tag should specify a target API level Warning

RadioButton RadioGroup Android example source code for Android developer
Example for *.xml files

       <RadioGroup android:id="@+id/idRadio_group"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginLeft="20dp"
            android:orientation="vertical">

            <RadioButton android:id="@+id/idRadio_1"
                android:text="@string/textLabel_1"/>
            <RadioButton android:id="@+id/idRadio_2"
                android:text="@string/textLabel_2"/>
            <RadioButton android:id="@+id/idRadio_3"
                android:text="@string/textLabel_3"/>

        </RadioGroup>

Example for *.java files

// import
import android.widget.RadioGroup;
// get handle of RadioGroup
RadioGroup  mRadioGroup = (RadioGroup) findViewById(R.id.idRadio_group);

// which RadioButton is selected for example in some function body
         int nUnits = 10; // decimetry
    	 int nIdRadio = mRadioGroup.getCheckedRadioButtonId();
    			if(nIdRadio == R.id.idRadio_1) nUnits = 1; // metr
    			else if(nIdRadio == R.id.idRadio_2) nUnits = 10; // decimetr
    			else if(nIdRadio == R.id.idRadio_3) nUnits = 100; // cm
    			else if(nIdRadio == R.id.idRadio_4) nUnits = 1000; // mm


// listener for RadioGroup Java Android example
       mRadioGroup.setOnCheckedChangeListener(
                new RadioGroup.OnCheckedChangeListener() {
                    public void onCheckedChanged(RadioGroup group,
                            int checkedId) {
                        Log.v("Selected", "New radio item selected: " + checkedId);
                        recordNewUIState();
                    }
                });

getContext() getApplicationContext() method Java Android example source

Context myContext_1 = ThisClassName.this; // to open a Dialog

Context myContext_2 = getContext();

Context myContext_3 = this.getContext();

Context myContext_4 = this;

Context myContext_5 = this.getApplicationContext ();





	OnClickListener getImageBtnOnClick = new OnClickListener() {

		public void onClick(View view) {

			Context context = view.getContext();



		}

	};

// Toast 

Toast.makeText(getApplicationContext(), "Context == getApplicationContext "

   , Toast.LENGTH_SHORT).show();







// store Context in public class

public class MyActivity extends Activity { 

    public static Context myCnt = null; 

    ... 

    protected void onCreate(Bundle icicle) { 

         ... 

        myCnt = this; 

        MyStorage.setContext(myCnt); 

        // or

        // MyStorage.setContext(this);        

        

        // cntxFromStorage == this

        Context cntxFromStorage = MyStorage.getContext();

        ... 

        }; 

    }; 

    

public class MyStorage

{

    private static Context cntStorageContext = null;

 	  

     

    public static Context getContext() { 

        return cntStorageContext;

     }

        

    public static void setContext(Context context) {

	 MyStorage.cntStorageContext = context;

	  }





    }; 



class DataBaseHelper extends SQLiteOpenHelper {

// get MyActivity context 

Context cnt = MyStorage.getContext();



}

Try this solutions:
1.) Save xml file
2.) Close tab with xml file
3.) Reopen xml file

1.) Open from menu Window->Android SDK Manager
2.) Select available updates (Tools, SDK etc.)
3.) Install updates

1.) Open from menu Help->Check for Updates
2.) Install available plugins what You need
3.) Restart Eclipse

1.) check your xml files in res/layout folder if contain errors or warnings, repair this
2.) try comment import R in Activity file
// import com.mysite.packagename.R;
3.) every clean and rebuild project

Call requires API level 16 (current min is 4): android
Change The SDK version in AndroidManifest.xml to higher

<uses-sdk android:minSdkVersion="4" />
// 
<uses-sdk android:minSdkVersion="8" />