Example from SDK C:\Program Files\Android\android-sdk-windows\samples\android-10\ApiDemos\src\com\example\android\apis\text\Link.java
Source: //developer.android.com/resources/browser.html?tag=sample
License: //www.apache.org/licenses/LICENSE-2.0
1.) Automatically linkifies using android:autoLink="all"

// res/values/strings.xml
<string name="link_text_auto"><b>text1:</b> This is some text.  In
      this text are some things that are actionable.  For instance,
      you can click on //www.google.com and it will launch the
      web browser.  You can click on google.com too.  And, if you
      click on (415) 555-1212 it should dial the phone.
    </string>
// main.xml
<!-- text1 automatically linkifies things like URLs and phone numbers. -->
  <TextView xmlns:android="//schemas.android.com/apk/res/android"
            android:id="@+id/text1"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:autoLink="all"
            android:text="@string/link_text_auto"
            />

2.) Link text by setMovementMethod

// MainActivity.java onCreate
/*Be warned that if you want a TextView with a key listener or movement method not to be focusable, or if you want a TextView without a key listener or movement method to be focusable, you must call setFocusable(boolean) again after calling this to get the focusability back the way you want it. */

TextView t2 = (TextView) findViewById(R.id.text2);
t2.setMovementMethod(LinkMovementMethod.getInstance());

// main.xml
<!-- text2 uses a string resource containing explicit <a> tags to
       specify links. -->
  <TextView xmlns:android="//schemas.android.com/apk/res/android"
            android:id="@+id/text2"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:text="@string/link_text_manual"
            />

//strings.xml

<string name="link_text_manual"><b>text2:</b> This is some other
      text, with a <a href="//www.google.com">link</a> specified
      via an <a> tag.  Use a \"tel:\" URL
      to <a href="tel:4155551212">dial a phone number</a>.
    </string>

3.) Link as html code using Html.fromHtml()

// MainActivity.java onCreate
        TextView t3 = (TextView) findViewById(R.id.text3);
        t3.setText(
            Html.fromHtml(
                "<b>text3:</b>  Text with a " +
                "<a href=\"//www.google.com\">link</a> " +
                "created in the Java source code using HTML."));
        t3.setMovementMethod(LinkMovementMethod.getInstance());

4.) Link string by SpannableString

        SpannableString ss = new SpannableString(
            "text4: Click here to dial the phone.");

        ss.setSpan(new StyleSpan(Typeface.BOLD), 0, 6,
                   Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
        ss.setSpan(new URLSpan("tel:4155551212"), 13, 17,
                   Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);

        TextView t4 = (TextView) findViewById(R.id.text4);
        t4.setText(ss);
        t4.setMovementMethod(LinkMovementMethod.getInstance());

Change table row background color if user click on row Android example code.
MainActivity.java

public class MainActivity extends Activity {
Boolean bColorYellow = true;
TextView hTextView;
TableRow hTableRow;
@Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        hTextView = (TextView)findViewById(R.id.idTextView);
        hTableRow = (TableRow)findViewById(R.id.idTableRow1);


        
        
    } // end onCreate
  
    
    public void myTableRowClickHandler(View view) {
		switch (view.getId()) {
		case R.id.idTableRow1:{
			
			if(bColorYellow){
			hTableRow.setBackgroundColor(Color.GREEN);
			bColorYellow = false;
			}
			else{
			hTableRow.setBackgroundColor(Color.YELLOW);
			bColorYellow = true;
			}
		}
		break;
		}
  }
}

main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="//schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >


<TableLayout android:layout_height="wrap_content" android:layout_width="fill_parent" android:id="@+id/tableLayout1">
    <TableRow android:id="@+id/idTableRow1" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:background="#5655AA"
    android:onClick="@string/myTableRowClick"
    android:focusable="true">
<TextView  
	android:id="@+id/idTextView"
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="@string/hello"
    />
    
    </TableRow>
</TableLayout>
    
    
</LinearLayout>

strings.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string name="hello">Hello World!</string>
    <string name="app_name">TableRow</string>
    <string name="myTableRowClick">myTableRowClickHandler</string>
</resources>

Button, setOnClickListener, Intent.ACTION_VIEW, startActivity Android example.

Button mIdButtonHome = (Button)findViewById(R.id.idButtonHome);
	mIdButtonHome.setOnClickListener(new View.OnClickListener() {
		public void onClick(View v) {
			Intent browserIntent = new Intent(
					Intent.ACTION_VIEW,
					Uri.parse("//android.okhelp.cz/category/software/"));
			startActivity(browserIntent);
		}
	});

Emulator window was out of view and was recentred
Emulator] WARNING: Data partition already in use. Changes will not persist!
Emulator] WARNING: SD Card image already in use: C:\Documents and Settings\user_name\.android\avd\hvga21_up1_7.avd/sdcard.img
Emulator] WARNING: Cache partition already in use. Changes will not persist!

Basic step
Try restart Eclipse if using from menu File->Restart

Other solutions

Solution 1: try restart ADB server
//android.okhelp.cz/how-quickly-restart-adb-exe-adb-server-android-emulator-example/


Solution 2:

Delete Run Configuration

//android.okhelp.cz/android-emulator-wont-run-application-started-from-eclipse/





Solution 3:
Try delete:

c:\Documents and Settings\user_name\.android\avd\my_avd.avd\cache.img
c:\Documents and Settings\user_name\.android\avd\my_avd.avd\userdata-qemu.img

Try solution 4:
Eclipse menu select Window->Preferences->Android

Windows 32

FROM: C:\Program Files\Android\android-sdk
TO: C:\PROGRA~1\Android\android-sdk

Windows 64

FROM: C:\Program Files (x86)\Android\android-sdk
TO: C:\PROGRA~2\Android\android-sdk

UNEXPECTED TOP-LEVEL EXCEPTION:
java.lang.IllegalArgumentException: already added: Lcz/okhelp/MyMathClass;

First try this solution!!!!!
Select your project in project tree and go to the Eclipse menu Project » Clean » Clean projects selected below » select your project and click OK.

If you create *.apk package with proguard sometimes you must back up the project, delete project, and create new project if you are unable to create *.apk file.

Check your AndroidManifest.xml if all Activity is correctly inserted. If you add a library project to Main project you have to insert Activity from library to Main project AndroidManifest.xml


Problem with the library.
I deleted library project from project tree and again put the _library project into the main project. This problem was resolved.
1.)Go to Project » Properties » Java Build Path » Libraries and remove (your projects) click OK.
2.)Go to Project » Clean » Clean projects selected below » select your project and click OK.
3.)Add again your LIBRARY project to your MAIN project Project » Properties » Java Build Path » Libraries.
See image below.

Problem with a *.apk file
If you create signed *.apk, you have to delete previous *.apk from your PC folder.