我正在创建一个Android应用程序，它包含使用sqllite的注册表单。当我单击注册按钮时，它显示 java.lang.NullPointerException 。任何人都可以告诉我我在哪里犯了错误。我正在尝试这个1小时，这太烦人了，请帮助我。
这是我的活动：
registration = (ButtonFloatSmall)findViewById(R.id.btn_flt_sml_registration);
registration.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
registrationdialog = new Dialog(Login.this); //Creating a dialog
registrationdialog.setContentView(R.layout.registrationdialog); //Adding custom layout to a dialog
registrationdialog.setTitle("User Registration"); //Setting title to a dialog
registrationdialog.setCancelable(false);
username_dialog = (EditText)registrationdialog.findViewById(R.id.edt_dialog_username);
password_dialog = (EditText)registrationdialog.findViewById(R.id.edt_dialog_password);
confirm_password = (EditText)registrationdialog.findViewById(R.id.edt_dialog_confirm_password);
/*------For viewing passwords if "Show passwords" is checked---*/
show_password =(CheckBox)registrationdialog.findViewById(R.id.show_password);
show_password.setOnCheckedChangeListener(new OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
if(!isChecked){
password_dialog.setTransformationMethod(PasswordTransformationMethod.getInstance());
confirm_password.setTransformationMethod(PasswordTransformationMethod.getInstance());
}
else{
password_dialog.setTransformationMethod(HideReturnsTransformationMethod.getInstance());
confirm_password.setTransformationMethod(HideReturnsTransformationMethod.getInstance());
}
}
});
Registerbutton = (Button)registrationdialog.findViewById(R.id.Btn_Register);
Registerbutton.setMode(ActionProcessButton.Mode.ENDLESS);
Registerbutton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
username_dialog_string = username_dialog.getText().toString();
password_dialog_string = password_dialog.getText().toString();
confirm_password_string = confirm_password.getText().toString();
if(username_dialog_string.equals("")||password_dialog_string.equals("")||confirm_password_string.equals("")){
validation_manager.validateAllAndSetError();
}
else if(password_dialog_string.equals(confirm_password_string)){
progressGenerator.start(Registerbutton);
logindatabaseadapter.insertEntry(username_dialog_string,password_dialog_string);
Registerbutton.setEnabled(false);
username_dialog.setEnabled(false);
password_dialog.setEnabled(false);
confirm_password.setEnabled(false);
registrationdialog.setCancelable(true);
}
else{
Toast.makeText(Login.this, "Password and confirm passwords are not matched please try again ", Toast.LENGTH_LONG).show();
}
}
});
clear_Button = (ActionProcessButton)registrationdialog.findViewById(R.id.Btn_Clear);
clear_Button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
username_dialog.setText("");
password_dialog.setText("");
confirm_password.setText("");
}
});
registrationdialog.show();
}
});
这是我的登录数据库适配器：
package com.developer.milanandroid;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
public class LoginDataBaseAdapter
{
static final String DATABASE_NAME = "MilanloginRegistration.db";
static final int DATABASE_VERSION = 1;
public static final int NAME_COLUMN = 1;
// TODO: Create public field for each column in your table.
// SQL Statement to create a new database.
static final String DATABASE_CREATE = "create table "+"MilanLoginregistration"+
"( " +"ID"+" integer primary key autoincrement,"+"USERNAME text UNIQUE,PASSWORD text); ";
// Variable to hold the database instance
public SQLiteDatabase db;
// Context of the application using the database.
private final Context context;
// Database open/upgrade helper
private DataBaseHelper dbHelper;
public LoginDataBaseAdapter(Context _context)
{
context = _context;
dbHelper = new DataBaseHelper(context, DATABASE_NAME, null, DATABASE_VERSION);
}
public LoginDataBaseAdapter open() throws SQLException
{
db = dbHelper.getWritableDatabase();
return this;
}
public void close()
{
db.close();
}
public SQLiteDatabase getDatabaseInstance()
{
return db;
}
public void insertEntry(String username,String password)
{
ContentValues newValues = new ContentValues();
newValues.put("USERNAME",username);
newValues.put("PASSWORD",password);
// Insert the row into your table
db.insert("MilanLoginregistration",null,newValues);
///Toast.makeText(context, "Reminder Is Successfully Saved", Toast.LENGTH_LONG).show();
}
public int deleteEntry(String username,String password)
{
//String id=String.valueOf(ID);
String where="USERNAME=?";
int numberOFEntriesDeleted= db.delete("MilanLoginregistration", where, new String[]{username,password}) ;
// Toast.makeText(context, "Number fo Entry Deleted Successfully : "+numberOFEntriesDeleted, Toast.LENGTH_LONG).show();
return numberOFEntriesDeleted;
}
public String getSinlgeEntry(String userName)
{
Cursor cursor=db.query("MilanLoginregistration", null, " USERNAME=?", new String[]{userName}, null, null, null);
if(cursor.getCount()<1) // UserName Not Exist
{
cursor.close();
return "NOT EXIST";
}
cursor.moveToFirst();
String password= cursor.getString(cursor.getColumnIndex("PASSWORD"));
cursor.close();
return password;
}
public void updateEntry(String user_name,String pasword)
{
// Define the updated row content.
ContentValues updatedValues = new ContentValues();
// Assign values for each row.
updatedValues.put("USERNAME", user_name);
updatedValues.put("PASSWORD",pasword);
String where="USERNAME = ?";
db.update("MilanLoginregistration",updatedValues, where, new String[]{user_name});
}
}
这是我的logcat：
04-16 19:32:56.962: E/AndroidRuntime(6545): FATAL EXCEPTION: main
04-16 19:32:56.962: E/AndroidRuntime(6545): Process: com.developer.milanandroid, PID: 6545
04-16 19:32:56.962: E/AndroidRuntime(6545): java.lang.NullPointerException
04-16 19:32:56.962: E/AndroidRuntime(6545): at com.developer.milanandroid.Login$1$2.onClick(Login.java:181)
04-16 19:32:56.962: E/AndroidRuntime(6545): at android.view.View.performClick(View.java:4463)
04-16 19:32:56.962: E/AndroidRuntime(6545): at android.view.View$PerformClick.run(View.java:18770)
04-16 19:32:56.962: E/AndroidRuntime(6545): at android.os.Handler.handleCallback(Handler.java:808)
04-16 19:32:56.962: E/AndroidRuntime(6545): at android.os.Handler.dispatchMessage(Handler.java:103)
04-16 19:32:56.962: E/AndroidRuntime(6545): at android.os.Looper.loop(Looper.java:193)
04-16 19:32:56.962: E/AndroidRuntime(6545): at android.app.ActivityThread.main(ActivityThread.java:5292)
04-16 19:32:56.962: E/AndroidRuntime(6545): at java.lang.reflect.Method.invokeNative(Native Method)
04-16 19:32:56.962: E/AndroidRuntime(6545): at java.lang.reflect.Method.invoke(Method.java:515)
04-16 19:32:56.962: E/AndroidRuntime(6545): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:824)
04-16 19:32:56.962: E/AndroidRuntime(6545): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:640)
04-16 19:32:56.962: E/AndroidRuntime(6545): at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：1)
尝试在调用任何查询之前初始化db类，然后在调用每个查询之前打开数据库，然后在查询后关闭它。
LoginDataBaseAdapter logindatabaseadapter; (Global)
logindatabaseadapter = new LoginDataBaseAdapter (this);
logindatabaseadapter.open();
logindatabaseadapter.insertEntry(username_dialog_string,password_dialog_string);
logindatabaseadapter.close();