当我点击我的应用程序第一个按钮时，它停止工作 亲切的建议，可能是什么问题？
在我的代码中，我试图打开一个布局，当它点击按钮然后打开另一个布局，然后当点击它的按钮然后将数据保存在数据库中。
我的loginActivity代码是 - 包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;
}
}
}
它在logcat上给出了这个错误
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)