这是我的代码....
StudentLogin.java类
public class StudentLogin extends Activity implements OnClickListener, OnItemSelectedListener{
Spinner sp1,sp2;
EditText reg;
Button b1,b2,b3;
String a1,a2,studreg,studdept,studyr;
SQLiteDatabase db1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_student_login);
reg=(EditText) findViewById(R.id.editText1);
sp1=(Spinner)findViewById(R.id.spinner1);
sp2=(Spinner)findViewById(R.id.spinner2);
b1=(Button)findViewById(R.id.button1);
b1.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
Cursor c=db1.rawQuery("Select * from StudReg", null); // Im getting an error here
int count=c.getCount();
int flag=0;
c.moveToFirst();
String regno=reg.getText().toString();
String yr=a1;
String dept=a2;
Toast.makeText(getApplicationContext(), regno, Toast.LENGTH_LONG).show();
if(regno.trim().length()>0&&!yr.equals("Select Year")&&!dept.equals("Select Dept"))
{
for(int i=0;i<count;i++)
{
studreg=c.getString(c.getColumnIndex("register"));
studdept=c.getString(c.getColumnIndex("deptmt"));
studyr=c.getString(c.getColumnIndex("year"));
if(regno.equals(studreg)&&yr.equals(studyr)&&dept.equals(studdept))
{
flag=1;
break;
}
c.moveToNext();
}
c.close();
if(flag==1)
{
Intent inn=new Intent(StudentLogin.this,StudyMaterials.class);
startActivity(inn);
}
else
{
Toast.makeText(getApplicationContext(), "Invalid User!\nKindly try again..", Toast.LENGTH_SHORT).show();
}
}
else
{
Toast.makeText(getApplicationContext(), "Kindly fill all the fields..", Toast.LENGTH_SHORT).show();
}
}
});
b2=(Button)findViewById(R.id.button2);
b2.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Intent intt=new Intent(StudentLogin.this,StudentRegister.class);
startActivity(intt);
}
});
b3=(Button)findViewById(R.id.button3);
b3.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Intent int1=new Intent(StudentLogin.this,Update.class);
startActivity(int1);
}
});
sp1.setOnItemSelectedListener(new OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> p, View v,
int a, long l) {
// TODO Auto-generated method stub
a1=p.getItemAtPosition(a).toString();
//Toast.makeText(getApplicationContext(), a1, Toast.LENGTH_LONG).show();
}
@Override
public void onNothingSelected(AdapterView<?> arg0) {
// TODO Auto-generated method stub
}
});
sp2.setOnItemSelectedListener(new OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> p, View v,
int a, long l) {
// TODO Auto-generated method stub
a2=p.getItemAtPosition(a).toString();
//Toast.makeText(getApplicationContext(), a2, Toast.LENGTH_LONG).show();
}
@Override
public void onNothingSelected(AdapterView<?> arg0) {
// TODO Auto-generated method stub
}
});
List<String> categories = new ArrayList<String>();
categories.add("Select Department");
categories.add("CSE");
categories.add("IT");
categories.add("CIVIL");
categories.add("MECH");
categories.add("ECE");
categories.add("EEE");
ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_dropdown_item, categories);
dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
sp2.setAdapter(dataAdapter);
List<String> categories1 = new ArrayList<String>();
categories1.add("Select Year");
categories1.add("I");
categories1.add("II");
categories1.add("III");
categories1.add("IV");
ArrayAdapter<String> dataAdapter1 = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_dropdown_item, categories1);
dataAdapter1.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
sp1.setAdapter(dataAdapter1);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.student_login, menu);
return true;
}
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
}
@Override
public void onItemSelected(AdapterView<?> p, View v, int it,
long l) {
// TODO Auto-generated method stub
}
@Override
public void onNothingSelected(AdapterView<?> arg0) {
// TODO Auto-generated method stub
}
}
此代码验证用户是否已注册。 请帮我解决这个错误...
答案 0 :(得分：0)
您需要初始化数据库
//dbHelper its a helper class for database
database = dbHelper.getWritableDatabase();
答案 1 :(得分：0)
你已经给出了表名，但是你没有说明表存在哪个db（因为db1没有被初始化）。所以请按照@Madhur的答案来解决这个空指针异常。还有一个使用db的建议（更好）使用加载器而不是在MainThread上工作。）