我无法让我的登录屏幕正常工作。用户应输入他们的登录名和密码，然后将其与包含先前注册的数据库进行比较。有人可以告诉我哪里出错了，为什么代码不起作用？
**Login.java**
package com.B00512756.angertwo;
import android.app.Activity;
import android.content.ContentValues;
import android.content.Context;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
public class Login extends Activity implements OnClickListener{
public static final String DATABASE_NAME = "login_database.db";
public static final String USER_INFO_TABLE = "user_information";
public static final String COLUMN_ID = "UserID";
public static final String COLUMN_RATING = "UserName";
public static final String COLUMN_NAME = "Password";
public EditText txtUserName;
public EditText txtPassword;
public static Button btnLogin;
public static Button btnCancel;
/** Called when the activity is first created. */
@SuppressWarnings("unused")
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.loginpage);
txtUserName=(EditText)this.findViewById(R.id.txtUname);
txtPassword=(EditText)this.findViewById(R.id.txtPwd);
//btnLogin=(Button)this.findViewById(R.id.btnLogin);
Button Login = (Button) findViewById(R.id.btnLogin);
Button Register = (Button) findViewById(R.id.btnregister);
Button Cancel = (Button) findViewById(R.id.btnCancel);
Register.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
Intent myIntent = new Intent(view.getContext(), Registration.class);
startActivityForResult(myIntent, 0);
finish();
}
});
Cancel.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
android.os.Process.killProcess(android.os.Process.myPid());
}
});
Login.setOnClickListener(new View.OnClickListener() {
@SuppressWarnings("null")
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
String name = txtUserName.getText().toString();
String pwd = txtPassword.getText().toString();
SQLiteDatabase regDB = null;
//String[] columns = new String[]{COLUMN_ID, COLUMN_RATING, COLUMN_NAME };
try {
Cursor c = regDB.query(USER_INFO_TABLE, new String[] {
COLUMN_ID, COLUMN_RATING, COLUMN_NAME}, null, null, null, null, null);
if(null!=c){
c.moveToFirst();
System.out.println("Cursor Size"+c.getCount());
}
String result = "";
int iRow = c.getColumnIndex(COLUMN_ID);
int iRating = c.getColumnIndex(COLUMN_RATING);
int iName = c.getColumnIndex(COLUMN_NAME);
c.moveToLast();
for (int i = c.getCount() - 1; i >= 0; i--) {
// Get the data
result = result + c.getString(iRow) + " " + c.getString(iRating) + " " + c.getString(iName) + "\n" ;
if("select * from USER_INFO_TABLE where UserName =" + "\""+ name + "\""+" and Password="+ "\""+ pwd != null );
{ Intent j = new Intent();
j.setClassName("com.B00512756.angertwo",
"com.B00512756.angertwo.AngerprototypetwoActivity");
startActivity(j);}
// Move the cursor
c.moveToPrevious();
}
c.close();
}
catch (Exception e)
{
}
}
});
}
private SQLiteDatabase getWritableDatabase() {
// TODO Auto-generated method stub
return null;
}
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
}
}
**AndroidMainfest:**
<?xml version="1.0" encoding="utf-8"?>
<manifest package="com.B00512756.angertwo"
android:versionCode="1"
android:versionName="1.0" xmlns:android="http://schemas.android.com/apk/res/android">
<uses-sdk android:minSdkVersion="8" />
<application android:name=".AppState" android:icon="@drawable/icon" android:label="@string/app_name">
<activity android:name=".Login"
android:label="@string/main_title">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".Login" android:label="@string/begin_label"
android:theme="@android:style/Theme"></activity>
<activity android:name=".Question1" android:label="@string/question_one"
android:theme="@android:style/Theme"></activity>
<activity android:name=".Question2" android:label="@string/question_two"
android:theme="@android:style/Theme"></activity>
<activity android:name=".Question3" android:label="@string/question_three"
android:theme="@android:style/Theme"></activity>
<activity android:name=".Question4" android:label="@string/question_four"
android:theme="@android:style/Theme"></activity>
<activity android:name=".Question5" android:label="@string/question_five"
android:theme="@android:style/Theme"></activity>
<activity android:name=".AngerprototypetwoActivity" android:label="@string/main_title"
android:theme="@android:style/Theme"></activity>
<activity android:name=".nextQ1" android:id="@+id/next_Q1_button"
android:theme="@android:style/Theme"></activity>
<activity android:name=".Strategies" android:label="@string/strategies_label"
android:theme="@android:style/Theme"></activity>
<activity android:name=".Contact" android:label="@string/begin_label"
android:theme="@android:style/Theme"></activity>
<activity android:name=".Strat_What_Is_Anger" android:label="@string/strategies_label_what_is_anger"
android:theme="@android:style/Theme"></activity>
<activity android:name=".Strat_Use_Distraction" android:label="@string/strategies_label_distraction"
android:theme="@android:style/Theme"></activity>
<activity android:name=".Registration" android:label="@string/registration"
android:theme="@android:style/Theme"></activity>
</application>
</manifest>