我实际上是在尝试创建一个链接到登录页面的android SQLite DB，这样我在oncreate方法期间在sqlite数据库中有一个条目，即admin和他的密码（前缀为“password”）。 但是，当我尝试使用ContentValues cv（我最初设置为null）...后跟cv.put ..我在onCreate上得到一个空指针异常（并不感到惊讶）。这是我这样做的正确方法吗？我想避免使用sql命令，因为我根本不熟悉它，但使用它作为最后的手段没有问题。 （这是代码 这是我用于创建数据库的DB2 Java类
public class DB2 {
//column details
public static final String KEY_ROWID = "_id";
public static final String KEY_NAME = "name";
public static final String KEY_NUMBER = "number";
public static final String KEY_EMAIL = "email";
public static final String KEY_PASSWORD = "password";
//db details
public static final String DATABASE_NAME = "Phonebook2DB";
public static final String DATABASE_TABLE = "contacts";
public static final int DATABASE_VERSION = 1;
private DBHelper ourHelper;
public final Context ourContext;
private static SQLiteDatabase ourDatabase;
//在probs的情况下检查我们的数据库var // test-ERROR可能在这里 static ContentValues cv;
private static class DBHelper extends SQLiteOpenHelper{
public DBHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
// TODO Auto-generated constructor stub
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
//Now we access the db and execute sql code
db.execSQL("CREATE TABLE " + DATABASE_TABLE + " (" + //sql commands have to be precise(note the spaces)
KEY_ROWID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +//NOW SEtup 1st col with ensuring the keyid be incremented
KEY_NAME + " TEXT NOT NULL, " + //2nd col all in blue are sql code
KEY_NUMBER +" TEXT NOT NULL, " +//3rd col
KEY_EMAIL + " TEXT NOT NULL, " +
KEY_PASSWORD + " TEXT NOT NULL);"
);
cv.put(KEY_NAME,"admin");
cv.put(KEY_NUMBER, "12345");
cv.put(KEY_EMAIL,"admin@admin.com");
cv.put(KEY_PASSWORD,"hello12345");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
db.execSQL("DROP TABLE IF EXISTS" + DATABASE_TABLE);
onCreate(db);
}
}
public DB2(Context c){
ourContext = c;
}
public DB2 open(){
ourHelper = new DBHelper(ourContext);
ourDatabase = ourHelper.getWritableDatabase();
return this;
}
public void close(){
ourHelper.close();
}
public long createEntry(String name,String number,String email,String password){
cv.put(KEY_NAME, name);
cv.put(KEY_NUMBER, number);
cv.put(KEY_EMAIL, email);
cv.put(KEY_PASSWORD, password);
return ourDatabase.insert(DATABASE_TABLE, null, cv);
}
public void deleteEntry(String name1){
ourDatabase.delete(DATABASE_TABLE, KEY_NAME + '=' + name1, null);
}
public String getdatabase(){
String columns[] = new String[]{KEY_ROWID,KEY_NAME,KEY_NUMBER,KEY_EMAIL,KEY_PASSWORD};
Cursor c = ourDatabase.query(DATABASE_TABLE, columns, null, null, null, null, null);
String output = "";
int iRowid = c.getColumnIndex(KEY_ROWID);
int iName = c.getColumnIndex(KEY_NAME);
int iNumber = c.getColumnIndex(KEY_NUMBER);
int iEmail = c.getColumnIndex(KEY_EMAIL);
for(c.moveToFirst();!c.isAfterLast();c.moveToNext())
output = output + " " + c.getString(iRowid) + "\t" + c.getString(iName) +"\t" + c.getString(iNumber) + "\t" + c.getString(iEmail) + "\n";
return output;
}
public String getPasswordByName(String lName){//getting password using from name for loginpage activity purposes
String columns[] = new String[]{KEY_ROWID,KEY_NAME,KEY_NUMBER,KEY_EMAIL,KEY_PASSWORD};
Cursor c = ourDatabase.query(DATABASE_TABLE, columns, KEY_NAME + '=' + lName, null, null, null,null);
if(c!=null){
c.moveToFirst();String Password = c.getString(4);return Password;
}
return null;
}
public String getName(String lName){//to check if login name exists??
String columns[] = new String[]{KEY_ROWID,KEY_NAME,KEY_NUMBER,KEY_EMAIL,KEY_PASSWORD};
Cursor c = ourDatabase.query(DATABASE_TABLE, columns, KEY_NAME + '=' + lName, null, null, null, null);
if(c!=null){
c.moveToFirst();String Name = c.getString(1);return Name;
}
return null;
}
}
这是我的LoginPage Java CLass的定义
public class LoginPage extends Activity implements OnClickListener{
Button login,forgotpass;
EditText user,pass;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.loginpage);
login = (Button) findViewById (R.id.BLogin);
forgotpass = (Button) findViewById (R.id.BForgotPass);
user = (EditText) findViewById (R.id.ETUsername);
pass = (EditText) findViewById (R.id.ETPasswd);
login.setOnClickListener(this);
forgotpass.setOnClickListener(this);
}
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
switch(arg0.getId()){
case R.id.BLogin:
String usernameinput = user.getText().toString();
String password = pass.getText().toString();
//now if usernameinput and password input match with entries in database then we r good to go
//long l = Long.parseLong(usernameinput);
DB2 dbname = new DB2(this);
dbname.open();
String returnedName;
returnedName = dbname.getName(usernameinput);
if(returnedName == "true" && password == dbname.getPasswordByName(usernameinput)){//here authenticating username and password
try{
Intent i = new Intent(LoginPage.this,MainStuff.class);
LoginPage.this.startActivity(i);
}catch(Exception e){e.printStackTrace();}
}
break;
case R.id.BForgotPass:
finish();//for now exit the function
break;
}
}
}
And here is the logcat
06-18 09:05:46.237: W/dalvikvm(802): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
06-18 09:05:46.247: E/AndroidRuntime(802): FATAL EXCEPTION: main
06-18 09:05:46.247: E/AndroidRuntime(802): java.lang.NullPointerException
06-18 09:05:46.247: E/AndroidRuntime(802): at com.example.phonebook2.DB2$DBHelper.onCreate(DB2.java:49)
06-18 09:05:46.247: E/AndroidRuntime(802): at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:252)
06-18 09:05:46.247: E/AndroidRuntime(802): at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164)
06-18 09:05:46.247: E/AndroidRuntime(802): at com.example.phonebook2.DB2.open(DB2.java:71)
06-18 09:05:46.247: E/AndroidRuntime(802): at com.example.phonebook2.LoginPage.onClick(LoginPage.java:39)
06-18 09:05:46.247: E/AndroidRuntime(802): at android.view.View.performClick(View.java:4204)
06-18 09:05:46.247: E/AndroidRuntime(802): at android.view.View$PerformClick.run(View.java:17355)
06-18 09:05:46.247: E/AndroidRuntime(802): at android.os.Handler.handleCallback(Handler.java:725)
06-18 09:05:46.247: E/AndroidRuntime(802): at android.os.Handler.dispatchMessage(Handler.java:92)
06-18 09:05:46.247: E/AndroidRuntime(802): at android.os.Looper.loop(Looper.java:137)
06-18 09:05:46.247: E/AndroidRuntime(802): at android.app.ActivityThread.main(ActivityThread.java:5041)
06-18 09:05:46.247: E/AndroidRuntime(802): at java.lang.reflect.Method.invokeNative(Native Method)
06-18 09:05:46.247: E/AndroidRuntime(802): at java.lang.reflect.Method.invoke(Method.java:511)
06-18 09:05:46.247: E/AndroidRuntime(802): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
06-18 09:05:46.247: E/AndroidRuntime(802): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
06-18 09:05:46.247: E/AndroidRuntime(802): at dalvik.system.NativeStart.main(Native Method)
我是Android的初学者，所以请随时提出改进我的代码的方法。 感谢
答案 0 :(得分：0)
在创建数据库期间触发DBHelper.onCreate()方法时，变量cv不存在。要填充主数据，您可以使用简单的插入语句。
替换
cv.put(KEY_NAME,"admin");
cv.put(KEY_NUMBER, "12345");
cv.put(KEY_EMAIL,"admin@admin.com");
cv.put(KEY_PASSWORD,"hello12345");
使用简单的插入语句
string sql = "INSERT INTO " + DATABASE_TABLE + "(" + KEY_NAME + ", " + KEY_NUMBER + ", " + KEY_EMAIL + ", " + KEY_PASSWORD + ") VALUES('admin', '12345', 'admin@admin.com', 'hello12345');";
db.execSQL(sql);
答案 1 :(得分：0)
在您的课程DBHelper，public long createEntry()方法，
只需在顶部添加此行
即可 ContentValues cv = new ContentValues();