android - linearLayout not included in R java file -

so following tutorial found here: developer site.

my code looks below:

import android.os.bundle; import android.app.activity; import android.widget.linearlayout;  import com.google.android.gms.ads.adrequest; import com.google.android.gms.ads.adsize; import com.google.android.gms.ads.adview;  // simple {@link activity} embeds adview. public class mainactivity extends activity {   // view show ad.   private adview adview;    // ad unit id. replace actual ad unit id.   private static final string ad_unit_id = "insert_your_ad_unit_id_here";    // called when activity first created.   @override   public void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);      // create ad.     adview = new adview(this);     adview.setadsize(adsize.banner);     adview.setadunitid(ad_unit_id);      // add adview view hierarchy. view have no size     // until ad loaded.     linearlayout layout = (linearlayout) findviewbyid(r.id.linearlayout);     layout.addview(adview);      // create ad request. check logcat output hashed device id     // test ads on physical device.     adrequest adrequest = new adrequest.builder()         .addtestdevice(adrequest.device_id_emulator)         .addtestdevice("insert_your_hashed_device_id_here")         .build();      // start loading ad in background.     adview.loadad(adrequest);   }    @override   public void onresume() {     super.onresume();     if (adview != null) {       adview.resume();     }   }    @override   public void onpause() {     if (adview != null) {       adview.pause();     }     super.onpause();   }    // called before activity destroyed.   @override   public void ondestroy() {     // destroy adview.     if (adview != null) {       adview.destroy();     }     super.ondestroy();   } } 

however, getting single unresolved error keeping me testing app. on line

linearlayout layout = (linearlayout) findviewbyid(r.id.linearlayout); 

i getting error linearlayout being unresolved. r , r.id fine. when r.java sure enough there no linearlayout. don't want put in there, since r.java generated.

i'm still new android development, , don't know how resolve issue. how make things included in r.java? i've tried editing files such activity_main.xml include linearlayout, when , try run app "installation error: unknown error. please check logcat more details.". don't know logcat trying tell me when @ it. have "import android.widget.linearlayout". don't know / i'm doing wrong.

you job solving problem. such as

1)may not identify id linearlayout of linearlayout 2)import linearlayout class 3)you clean project. 4)you delete bin , gen folder