android - 匹配用户名和密码时出现空异常

Question

我正在创建一个基于登录 Activity 的应用程序。当我进行注册(注册)时，所有数据都已成功进入数据库，但是当用户处于登录 Activity 并尝试登录时，在异常中出现空值。

这是我的代码，

        loginuserid=etloginuserid.getText().toString();
        loginpassword=etloginpassword.getText().toString();
        try
        {
            String storedPassword=db.getPasswordOfThisUser(loginuserid);

            if(loginpassword.equals(storedPassword))
            {
                Toast.makeText(getApplicationContext(), "Login Successfull", Toast.LENGTH_SHORT).show();
                Intent iwelpage=new Intent(this,WelcomeActivity.class);
                startActivity(iwelpage);
                finish();
                break;
            }
            else
            {
                Toast.makeText(getApplicationContext(), "Username or Password does not match!", Toast.LENGTH_SHORT).show();
            }
        }
        catch(Exception e)
        {
            Toast.makeText(getApplicationContext(), e.getMessage(), Toast.LENGTH_LONG).show();
        }

这是我的数据库类 Activity ，

创建表时，

public void onCreate(SQLiteDatabase db) 
    {
        try
        {
            String CREATE_POLLINGDATA_TABLE="CREATE TABLE pollingdata(username TEXT, userid PRIMARY KEY, password TEXT)";
            db.execSQL(CREATE_POLLINGDATA_TABLE);
        }
        catch(SQLException e)
        {
            e.printStackTrace();
        }
    }

为输入的用户 ID 检索密码时，

public String getPasswordOfThisUser(String loginuserid)
{
    Cursor cursor=db.query("pollingdata", null, " userid=?" , new String[]{loginuserid}, null, null, null);
    if(cursor.getCount()<1)
    {
        cursor.close();
        return "Not Exist";
    }
    cursor.moveToFirst();
    String password= cursor.getString(cursor.getColumnIndex(KEY_PASSWORD));
    return password;
}

日志，

10-30 06:03:13.066: E/AndroidRuntime(13692): FATAL EXCEPTION: main
10-30 06:03:13.066: E/AndroidRuntime(13692): java.lang.NullPointerException
10-30 06:03:13.066: E/AndroidRuntime(13692):    at com.example.polling.LoginActivity.onClick(LoginActivity.java:47)
10-30 06:03:13.066: E/AndroidRuntime(13692):    at android.view.View.performClick(View.java:4204)
10-30 06:03:13.066: E/AndroidRuntime(13692):    at android.view.View$PerformClick.run(View.java:17355)
10-30 06:03:13.066: E/AndroidRuntime(13692):    at android.os.Handler.handleCallback(Handler.java:725)
10-30 06:03:13.066: E/AndroidRuntime(13692):    at android.os.Handler.dispatchMessage(Handler.java:92)
10-30 06:03:13.066: E/AndroidRuntime(13692):    at android.os.Looper.loop(Looper.java:137)
10-30 06:03:13.066: E/AndroidRuntime(13692):    at android.app.ActivityThread.main(ActivityThread.java:5041)
10-30 06:03:13.066: E/AndroidRuntime(13692):    at java.lang.reflect.Method.invokeNative(Native Method)
10-30 06:03:13.066: E/AndroidRuntime(13692):    at java.lang.reflect.Method.invoke(Method.java:511)
10-30 06:03:13.066: E/AndroidRuntime(13692):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
10-30 06:03:13.066: E/AndroidRuntime(13692):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
10-30 06:03:13.066: E/AndroidRuntime(13692):    at dalvik.system.NativeStart.main(Native Method)

我哪里错了？

请帮帮我，

谢谢。

Answer 1

试试这个

public String getPasswordOfThisUser(String loginuserid) {
    Cursor cursor = db.query("pollingdata", new String[] { KEY_PASSWORD },
            " userid=?", new String[] { username }, null, null, null);
    if (cursor.getCount() < 1) {
        cursor.close();
        return "Not Exist";
    }
    cursor.moveToFirst();
    String password = cursor.getString(cursor.getColumnIndex(KEY_PASSWORD));
    return password;
}

返回密码前必须关闭光标