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Default Page will not change

My home page needs to show two buttons: login & register. The page Login Activity with both buttons should appear first, but only the register screen comes up.
I am very new to coding. So, please be nice :( I've been stuck on this for days.
Below is the AndroidManifest.xml. Can anyone spot what I am doing wrong?
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.thrd">
<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/AppTheme">
<activity android:name=".LoginActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".RegisterActivity"></activity>
<activity android:name=".UserAreaActivity"></activity>
</application>
</manifest>

You manifest file is ok. Probably you have some logical errors in your code. In LoginActivity. So it launches RegisterActivity (probably in onCreate), instead of showing itself.

No activity found to handle Intent/no launcher activity found manifest file issue

Here's the problem guys, first i tried to run my application with Launch default activity as launch action (Run Configurations --> Android --> Launch action), the logcat kept telling me that it can't find the launcher activity and the application wouldn't even start, problem is i defined my launcher activity in the manifest file, but it's like it's not reading it at all.
So i tried to launch the splash activity by specifically telling it to run it through run configurations, it did launch but during the transition to the next activity it crashed again, the logcat says no activity found to handle intent, which again, I defined the way I did in other applications and worked alright there. Plase help it's a nightmare.
Here's the code for the MainActivity:
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Thread timer = new Thread()
{
public void run(){
try{
sleep(6000);
} catch (InterruptedException e){
e.printStackTrace();
} finally {
Intent openStarting = new Intent("totaltrainer.com.WorkoutPlace");
startActivity(openStarting);
}
}
};
timer.start();
}
#Override
protected void onPause() {
// TODO Auto-generated method stub
super.onPause();
finish();
}
}
And Manifest:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="totaltrainer.com"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="15" />
<application
android:allowBackup="true"
android:icon="#drawable/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="totaltrainer.com.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".WorkoutPlace"
android:label="#string/app_name" >
<intent-filter>
<action android:name="totaltrainer.com.WorkoutPlace" />
</intent-filter>
</activity>
<activity
android:name=".WorkoutHome"
android:label="#string/app_name" >
<intent-filter>
<action android:name="totaltrainer.com.WorkoutHome" />
</intent-filter>
</activity>
<activity
android:name=".WorkoutGym"
android:label="#string/app_name" >
<intent-filter>
<action android:name="totaltrainer.com.WorkoutGym" />
</intent-filter>
</activity>
</application>
</manifest>

use "totaltrainer.com.WORKOUTGYM" and so on
and below use this
<category android:name="android.intent.category.DEFAULT" />

Problem 1
logcat kept telling me that it can't find the launcher activity and
the application wouldn't even start
In your Manifest file, change below
<activity
android:name=".MainActivity"
android:label="#string/app_name" >
<intent-filter>
<action android:name="totaltrainer.com.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
as
<activity android:name="MainActivity">
<!-- This activity is the main entry, should appear in app launcher -->
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
What happens when you define this Action and Category ?
The ACTION_MAIN action indicates this is the main entry point and does not expect any intent data.
The CATEGORY_LAUNCHER category indicates that this activity's icon should be placed in the system's app launcher. If the element does not specify an icon with icon, then the system uses the icon from the element.
These two must be paired together in order for the activity to appear in the app launcher.
Problem 2
the logcat says no activity found to handle intent
Your Manifest declaration seems fine.
In your activity class, change
Intent openStarting = new Intent("totaltrainer.com.WorkoutPlace");
startActivity(openStarting);
as
Intent openStarting = new Intent();
openStarting.setAction("totaltrainer.com.WorkoutPlace");
startActivity(openStarting);

Android: I added another button but now the app crashes

I added another button to my app but now the app crashes on start up. Here is the code that I added in, when I block it out the app runs fine.
btnnext.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
startActivity(new Intent("com.com.com.addtask"));
}
});
}
I think it might be a problem with the manifest so here is the manifest too (and this is only a playing around app so dont hassle me about the package being com.com.com)
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.com.com"
android:versionCode="1"
android:versionName="1.0">
<uses-sdk android:minSdkVersion="8" />
<uses-permission android:name="android.permission.INTERNET"/>
<application android:icon="#drawable/ic_launcher" android:label="#string/app_name" android:permission="android.permission.INTERNET">
<activity android:name=".HelloWorldActivity"
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=".addtask"
android:label="#string/app_name">
<intent-filter>
<action android:name="com.com.com.addtask" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
</application>
</manifest>
And this might be helpful too:
05-16 21:21:55.446: E/AndroidRuntime(581): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.com.com/com.com.com.HelloWorldActivity}: java.lang.NullPointerException

Have you declared the new button that you have added within the activity?
Button btnnext = (Button)findViewById(R.id.myNewButton);
If you don't do this and set a listener it will throw the nullpointer error.

First identify the button from xml to activity using
Button b = (Button) findViewById(R.id.btnNext);

androidManifest and intent-filter to order activity

I have 3 Activity in my androidManifest,
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="zepod.whatelsecomics" android:versionCode="1"
android:versionName="1.0">
<uses-sdk android:minSdkVersion="8" />
<application android:icon="#drawable/icon" android:label="#string/app_name">
<activity android:name=".Activity1"
android:label="#string/list1">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".Activity2"
android:label="#string/list2">
</activity>
<activity android:name=".Activity3"
android:label="#string/addItemToList2">
</activity>
</application>
The first one call the second one
The second one call the third one
The first one activity is the main activity.
The result of the third one activity is an updated list in the second one (just a form).
But now, if i clik the back button i came back at the third one
How can i force the app to came back at the first activity?
I suppose this depend by androidManifest but i don't understand the intent-filters order
Can someone help me?

When starting to the third activity, call finish() to remove the second activity from the stack. That's the easiest way.
There are other ways. This question has been asked a million times on SO, search for it and you'll find alternatives.

Problem calling activity from another package in Android

Situation:
I need to combine several apps into one .apk app. Lets say implement app2 into app1
What i have done:
Copied app2 package into main app1 project which i am working, so my app1 has two packages.
app2 had this manifest file:
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.package.app2" android:versionCode="3" android:versionName="1.2">
<application android:label="App2" android:icon="#drawable/icon">
<activity android:name="Activity1" android:launchMode="singleTask">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name="Activity2" android:excludeFromRecents="true"></activity>
</application>
<uses-permission android:name="android.permission.WAKE_LOCK"></uses-permission>
<uses-permission android:name="android.permission.VIBRATE"></uses-permission>
</manifest>
My original App1 manifest file:
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.package.app1">
<application android:icon="#drawable/icon" android:debuggable="true">
<activity android:name=".Start" 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="com.package.app1.PlayerList" />
<activity android:name="com.package.app1.CreateNewPlayer" />
<activity android:name="com.package.app1.Profile" />
<activity android:name="com.package.app1.Braintrainer" />
</application>
</manifest>
The code in app1 i am using to call activity in app2 package:
Intent i = new Intent();
i.setClassName("com.package.app1", "com.package.app2.Activity1");
startActivity(i);
The question:
How do i modify my app1 manifest file to have activities of app2.
Things i`ve tried:
It works if i create simple HelloWorld test class in app2, call using the same code and just include this in the app1 manifest:
<activity android:name="com.package.app2.Test" />
But i can not figure out how to implement the app2 manifest file into the first one. Every way i try give no errors but crashes when calling that activity. App2 alone works fine, so problem not in the activity file.
Appreciate any thoughts on this.

Intent i = new Intent();
i.setClassName("com.package.app1", "com.package.app2.Activity1");
startActivity(i);
Shot in the dark:
change com.package.app1 to com.package.app2. I've called done what you're attempting right now, and I've always had to specify the package of the class I wanted to call.
Ok, PackageManager is not your solution, I misread and thought you had two apps and wanted one app to call the other. It looks like you just want one app.
Modify your app1's manifest like this:
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.package.app1">
<application android:icon="#drawable/icon" android:debuggable="true">
<activity android:name=".Start" 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="com.package.app2.Activity1" />
<activity android:name="com.package.app2.Activity2" android:excludeFromRecents="true"></activity>
<activity android:name="com.package.app1.PlayerList" />
<activity android:name="com.package.app1.CreateNewPlayer" />
<activity android:name="com.package.app1.Profile" />
<activity android:name="com.package.app1.Braintrainer" />
</application>
<uses-permission android:name="android.permission.WAKE_LOCK"></uses-permission>
<uses-permission android:name="android.permission.VIBRATE"></uses-permission>
</manifest>
And try the first way again.

I have several packages and need to do something similar in my app.
You need to be careful with this technique, otherwise you'll experience nasty memory leaks.
I declared my activity in my base controller (activity) class as a static variable. All controller classes inherit from this class, so all controller classes are able to access it. Pass in the activity as an argument for anything outside of the controller classes that need to access the activity.