unfortunately your app has stopped working when I click on button - runtime

Question

When I click on my app first button it stopped working
kindly advice,what can be the issue?
In my code,I am trying to open one layout when it button is click then is open another layout and then when its button is being clicked then is save data in database.
My loginActivity code is -
package com.example.ahmed.vehiclepermitapp;
import android.app.Activity;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.ContextMenu;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TabHost;
import android.widget.TextView;
import android.widget.Toast;
import java.util.ArrayList;
import java.util.List;
public class LoginActivity extends Activity {
private static final int EDIT=0, DELETE=1;
EditText carTxt, statusTxt;
ImageView contactImageImgView;
List<Contact> Contacts = new ArrayList<Contact>();
ListView contactListView;
Uri imageUri=Uri.parse("android.resource://com.newthinktank.helloworld/drawable/search.png");
DatabaseHandler dbHandler;
int longClickItemIndex;
ArrayAdapter<Contact> contactAdapter;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.login);
final Button loginBtn = (Button) findViewById(R.id.btnLogin);
loginBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
setContentView(R.layout.activity_main);
carTxt = (EditText) findViewById(R.id.txtCar);
statusTxt = (EditText) findViewById(R.id.txtStatus);
contactListView = (ListView) findViewById(R.id.listView);
contactImageImgView = (ImageView) findViewById(R.id.imgViewContactImage);
dbHandler = new DatabaseHandler(getApplicationContext());
registerForContextMenu(contactListView);
contactListView.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
#Override
public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id) {
longClickItemIndex = position;
return false;
}
});
TabHost tabHost = (TabHost) findViewById(R.id.tabHost);
tabHost.setup();
TabHost.TabSpec tabSpec = tabHost.newTabSpec("Creator");
tabSpec.setContent(R.id.Creator);
tabSpec.setIndicator("Creator");
tabHost.addTab(tabSpec);
tabSpec = tabHost.newTabSpec("List");
tabSpec.setContent(R.id.List);
tabSpec.setIndicator("List");
tabHost.addTab(tabSpec);
final Button addBtn = (Button) findViewById(R.id.btnLogin);
addBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Contact contact = new Contact(dbHandler.getContactCount(), String.valueOf(carTxt.getText()), String.valueOf(statusTxt.getText()), imageUri);
if (!contactExists(contact)) {
dbHandler.createContact(contact);
Contacts.add(contact);
contactAdapter.notifyDataSetChanged();
Toast.makeText(getApplicationContext(), String.valueOf(carTxt.getText()) + " has been add to list", Toast.LENGTH_SHORT).show();
return;
}
Toast.makeText(getApplicationContext(), String.valueOf(carTxt.getText()) + "already exists. please use different name", Toast.LENGTH_SHORT).show();
}
});
carTxt.addTextChangedListener(new TextWatcher() {
#Override
public void beforeTextChanged(CharSequence s, int start, int count, int after) {
}
#Override
public void onTextChanged(CharSequence s, int start, int before, int count) {
addBtn.setEnabled(String.valueOf(carTxt.getText()).trim().length() > 0);
}
#Override
public void afterTextChanged(Editable s) {
}
});
contactImageImgView.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent();
intent.setType("image/*");
intent.setAction(Intent.ACTION_GET_CONTENT);
startActivityForResult(Intent.createChooser(intent, "Select Contact Image"), 1);
}
});
if (dbHandler.getContactCount() != 0)
Contacts.addAll(dbHandler.getAllContacts());
populateList();
}
});}
public void onCreateContextMenu(ContextMenu menu,View view,ContextMenu.ContextMenuInfo menuInfo){
super.onCreateContextMenu(menu,view,menuInfo);
menu.setHeaderIcon(R.drawable.pencil_con);
menu.setHeaderTitle("Option");
menu.add(Menu.NONE,EDIT,menu.NONE,"Edit Option");
menu.add(Menu.NONE,DELETE,menu.NONE,"Delete Option");
}
public boolean onContextItemSelected(MenuItem item){
switch (item.getItemId()){
case EDIT:
dbHandler.updateContact(Contacts.get(longClickItemIndex));
contactAdapter.notifyDataSetChanged();
break;
case DELETE:
dbHandler.deleteContact(Contacts.get(longClickItemIndex));
Contacts.remove(longClickItemIndex);
contactAdapter.notifyDataSetChanged();
break;
}
return super.onContextItemSelected(item);
}
private boolean contactExists(Contact contact){
String name = contact.getCar();
int countactCount = Contacts.size();
for (int i = 0; i < countactCount; i++)
{
if (name.compareToIgnoreCase(Contacts.get(i).getCar()) == 0)
return true;
}
return false;
}
public void onActivityResult(int reqcode, int rescode, Intent data){
if(rescode == RESULT_OK){
if(reqcode == 1){
imageUri = data.getData();
contactImageImgView.setImageURI(data.getData());
}
}
}
private void populateList() {
contactAdapter = new ContactListAdapter();
contactListView.setAdapter(contactAdapter);
}
class ContactListAdapter extends ArrayAdapter<Contact> {
public ContactListAdapter() {
super(LoginActivity.this, R.layout.listview_item, Contacts);
}
#Override
public View getView(int position, View view, ViewGroup parent) {
if (view == null)
view = getLayoutInflater().inflate(R.layout.listview_item, parent, false);
Contact currentContact = Contacts.get(position);
TextView car = (TextView) view.findViewById(R.id.contactname);
car.setText(currentContact.getCar());
TextView status = (TextView) view.findViewById(R.id.status);
status.setText(currentContact.getStatus());
ImageView img = (ImageView) view.findViewById(R.id.img);
img.setImageURI(currentContact.getimageURI());
return view;
}
}
}
it give this error on logcat
09-06 05:05:16.954
4910-4910/com.example.ahmed.vehiclepermitapp E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.NullPointerException
at com.example.ahmed.vehiclepermitapp.LoginActivity$1.onClick(LoginActivity.java:85)
at android.view.View.performClick(View.java:4106)
at android.view.View$PerformClick.run(View.java:17052)
at android.os.Handler.handleCallback(Handler.java:615)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5059)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:792)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:555)
at dalvik.system.NativeStart.main(Native Method)