我收到此错误：
05-09 23:34:04.251 21214-21214/com.example.averm.phonecontact E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.averm.phonecontact, PID: 21214
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.averm.phonecontact/com.example.averm.phonecontact.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'int com.example.averm.phonecontact.DatabaseHandler.getContactsCount()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2335)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2397)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1310)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5268)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:902)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:697)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int com.example.averm.phonecontact.DatabaseHandler.getContactsCount()' on a null object reference
at com.example.averm.phonecontact.MainActivity.onCreate(MainActivity.java:106)
at android.app.Activity.performCreate(Activity.java:6033)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2288)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2397)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1310)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5268)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:902)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:697)
我的代码是：
MainActivity.java类：
public class MainActivity extends AppCompatActivity {
private EditText nameTxt, phoneTxt, emailTxt, addressTxt;
ImageView contactImageImgView;
List<Contact> Contacts = new ArrayList<Contact>();
ListView contactListView;
Uri imageUri = Uri.parse("android.resource://org.intracode.contactmanager/drawable/no_user_logo.png");
DatabaseHandler dbHandler;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
nameTxt = (EditText)findViewById(R.id.edName);
phoneTxt = (EditText)findViewById(R.id.edNumber);
emailTxt = (EditText)findViewById(R.id.edEmail);
addressTxt = (EditText)findViewById(R.id.edAddress);
contactListView = (ListView)findViewById(R.id.listView);
contactImageImgView = (ImageView)findViewById(R.id.imgViewContactImage);
TabHost tabHost = (TabHost)findViewById(R.id.tabHost);
tabHost.setup();
TabHost.TabSpec tabSpec = tabHost.newTabSpec("creator");
tabSpec.setContent(R.id.tabCreator);
tabSpec.setIndicator("Creator");
tabHost.addTab(tabSpec);
tabSpec = tabHost.newTabSpec("List");
tabSpec.setContent(R.id.tabContactList);
tabSpec.setIndicator("List");
tabHost.addTab(tabSpec);
final Button addBtn = (Button)findViewById(R.id.btnAdd);
addBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Contact contact = new Contact(dbHandler.getContactsCount(), String.valueOf(nameTxt.getText()), String.valueOf(phoneTxt.getText()),
String.valueOf(emailTxt.getText()), String.valueOf(addressTxt.getText()), imageUri);
if (!contactExists(contact)){
dbHandler.createContact(contact);
Contacts.add(contact);
Toast.makeText(getApplicationContext(),String.valueOf(nameTxt.getText()) +" has been added to your Contacts!", Toast.LENGTH_SHORT).show();
return;
}
Toast.makeText(getApplicationContext(), String.valueOf(nameTxt.getText()) + " already exists. Please use a different name.", Toast.LENGTH_SHORT).show();
}
});
nameTxt.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(nameTxt.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.getContactsCount() != 0)
Contacts.addAll(dbHandler.getAllContacts());
populateList();
}
public void onActivityResult(int reqCode, int resCode, Intent data){
if (resCode == RESULT_OK){
if (reqCode == 1){
imageUri = data.getData();
contactImageImgView.setImageURI(imageUri);
}
}
}
private boolean contactExists(Contact contact) {
String name = contact.getName();
int contactCount = Contacts.size();
for (int i = 0; i < contactCount; i++) {
if (name.compareToIgnoreCase(Contacts.get(i).getName()) == 0)
return true;
}
return false;
}
private void populateList(){
ArrayAdapter<Contact> adaptor= new ContactListAdaptor();
contactListView.setAdapter(adaptor);
}
private class ContactListAdaptor extends ArrayAdapter<Contact>{
public ContactListAdaptor(){
super(MainActivity.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 name = (TextView) view.findViewById(R.id.contactName);
name.setText(currentContact.getName());
TextView phone = (TextView) view.findViewById(R.id.phoneNumber);
phone.setText(currentContact.getPhone());
TextView email = (TextView) view.findViewById(R.id.emailAddress);
email.setText(currentContact.getEmail());
TextView address = (TextView) view.findViewById(R.id.cAddress);
address.setText(currentContact.getAddress());
ImageView ivContactImage = (ImageView) view.findViewById(R.id.ivContactImage);
ivContactImage.setImageURI(currentContact.getImageURI());
return view;
}
}
}
DatabaseHandler.java类：
public class DatabaseHandler extends SQLiteOpenHelper {
private static final int DATABASE_VERSION = 2;
private static final String DATABASE_NAME = "contactManager",
TABLE_CONTACTS = "contacts",
KEY_ID = "id",
KEY_NAME = "name",
KEY_PHONE = "phone",
KEY_EMAIL = "email",
KEY_ADDRESS = "address",
KEY_IMAGEURI = "imageUri";
public DatabaseHandler(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("CREATE TABLE " + TABLE_CONTACTS + "(" + KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT," + KEY_NAME + " TEXT," + KEY_PHONE + " TEXT," + KEY_EMAIL + " TEXT," + KEY_ADDRESS + " TEXT," + KEY_IMAGEURI + " TEXT)");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS " + TABLE_CONTACTS);
onCreate(db);
}
public void createContact(Contact contact) {
SQLiteDatabase db = getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_NAME, contact.getName());
values.put(KEY_PHONE, contact.getPhone());
values.put(KEY_EMAIL, contact.getEmail());
values.put(KEY_ADDRESS, contact.getAddress());
values.put(KEY_IMAGEURI, contact.getImageURI().toString());
db.insert(TABLE_CONTACTS, null, values);
db.close();
}
public Contact getContact(int id) {
SQLiteDatabase db = getReadableDatabase();
Cursor cursor = db.query(TABLE_CONTACTS, new String[] { KEY_ID, KEY_NAME, KEY_PHONE, KEY_EMAIL, KEY_ADDRESS, KEY_IMAGEURI }, KEY_ID + "=?", new String[] { String.valueOf(id) }, null, null, null, null );
if (cursor != null)
cursor.moveToFirst();
Contact contact = new Contact(Integer.parseInt(cursor.getString(0)), cursor.getString(1), cursor.getString(2), cursor.getString(3), cursor.getString(4), Uri.parse(cursor.getString(5)));
db.close();
cursor.close();
return contact;
}
public int getContactsCount() {
SQLiteDatabase db = getReadableDatabase();
Cursor cursor = db.rawQuery("SELECT * FROM " + TABLE_CONTACTS, null);
int count = cursor.getCount();
db.close();
cursor.close();
return count;
}
}
答案 0 :(得分：0)
您有一个dbHandler字段。您永远不会在dbHandler=new DatabaseHandler(this)中致电onCreate()，因此dbHandler为null。
另外，请在后台线程上进行数据库I / O.
答案 1 :(得分：0)
您已经创建了DatabaseHandler实例，但从未使用任何值对其进行初始化。您必须创建类的对象，然后使用它来访问方法。在onCreate of your activity中添加以下代码
DatabaseHandler dbHandler=new DatabaseHandler(this)