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No Activity found to handle Intent for Default Activity

I get error No Activity found to handle Intent when I try to start Default Activity from another Activity using
Intent start = new Intent("com.name.name.MainActivity");
startActivity(start);
finish();
I guess this is because in AndroidManifest for Default Activity I have android.intent.action.MAIN
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
Is there a way to start Default Activity from another Activity when Default Activity is finished before?

You are trying to start the activity using the action name..
Note:startActivity() always adds CATEGORY_DEFAULT to an Intent if there is no other category specified(Here you have no category specified in your internt so its default).
Hence, an <intent-filter> for an <activity> always needs a <category>, whether DEFAULT or something else (here it needs default that's why error says No Activity found to handle Intent for Default Activity)
The LAUNCHER category says that this entry point should be listed in the application launcher.
The DEFAULT category is required for the Context.startActivity() method to resolve your activity when its component name is not explicitly specified.
Try to specify two intent filters:
<activity android:name=".MyActivity"
android:configChanges="orientation|keyboardHidden"
android:windowSoftInputMode="stateHidden"
android:screenOrientation="portrait">
<intent-filter>
<action android:name="android.intent.action.MAIN"/>
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
<intent-filter>
<action android:name="com.name.name.MainActivity"/>
<category android:name="android.intent.category.DEFAULT"/>
</intent-filter>
</activity>
Then you can start the activity using the action name:
Intent intent = new Intent("com.name.name.MainActivity");
startActivity(intent);
or simply you can go with the class name:
Intent intent = new Intent(context, MainActivity.class);
startActivity(intent);

Intent i = new Intent(otheractivity.this, MainActivity.class);
startActivity(i);

Launch a new screen (activity) instead of replacing the crurent one

My first App
This is my first android app - QR Code Scanner using ZXingScanner Library.
Is there any way to launch a new screen (activity) instead of replacing the crurent one, so i can press back from the scanner to go back to main screen where is the button?
Please help me. Thanks all

I think that this site can help you: http://developer.android.com/training/basics/firstapp/starting-activity.html
In short words:
You need to create new
Intent myIntent = new Intent(this, SecondActivity.class) and than start it by startActivity(myIntent).
Additionally it will be good to define your MAIN activity in AndroidManifest.
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>

You should create 2 activities in your app.
From first activity send an intent to the second activity that you created before (I think that you can create one). With sending an intent to another activity the first one remain, and you can use back button to load that.
Now this is the easiest way that you can send an intent:
Intent intent= new Intent(Activity1.this,Activity2.class);
startActivity(intent);
But there is some other ways to send an activity(similar to this one):
How to start new activity on button click

how to make our activity page open from another application?

I am new in android development, I want to build a music player but the problem in front of me is how do i make my app open from gallery.
For example,
if we want to open any music file then we select it, the the android mobile ask which player do we want to use.
so how can I add my app in that option.
please help.

If you want your app to be in the list for opening an audio file, you need to tell the system your app can open those files. You can do that by adding something like the following to your activity tag in your AndroidManifest.xml:
<intent-filter>
<action android:name="android.intent.action.VIEW" />
<category android:name="android.intent.category.DEFAULT" />
<data android:scheme="content"/>
<data android:scheme="file"/>
<data android:mimeType="audio/*"/>
<data android:mimeType="application/ogg"/>
<data android:mimeType="application/x-ogg"/>
<data android:mimeType="application/itunes"/>
</intent-filter>
Intent filters are part of the core principles in Android development. You should try to get some knowledge on these basic topics before getting started.

It helps you
Intent intent = new Intent();
intent.setAction(android.content.Intent.ACTION_VIEW);
File file = new File(YOUR_SONG_URI);
intent.setDataAndType(Uri.fromFile(file), "audio/*");
startActivity(intent);

Actually you can open activity not app at self just simply add action intent filter in mainfest like this
<activity class=".foo" android:label="#string/title_notes_list">
<intent-filter>
<action android:name="com.me.love" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
other app code :
Intent intent = new Intent("com.me.love");
startActivity(intent);
however if you want to tell android system that your activity can handle some actions like share or send data you just have to add "send" action to your activity in mainfest like so :
<activity class=".boo" android:label="#string/title_notes_list">
<intent-filter>
<action android:name="android.intent.action.SEND" />
<category android:name="android.intent.category.DEFAULT" />
<data android:mimeType="text/plain" />
</intent-filter>
</activity>
so now when ever user click share button android system will check all activitys that have action string "android.intent.action.SEND" then give the user list of activitys that have send action and if you did added same action as boo activity dose to your activity then it will be one of chooses in the list.

Reading value of android:scheme programmatically

I want to know if it is possible to read the value of android:scheme from the Android-manifest-file (example below) programmatically.
<intent-filter>
<action android:name="android.intent.action.VIEW" />
<category android:name="android.intent.category.DEFAULT" />
<category android:name="android.intent.category.BROWSABLE" />
<data android:scheme="zxtest" />
</intent-filter>

You should be able to get this information from the PackageManager:
PackageManager pm = getPackageManager();
ActivityInfo activityInfo = pm.getActivityInfo(component,
PackageManager.GET_INTENT_FILTERS);
Unfortunately, however, you can't :-( This call SHOULD return the intent filters (according to the documentation), but it seems that the Android developers haven't gotten around to actually implementing it yet :-(
See Unable to get intent filters from a package

I'm assuming you mean that the intent has been called and you're trying to find the scheme from your activity's code?
In your activity's onCreate method, you can do the following:
Intent intent = getIntent();
Uri data = intent.getData();
String scheme = data.getScheme(); // "zxtest"

Launching Intent cannot find Activity

My program has a list of tabs that each contain a list of people. Clicking a person should edit their details, but instead, clicking a person throws an ActivityNotFoundException. My code that starts the edit activity:
Intent intent = new Intent("my.package.EDIT"); // Person is both
intent.putExtra("my.package.PERSON", (Parcelable) myPerson); // Parcelable and
GroupArrayAdapter.this.getContext().startActivity(intent); // Serializable
Relevant part of AndroidManifest.xml:
<activity android:name="EditActivity">
<intent-filter>
<action android:name="my.package.EDIT" />
</intent-filter>
</activity>
What's going on?

There's two ways to start an Activity, either explicitly or implicitly. Explicitly means that you use the class name directly; usually if you're calling an Activity that is within your own application, what you mean to use is the explicit method because it's far easier:
Intent intent = new Intent(context, EditActivity.class);
context.startActivity(intent);
However, if you really do mean to use implicit filtering, then your intent filter is missing something. Every implicit intent filter requires the category android.intent.category.DEFAULT (with few exceptions). Try this and see if it works:
<activity android:name="EditActivity">
<intent-filter>
<category android:name="android.intent.category.DEFAULT" />
<action android:name="my.package.EDIT" />
</intent-filter>
</activity>
Suggested reading: intent filters.

When you instantiate your Adapter, pass the context from the calling activity. Then in your adapter use context.startActivity(...);