Develop Reference

Layout cannot be removed

I am trying to remove the layout when the apps starts.
I removed "setContentView" from the MainActivity.java file but still the layout is showing when the activty starts..
How can I remove the layout??
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setVisible(false);
}
}

try adding this to your manifest, inside activity android:theme="#android:style/Theme.Translucent.NoTitleBar.Fullscreen"

Android app without a layout

I'm a totally noob on Android, is there a way to execute an app without a layout? The process would be like: Click app icon -> run some code (Without prompting any window) -> display toast.

The trick is to open a transparent activity, show the toast and finish the activity, which makes it look like only the toast is displayed because the activity which opened was transparent.
To do this you can do.
public class MainActivity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Toast.makeText(this, messageToBeDisplayed, Toast.LENGTH_SHORT).show();
// finish the activity as soon as it opened.
this.finish();
}
}
Also you need to give a transparent theme to your activity by specifying it in AndroidManifest.xml, For which you can use NoDisplayeTheme provided by Android like this.
<activity android:name="TransparentActivity"
android:theme="#android:style/Theme.NoDisplay">
</activity>

Yes you can by adding:
android:theme="#android:style/Theme.NoDisplay"
in your activity in Android manifest.
Check this answer for more details.

Use this:
public class MainActivity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Toast.makeText(this, "", Toast.LENGTH_SHORT).show();
this.finish();
}
}
and in manifest file add: android:theme="#android:style/Theme.NoDisplay"

Trying to start a new Activity using Intent

I'm new to Android Dev, so please help me out.
I'm trying to start a new activity after i press a button but nothing seems to work.
Here's my code:
public class viewInfo extends Activity {
private Button btn;
public TextView txt;
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.info);
btn=(Button)findViewById(R.id.buy);
btn.setOnClickListener(new OnClickListener(){
#Override
public void onClick(View v) {
Intent myIntent = new Intent(viewInfo.this, buyNow.class);
startActivity(myIntent);
}
});
}
I've also added this new activity in the Manifest but it keeps crushing after I press the button.
What am I doing wrong?

Misread the question initially (original answer below for completeness sake).
Make sure you have the activity you are calling defined in your manifest file:
Something like
<activity android:name=".buyNow" android:label="#string/app_name"></activity>
within the application tags would suffice.
Here's the original answer.
Assuming that you have the correct button ID - try this in your onclick:
Intent myIntent = new Intent(getApplicationContext(), buyNow.class);
startActivity(myIntent);
You could add a log message inside your onClick too, to make sure it is actually being called. You can see the log from logcat (run via adb logcat on the command line)

Try to make it:
startActivity(new Intent("[Here is your package name.what you declared in Manifest file]"));
For this you need to write to your manifest:
Hope it helps.

There may be a problem with your buyNow activity that is causing the error.
You really need to use logcat to trace the error. You can enable this by clicking the menu item:
Window -> Show View -> Other...
the selecting "LogCat" from the Android folder

You can simply do this:
startActivity(new Intent(getBaseContext(),Activity.class));
Afther you registred your activity in manifest:
<activity
android:name="com.example.ActivityName"
android:label="#string/app_name" >
</activity>

New activity (screen) and "Application has stopped..."

in my app I am trying to add new screen. In my activity I've:
public void addItem(View v) {
Intent i = new Intent(SQLiteListActivity.this, add_screen.class);
startActivity(i);
}
In add_screen.java:
public class add_screen extends Activity {
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
TextView tv = new TextView(this);
tv.setText("Hello, Android");
setContentView(tv);
}
}
In file add_screen.xml I've layout this screen. In file AndroidManifest.xml I added this next activity, especially:
<activity class=".Add_screen" android:name="ADD_ITEM" android:label="Add item">
</activity>
I am still getting an error message about "Application has been stopped." I am newbie in Android development, I tried to do this by some tutorial, I've everything by it, but I don't know why, I'm still getting the error message above...
Can you help me, please, with this problem? I've no idea, what could be wrong.

Try replacing the activity tag in your manifest with this instead:
<activity
android:name=".add_screen"
android:label="Add item"
>
<intent-filter>
<category android:name="android.intent.category.DEFAULT"/>
</intent-filter>
</activity>
You shouldn't need the class attribute, I don't even know if that's recognized.
Edit: Try the above instead?

Android preferences problem

I am following this tutorial: link text
Preferences.java:
public class Preferences extends PreferenceActivity{
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.preferences);
}
}
PreferencesTutorial.java:
public class PreferencesTutorial extends Activity{
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Button prefBtn = (Button) findViewById(R.id.prefButton);
prefBtn.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
Intent settingsActivity = new Intent(getBaseContext(),
Preferences.class);
startActivity(settingsActivity);
}
});
}
}
Preferences.xml:
When application starts, and i click the prefButton, an error occures: "The application PreferencesTutorial (process PreferencesTutorial.com.examples) has stopped unexpectedly. Please try again"
I haven't found any mistakes in the code.
I would also like to show my filestructure if that helps:
AndroidManifest.xml:
What is wrong with the code?
Even if i add (where the cursor is)
<activity
android:name=".Preferences"
android:label="#string/set_preferences">
</activity>
i still get the error.

Try removing this import, if you have it;
import java.util.prefs.Preferences;

You have to mention this in your androidManifest.xml file
<activity
android:name=".Preferences"
android:label="#string/set_preferences">
<intent-filter>
<category android:name="android.intent.category.DEFAULT"/>
</intent-filter>
</activity>

You probably do not have Preferences defined in your manifest.
However, as others have indicated, use adb logcat, DDMS, or the DDMS perspective in Eclipse to examine LogCat and see the stack trace associated with your crash.

Is the error raised in the OnClick in PreferencesTutorial Class or onCreate in the preferences Class? Stick a couple of Log.d("Debug","%ID") in various locations and see which one doesn't get called.