对我来说，问题是我想从sqlite数据库中获取特定Id的数据，如果数据库中的那个ID不存在，我需要显示一条消息，说明无效的ID，问题出在我的代码中是否有效Id匹配。但是当数据库没有我搜索的值时，我的应用程序崩溃了。我是一个编程的新手我知道这是我的逻辑中的错误，我把这个。请帮助。经过几次
package com.my.myapp;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class DBSqliteAddSTDinfo {
public static final String KEY_STDNO = "S_no";
public static final String KEY_NAME = "First_Name";
public static final String KEY_AGE = "Age";
private static final String DBNAME = "second";
private static final String TBLNAME = "details";
private static final int DBversion = 1;
private DbHelper OurHelper;
private final Context OurContext;
private SQLiteDatabase OurDatabase;
private static class DbHelper extends SQLiteOpenHelper {
public DbHelper(Context context) {
super(context, DBNAME, null, DBversion);
// TODO Auto-generated constructor stub
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
db.execSQL("CREATE TABLE " + TBLNAME + " (" +
KEY_STDNO + " INTEGER PRIMARY KEY, " +
KEY_NAME + " TEXT NOT NULL, " +
KEY_AGE + " TEXT NOT NULL);"
);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
db.execSQL("DROP TABLE IF EXISTS " + TBLNAME );
onCreate(db);
}
}
public DBSqliteAddSTDinfo(Context c){
OurContext = c;
}
public DBSqliteAddSTDinfo open()throws SQLException{
OurHelper = new DbHelper(OurContext);
OurDatabase = OurHelper.getWritableDatabase();
return this;
}
public void close(){
if (OurDatabase != null){
OurDatabase.close();
OurHelper.close();
}
}
/*EditText editID,editFname,editLname,editDOB,editSname,editGrade_Year,editClass;
Button Submit;
SQLiteDatabase db;*/
public long creatEntry(String Id, String Name, String Age) {
// TODO Auto-generated method stub
ContentValues cv = new ContentValues();
cv.put(KEY_STDNO, Id);
cv.put(KEY_NAME, Name);
cv.put(KEY_AGE, Age);
return OurDatabase.insert(TBLNAME, null, cv);
}
public String getName(long l) {
// TODO Auto-generated method stub
String[] columns = new String[]{ KEY_STDNO, KEY_NAME, KEY_AGE};
Cursor c = OurDatabase.query(TBLNAME, columns, KEY_STDNO + "=" + l, null, null, null, null);
if(c != null){
c.moveToFirst();
String name = c.getString(1);
return name;
}
return null;
}
public String getAge(long l) {
// TODO Auto-generated method stub
String[] columns = new String[]{ KEY_STDNO, KEY_NAME, KEY_AGE};
Cursor c = OurDatabase.query(TBLNAME, columns, KEY_STDNO + "=" + l, null, null, null, null);
if(c != null){
c.moveToFirst();
String age = c.getString(2);
return age;
}
return null;
}
public void updateEntry(long lRow, String sname, String sage) {
// TODO Auto-generated method stub
ContentValues update = new ContentValues();
update.put(KEY_NAME, sname);
update.put(KEY_AGE, sage);
OurDatabase.update(TBLNAME, update, KEY_STDNO + "=" + lRow, null);
}
public void deleteEntry(long lRowdel) {
// TODO Auto-generated method stub
OurDatabase.delete(TBLNAME, KEY_STDNO + "=" + lRowdel, null);
}
public String getNo(long l) {
// TODO Auto-generated method stub
String[] columns = new String[]{ KEY_STDNO, KEY_NAME, KEY_AGE};
Cursor c = OurDatabase.query(TBLNAME, columns, KEY_STDNO + "=" + l, null, null, null, null);
if(c != null){
c.moveToFirst();
String sno = c.getString(0);
return sno;
}
return null;
}
}
package com.my.myapp;
import android.app.AlertDialog.Builder;
import android.app.Dialog;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import com.my.myapp.DBSqliteAddSTDinfo;
public class ViewData extends ActionBarActivity {
EditText id,name,age,ID;
Button ViewData,Update;
@SuppressWarnings("static-access")
public void onClick(View v){
id = (EditText)findViewById(R.id.ViewId);
name = (EditText)findViewById(R.id.ViewName);
age = (EditText)findViewById(R.id.ViewAge);
ID = (EditText)findViewById(R.id.editTextID);
ViewData = (Button) findViewById(R.id.btnViewData);
DBSqliteAddSTDinfo hon = new DBSqliteAddSTDinfo(this);
hon.open();
if(id.getText().toString().trim().length()==0)
{
Dialog d = new Dialog(ViewData.this);
d.setTitle("ID Can Not Be Empty");
TextView tv = new TextView(ViewData.this);
tv.setText("Unsuccessful ! ");
d.setContentView(tv);
d.show();
return;
}
String s = id.getText().toString();
long l = Long.parseLong(s);
String returnedName = hon.getName(l);
String returnedAge = hon.getAge(l);
String returnedSno = hon.getNo(l);
//String NewSno = Long.toString(l);
if(returnedSno.equals(s)){
name.setText(returnedName);
age.setText(returnedAge);
ID.setText(returnedSno);
/*Dialog d = new Dialog(ViewData.this);
d.setTitle("Invalied ID");
TextView tv = new TextView(ViewData.this);
tv.setText("Unsuccessful ! ");
d.setContentView(tv);
d.show();*/
//return;
}
if(hon.getNo(l)== null && hon.getName(l)== null && hon.getAge(l)== null ){
Dialog d = new Dialog(ViewData.this);
d.setTitle("Invalied ID");
TextView tv = new TextView(ViewData.this);
tv.setText("Unsuccessful ! ");
d.setContentView(tv);
d.show();
//return;
/*name.setText(returnedName);
age.setText(returnedAge);
ID.setText(returnedSno); */
}
hon.close();
}
private void clearText() {
// TODO Auto-generated method stub
id.setText("");
name.setText("");
age.setText("");
}
private void showMessage(String title, String message) {
// TODO Auto-generated method stub
{
Builder builder=new Builder(this);
builder.setCancelable(true);
builder.setTitle(title);
builder.setMessage(message);
builder.show();
}
}
public void onClickUpdate(View v){
String sname = name.getText().toString();
String sage = age.getText().toString();
String sRow = id.getText().toString();
long lRow = Long.parseLong(sRow);
DBSqliteAddSTDinfo upd = new DBSqliteAddSTDinfo(this);
upd.open();
upd.updateEntry(lRow, sname, sage);
upd.close();
}
public void onClickDelete(View v){
String sRowdel = id.getText().toString();
long lRowdel = Long.parseLong(sRowdel);
DBSqliteAddSTDinfo del = new DBSqliteAddSTDinfo(this);
del.open();
del.deleteEntry(lRowdel);
del.close();
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_view_data);
/*id = (EditText)findViewById(R.id.ViewId);
name = (EditText)findViewById(R.id.ViewName);
age = (EditText)findViewById(R.id.ViewAge);
ViewData = (Button) findViewById(R.id.btnViewData);
String s = id.getText().toString();
long l = Long.parseLong(s);
DBSqliteAddSTDinfo hon = new DBSqliteAddSTDinfo(this);
hon.open();
String returnedName = hon.getName(l);
String returnedAge = hon.getAge(l);
name.setText(returnedName);
age.setText(returnedAge);
hon.close(); */
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.view_data, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
答案 0 :(得分：2)
更改
if(c != null){
c.moveToFirst();
到
if(c.moveToFirst()){
游标不会为空，您需要检查moveToFirst()的返回值，以查看游标是否包含任何行，然后才能使用getString()访问其数据。