我正在创建一个登录页面，该页面将使用 e sqlite db 进行身份验证。当我将数据输入到我编辑文本字段并单击“登录”时，应将文本字段中的数据与 sqlite db 中的数据进行比较。出于某种原因，我得到了我的捕获异常错误“null”。我相信我的查询没有提取需要比较的数据。当我的程序运行时，除了捕获异常之外，我没有收到任何错误......令人沮丧！
我的 OnClick 方法比较和登录：
lsLogin.setOnClickListener (new OnClickListener() {
@Override
public void onClick(View v) {
//check login
String username = lsUsername.getText().toString();
String password = lsPassword.getText().toString();
try{
if(LoginDB.Login(username,password)) {
Intent goToNextActivity = new Intent(getApplicationContext(), menu.class);
startActivity(goToNextActivity);
Toast.makeText(LoginScrExample.this,"Login Sucessful",Toast.LENGTH_LONG).show();
}else{
Toast.makeText(LoginScrExample.this,"Invalid Username/Password",Toast.LENGTH_LONG).show();
}
}
catch(Exception err)
{
Toast.makeText(LoginScrExample.this," Something is wrong " + err.getMessage(),Toast.LENGTH_LONG).show();
}
我的数据库类：
public LoginDB(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
String sqlDataStore = "create table if not exists " +
TABLE_NAME_CREDENTIALS + " ("+ BaseColumns._ID + " integer primary key autoincrement,"
+ COLUMN_NAME_USERNAME + " text not null,"
+ COLUMN_NAME_PASSWORD + " text not null);";
db.execSQL(sqlDataStore);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
if(oldVersion == 1 && newVersion == 2){
//Upgrade the database
}
}
public static boolean Login(String username, String password) {
Cursor c = DBHelper.getReadableDatabase().rawQuery(
"SELECT * FROM " + TABLE_NAME_CREDENTIALS + " WHERE "
+ COLUMN_NAME_USERNAME + "='" + username +"'AND "+COLUMN_NAME_PASSWORD+"='"+ password +"'" , null);
if (c.getCount()>0)
return true;
return false;
}
public void open() {
// TODO Auto-generated method stub
db = DBHelper.getWritableDatabase();
}
public void close() {
DBHelper.close();
}
我也尝试了这个查询，但得到了相同的结果：
public static boolean Login(String username, String password) throws SQLException
{
Cursor mCursor = db.rawQuery("SELECT * FROM " + TABLE_NAME_CREDENTIALS + " WHERE username=? AND password=?",
new String[]{username,password});
if(mCursor !=null) {
if(mCursor.getCount()>0)
{
return true;
}
}
return false;
}
错误日志：
08-23 13:38:24.034: W/System.err(1027): java.lang.NullPointerException
08-23 13:38:24.034: W/System.err(1027): at com.LoginScr.Example.LoginDB.Login(LoginDB.java:58)
08-23 13:38:24.043: W/System.err(1027): at com.LoginScr.Example.LoginScrExample$1.onClick(LoginScrExample.java:50)
08-23 13:38:24.043: W/System.err(1027): at android.view.View.performClick(View.java:3511)
08-23 13:38:24.043: W/System.err(1027): at android.view.View$PerformClick.run(View.java:14105)
08-23 13:38:24.054: W/System.err(1027): at android.os.Handler.handleCallback(Handler.java:605)
08-23 13:38:24.054: W/System.err(1027): at android.os.Handler.dispatchMessage(Handler.java:92)
08-23 13:38:24.054: W/System.err(1027): at android.os.Looper.loop(Looper.java:137)
08-23 13:38:24.054: W/System.err(1027): at android.app.ActivityThread.main(ActivityThread.java:4424)
08-23 13:38:24.083: W/System.err(1027): at java.lang.reflect.Method.invokeNative(Native Method)
08-23 13:38:24.083: W/System.err(1027): at java.lang.reflect.Method.invoke(Method.java:511)
08-23 13:38:24.094: W/System.err(1027): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
08-23 13:38:24.094: W/System.err(1027): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
08-23 13:38:24.094: W/System.err(1027): at dalvik.system.NativeStart.main(Native Method)