
that means you have problem in res/strings or res/layout or res/drawable folders not in manifest file

If you are using Eclipse create a new packet in your project and drag and drop your activities files in there. Eclipse will take care of all the necessary changes.
The changes are in your directory structure and in the manifest as you have posted in the question.
Activities can be launched (or new Intents can be sent to them) as usual through Intent(context, YourActivity.class);
I wouldn't move the activities though, rather I'd organize other Java classes in separate packages.

Android error "unable to find explicit activity class"

I have an android project with several packages. The structure of the packages in this case is com.WAPP.SetLocation is the package that contains the activity I want to run.
In my manifest, com.WAPP is considered the base package:
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.WAPP"
android:versionCode="1"
android:versionName="1.0">
My activities are declared in my manifest as:
<activity android:name=".mainScreenActivity"></activity>
<activity android:name=".SetLocation.setLocationActivity"></activity>
The mainScreen activity displays fine, since it is inside the com.WAPP package. But when I try to run the setLocationActivity, I get the unable to find explicit class error. Here is how I have the intent parameters:
Intent i = new Intent();
i.setClassName("com.WAPP.SetLocation",
"com.WAPP.SetLocation.setLocationActivity");
startActivity(i);

The first parameter is application package not the package where the activity is.
You can invoke the Activity like this.
Intent i = new Intent();
i.setClassName("com.WAPP",
"com.WAPP.SetLocation.setLocationActivity");
startActivity(i);
It is preferred as SYLARRR suggested to have Android automatically figure that out for you. Hence the call as..
startActivity(new Intent(this, setLocationActivity.class));
It's recommended per java standards to have the package name all lower-cased and the class name as CamelCased.

If the new activity not in the same packet with MainActivity(you call from here?), try declare on manifest
<activity android:name="com.WAPP.SetLocation.setLocationActivity"></activity>
and in the caller
Intent intent = new Intent(this, setLocationActivity.class);
startActivity(intent);
Hope this helps!

In additional to the above answers make sure that your activities are declared inside application in manifest
<application
android:allowBackup="true"
android:label="#string/app_name"
android:supportsRtl="true">
<activity android:name=".mainScreenActivity"></activity>
<activity android:name=".SetLocation.setLocationActivity"></activity>
</application>

If i'm not mistaken, the i.setClassName("com.WAPP.SetLocation","com.WAPP.SetLocation.setLocationActivity"); should be i.setClassName(getBaseContext(),"setLocationActivity"); Reference
Also try this syntax:
startActivity(new Intent(MyActivity.this, setLocationActivity.class));
and try removing the starting dot from:
<activity android:name=".SetLocation.setLocationActivity"></activity>

Do it by this way:
Intent intent = new Intent();
intent.setComponent(
new ComponentName("com.WAPP", "com.WAPP.SetLocation.setLocationActivity"));
startActivity(i);

you should class ad to manifest.xml
for example of manifest.xml
in this example, i added SecondActivity.class
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.myapplication">
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:roundIcon="#mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="#style/Theme.MyApplication">
<activity
android:name=".MainActivity"
android:exported="true">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".SecondActivity"
android:exported="true">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>

In Xamarin Android, make sure that your Activity class has an Activity attribute
[Activity(Theme = "#style/MyTheme")]
public class MyActivity : ActivityBase
{
...
}
With that you are making sure that your activity is registered in AndroidManifest.xml

I had the same kind of issue in the project . It wasted me almost a full day . i tried all the solutions that are mentioned above , but none of the solutions worked for me .
After all the hard work i just "Rebuild" the project and "clean" The project and it worked perfectly .
Note:
Before going through all the process u just needed to have a try to these options.

First of all, make sure that you have created activity and not the class. And, if it is activity then go to the manifest.xml file and look at the path of that particular file.
This worked for me absolutely well!!
https://forums.xamarin.com/discussion/104102/android-content-activitynotfoundexception-unable-to-find-explicit-activity-class
this is for reference

in your manifest you declared it as
.SetLoction.setLocationActivity
but
the package name is com.WAPP.SetLocation
so you need to prefix that again.
Intent i = new Intent();
i.setClassName("com.WAPP.SetLocation",
"com.WAPP.SetLocation.SetLocation.setLocationActivity");
startActivity(i);

This might be due to not registering your next activity XML file in the manifest. Register your next activity XML file in the AndroidManifest.xml file
<activity android:name=".NextActivity" />
Hope it helps.

Thia might be problem if ImageView is used :(
Intent intent = new Intent(context,ImageView.class);
intent.putExtra("imageurl",clients_document_return.getUrl());
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
v.getContext().startActivity(intent);
and your class name might me Imageview.class
so first check all small capital in class name
Thanks :)