Rename Android project package issue in Eclipse - R cannot be resolved to a variable

GregorianCalendar cal = new GregorianCalendar(); Boolean b = cal.isLeapYear(2012); // true, Android example.

public class MainActivity extends Activity {
TextView txtV;
	Context cntx;
	
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        txtV = (TextView)findViewById(R.id.idLabel);
        cntx = this;
        StringBuilder strBuild = new StringBuilder();
        
         GregorianCalendar cal = new GregorianCalendar();
         Boolean b = cal.isLeapYear(2012); // true
         strBuild.append("Is leap year 2012? " + b + "

");
         b = cal.isLeapYear(2014);         // false
         strBuild.append("Is leap year 2014? " + b + "

");
         
         
         txtV.setText(strBuild);
    }
}

Chytré telefony s Androidem - tabulka srovnání dle ceny:

Výrobce	Model (codename)	Cena, včetně DPH	CPU MHz	displej-rozlišení	Velikost displeje v palcích	ROM	RAM
Huawei	Vodafone 845 (U8120, Joy)	1979	528	240x320	2.8	512	256
ZTE	Vodafone 945 (ZTE Joe)	1999	600	240x400	3.2	512	512
Huawei	Vodafone 858 Smart (U8160)	2177	528	240x320	2.8	512	256
Alcatel	T-Mobile Move (OT 908)	2294	600	240x320	2.8	512	512
Samsung	Galaxy Y (S5360)	2495	832	240x320	3	512	256
ZTE	Racer II (Arizona)	2536	500	240x320	2.8	512	256
Huawei	Ideos X1 (U8180, Orange Stockholm)	2549	528	240x320	2.8	512	256
Huawei	U8100	2595	528	240x320	2.8	512	256
Huawei	U8500	2699	600	320x480	3.2	512	256
Samsung	Galaxy Mini (S5570)	2799	600	240x320	3.14	512	256
Samsung	Galaxy 5, 550 (i5500)	2855	600	240x320	2.8	512	256
LG	Optimus Me (P350)	2924	600	240x320	2.8	512	512
SE	Xperia X8	2977	600	320x480	3	512	256
Gigabyte	GSmart G1310 (Roy)	2990	528	320x480	3.2	512	256
MyPhone	A210	2990	624	240x400	3	256	128
ZTE	Orange San Francisco (ZTE Blade, U880, P729V)	2999	600	480x800	3.5	512	512
HTC	Explorer (Pico)	3104	600	320x480	3.2	512	512
Huawei	U8650 (Sonic)	3290	600	320x480	3.5	512	256
Huawei	Ideos X3 (U8510, Blaze)	3377	600	320x480	3.2	512	256
Samsung	Galaxy Y Pro (B5510)	3390	832	240x320	2.6
Gigabyte	GSmart G1317D (Rola)	3504	528	240x400	3.2	512	256
SE	Xperia Live Walkman (WT19i)	3554	1000	320x480	3.2	1024	512
Huawei	T-Mobile Comet (Ideos, U8150)	3600	528	240x320	2.8	512	256
SE	Xperia X10 mini pro (U20i, Mimmi)	3777	600	240x320	2.55	512	256
LG	Optimus Swift (GT540)	3800	600	320x480	3	512	256
SE	Xperia Mini (ST15)	3800	1000	320x480	3	1024	512
LG	Optimus One (P500)	3919	600	320x480	3.2	512	512
LG	Optimus Pro	3928	800	240x320	2.8	512	256
HTC	Wildfire (Buzz, Mocha, A3333)	3999	528	240x320	3.2	512	384
LG	Optimus Net (P690)	4108	800	320x480	3.2	512	512
Samsung	Galaxy Gio (S5660)	4185	800	320x480	3.2	512	384
LG	Optimus Hub (Univa)	4195	800	320x480	3.5	512	512
SE	Xperia  X10 mini (E10i, Robyn)	4195	600	240x320	2.55	512	256
Samsung	Galaxy 3, 580, Taos (i5800)	4500	667	240x400	3.2	512	256
Samsung	Galaxy Ace+ (S7500)	4550	1000	320x480	3.65	4096	512
LG	Optimus Chic (E720)	4550	600	320x480	3.2	512	512
Samsung	Galaxy 551 (i5510)	4577	667	240x400	3.2	512	512
Motrolola	Liquid Mini E310	4600	600	320x480	3.2	512	512
HTC	Wildfire S (Marvell)	4777	600	320x480	3.2	512	512
Verzo	Kinzo	4799	1000	480x800	4.3	512	512
Samsung	Galaxy Ace (S5830)	4800	800	320x480	3.5	512	256
Motorola	Defy mini	4800	600	320x480	3.2	512	512
Samsung	Galaxy Spica, Portal, Lite (i5700)	4800	800	320x480	3.2	512	256
HTC	Gratia (A6380, Liberty, Aria)	4937	480	320x480	3.2	512	384
SE	Xperia mini pro (SK17i, Mango)	4944	1000	320x480	3	1024	320
Huawei	Ideos X5 (U8800)	4977	800	480x800	3.8	4096	512
HTC	Salsa (C510e)	4990	600	320x480	3.4	576	512
Huawei	Boulder	4998	528	240x320	2.6	512	256
ZTE	Orange Monte Carlo (ZTE Skate)	5177	800	480x800	4.3	512	512
Samsung	Galaxy S (i9000)	5300	1000	480x800	4	15600	512
Gigabyte	GSmart G1315	5490	528	320x480	3.5	512	256
SE	Xperia Active	5500	1000	320x480	3	1024	512
Samsung	Google Nexus One	5750	1000	480x800	3.7	512	512
HTC	Desire  (A8181, Bravo)	5999	1000	480x800	3.7	576	512
LG	Optimus Black (P970)	6000	1000	480x800	4	1908	512
SE	Xperia Play	6000	1000	480x854	4
LG	Optimus Sol (Victor, E730)	6000	1000	480x800	3.8	2048	512
Acer	Liquid Metal S120	6061	800	480x800	3.6	512	512
Samsung	Google Nexus S	6200	1000	480x800	4	15600	512
HTC	Desire Z (A7272, Vision)	6200	800	480x800	3.7	1536	512
Samsung	Galaxy W (i8150, Ancora)	6200	1400	480x800	3.7	4096	512
SE	Xperia Ray (ST18i)	6344	1000	480x854	3.3	1024	512
Motorola	Defy (MB525, Jordan)	6377	800	480x854	3.7	1908	512
Motorola	Defy + (MB526)	6377	1000	480x854	3.7	1908	512
Samsung	Galaxy XCover (S5690)	6399	800	320x480	3.65	512	512
Gigabyte	GSmart G1345	6490	800	320x480	3.5	512	512
HTC	Evo 3D	6500	1200	540x960	4.3	1024	1024
HTC	Desire HD (Ace)	6500	1000	480x800	4.3	1900	768
Huawei	Honour (U8660)	6500	1400	480x854	4	4096	512
SE	Xperia Neo	6590	1000	480x854	3.7	1024	512
HTC	Legend (A6363)	6784	600	320x480	3.2	512	384
Huawei	Vision (U8850)	6999	1000	480x800	3.7	2048	512
SE	Xperia Arc (LT15i)	7390	1000	480x854	4.2	1024	512
SE	Xperia Pro (MK16i)	7890	1000	480x854	3.7	1024	512
HTC	Hero	7975	528	320x480	3.2	288	512
SE	Xperia Arc S (LT18i)	8590	1400	480x854	4.2	1024	512
Samsung	Xperia Live Walkman (WT19i)	9700	1500	480x800	4.3	16000	1024
Motorola	Droid Razr	11800	1200	540x960	4.3	15600	1024

Where file(s) does eclipse store Java code style settings to?
If you need copy any old templates to the new workspace.

workspace\.metadata\.plugins\org.eclipse.core.runtime\.settings\org.eclipse.jdt.ui.prefs

You can edit the Eclipse Templates from menu Window - Preferences - Java - Editor - Templates.

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

How install Android emulator on PC
//developer.android.com/sdk/installing.html

Download links:
Java Development Kit JDK download
Eclipse download
Android SDK download