在实现内容提供程序时，我在检索数据时遇到错误“说：无法从游标窗口读取第0行-1列”。我的代码，主要活动和错误日志如下。
package com.example.contentprovider;
import java.util.HashMap;
public class StudentsProvider extends ContentProvider{
static final String PROVIDER_NAME="com.example.contentprovider";
static final String URL="content://" + PROVIDER_NAME + "/students";
static final Uri CONTENT_URI=Uri.parse(URL);
static final String _ID="id";
static final String NAME="name";
static final String GRADE="grade";
private static HashMap<String,String>STUDENTS_PROJECTION_MAP;
static final int STUDENTS=1;
static final int STUDENT_ID=2;
static final UriMatcher uriMatcher;
static{
uriMatcher=new UriMatcher(UriMatcher.NO_MATCH);
uriMatcher.addURI(PROVIDER_NAME, "students", STUDENTS);
uriMatcher.addURI(PROVIDER_NAME, "students/#", STUDENT_ID);
}
//Database specific constant declarations
private SQLiteDatabase db;
static final String DATABASE_NAME="College";
static final String STUDENTS_TABLE_NAME="students";
static final int DATABASE_VERSION=1;
static final String CREATE_DB_TABLE=" CREATE TABLE " + STUDENTS_TABLE_NAME +
" (_id INTEGER PRIMARY KEY AUTOINCREMENT, " +
" name TEXT NOT NULL, " +
" grade TEXT NOT NULL);";
// Helper class that actually creates and manages the providers underlying data
//repository
private static class DatabaseHelper extends SQLiteOpenHelper
{
public DatabaseHelper(Context context)
{
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
db.execSQL(CREATE_DB_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
db.execSQL("DROP TABLE IF EXISTS "+ STUDENTS_TABLE_NAME);
onCreate(db);
}
}
public boolean onCreate() {
// TODO Auto-generated method stub
Context context=getContext();
DatabaseHelper dbHelper=new DatabaseHelper(context);
/*
Create a write able database which will trigger its
creation if it doesn't already exist.
*/
db=dbHelper.getWritableDatabase();
return (db==null)?false:true;
}
public Uri insert(Uri uri, ContentValues values) {
//Adding a new student record
long rowID =db.insert(STUDENTS_TABLE_NAME, "", values);
//If record is added successfully
if(rowID>0)
{
Uri _uri=ContentUris.withAppendedId(CONTENT_URI, rowID);
getContext().getContentResolver().notifyChange(_uri, null);
return _uri;
}
throw new SQLException("Failed to add a record info " +uri);
}
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
SQLiteQueryBuilder qb=new SQLiteQueryBuilder();
qb.setTables(STUDENTS_TABLE_NAME);
switch(uriMatcher.match(uri))
{
case STUDENTS:
qb.setProjectionMap(STUDENTS_PROJECTION_MAP);
break;
case STUDENT_ID:
qb.appendWhere(_ID+ "=" + uri.getPathSegments().get(1));
break;
default:
throw new IllegalArgumentException("Unknown URI "+uri);
}
if(sortOrder==null || sortOrder=="")
{
sortOrder=NAME;
}
Cursor c=qb.query(db, projection, selection, selectionArgs, null, null, sortOrder);
//register to watch a content URI for changes
c.setNotificationUri(getContext().getContentResolver(), uri);
return c;
}
public int delete(Uri uri, String selection, String[] selectionArgs) {
int count = 0;
switch (uriMatcher.match(uri)){
case STUDENTS:
count = db.delete(STUDENTS_TABLE_NAME, selection, selectionArgs);
break;
case STUDENT_ID:
String id = uri.getPathSegments().get(1);
count = db.delete( STUDENTS_TABLE_NAME, _ID + " = " + id +
(!TextUtils.isEmpty(selection) ? " AND (" +
selection + ')' : ""), selectionArgs);
break;
default:
throw new IllegalArgumentException("Unknown URI " + uri);
}
getContext().getContentResolver().notifyChange(uri, null);
return count;
}
@Override
public int update(Uri uri, ContentValues values, String selection,
String[] selectionArgs) {
int count = 0;
switch (uriMatcher.match(uri)){
case STUDENTS:
count = db.update(STUDENTS_TABLE_NAME, values,
selection, selectionArgs);
break;
case STUDENT_ID:
count = db.update(STUDENTS_TABLE_NAME, values, _ID +
" = " + uri.getPathSegments().get(1) +
(!TextUtils.isEmpty(selection) ? " AND (" +
selection + ')' : ""), selectionArgs);
break;
default:
throw new IllegalArgumentException("Unknown URI " + uri );
}
getContext().getContentResolver().notifyChange(uri, null);
return count;
}
@Override
public String getType(Uri uri) {
switch (uriMatcher.match(uri)){
//Get all student records
case STUDENTS:
return "vnd.android.cursor.dir/vnd.example.students";
// Get a particular student
case STUDENT_ID:
return "vnd.android.cursor.item/vnd.example.students";
default:
throw new IllegalArgumentException("Unsupported URI: " + uri);
}
}
}
主要活动......
public void onClickRetrieveStudents(View view)
{ //Retrieving Students Records String URL="content://com.example.contentprovider/students";
Uri students=Uri.parse(URL);
Cursor c=managedQuery(students, null, null, null, "name");
if(c.moveToFirst())
{
do{ Toast.makeText(this, c.getString(c.getColumnIndex(StudentsProvider._ID)) + ", "+ c.getString(c.getColumnIndex(StudentsProvider.NAME)) + ", "+ c.getString(c.getColumnIndex(StudentsProvider.GRADE)), Toast.LENGTH_LONG).show(); } while(c.moveToNext()); }
}
错误日志：
10-25 01：00：15.523：I / Choreographer（826）：跳过93帧！应用程序可能在其主线程上做了太多工作 10-25 01：00：20.083：D / dalvikvm（826）：GC_FOR_ALLOC释放226K，13％空闲2794K / 3180K，暂停45ms，总计61ms 10-25 01：00：29.954：E / CursorWindow（826）：失败从CursorWindow中读取第0行，第-1列，其中包含5行3列 10-25 01：00：29.992：D / AndroidRuntime（826）：关闭VM 10-25 01：00：29.992：W / dalvikvm（826）：threadid = 1：线程退出未捕获异常（组= 0x41465700）< / p>
答案 0 :(得分：1)
初始化ID变量时出错：
static final String _ID="id"; // it must be "_id" value
因为您已创建了包含字段名称_id的表。 //_id INTEGER PRIMARY KEY AUTOINCREMENT