ContentProvider学习
ContentProvider是所有应用程序之间数据存储和检索的一个桥梁，作用是使得各个应用程序之间实现数据共享。
1.首先创建包含contentprovider的Content_uri和一些字段数据的NotePad类，字段类可以继承自BaseColumns类，代码如下
package com.lordbaby.ContentProvider;
import android.net.Uri;
import android.provider.BaseColumns;
public class NotePad {
//ContentProvider的Uri
public static final String AUTHORITY="com.google.provider.NotePad";
private NotePad(){}
//一些基本常量字段
public static final class Notes implements BaseColumns{
private Notes(){}
public static final Uri CONTENT_URI=Uri.parse("content://"+AUTHORITY+"/notes");
//新的MIME类型-多个
public static final String CONTENT_TYPE="vnd.android.cursor.dir/vnd.google.note";
//新的MIME类型-单个
public static final String CONTENT_ITEM_TYPE="vnd.android.cursor.item/vnd.google.note";
//默认的排序方式
public static final String DEFAULT_SORT_ORDER="modified DESC";
//字段
public static final String TITLE="title";
public static final String NOTE="note";
public static final String CREATEDDATE="created";
public static final String MODIFIEDDATE="modified";
}
}
2.然后创建自己的contentprovider类NotePadProvider，这里只写了查询和添加，以及打开创建数据库，具体实现代码如下
package com.lordbaby.ContentProvider;
import java.sql.SQLException;
import java.util.HashMap;
import java.util.ResourceBundle;
import com.lordbaby.ContentProvider.NotePad.Notes;
import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.Context;
import android.content.UriMatcher;
import android.content.res.Resources;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteQueryBuilder;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.net.Uri;
import android.text.TextUtils;
public class NotePadProvider extends ContentProvider {
private static final String TAG="NotePadProvider";
//数据库名
public static final String DATABASE_NAME="note_pad.db";
//数据库版本
public static final int DATABASE_VERSION=2;
//表名
public static final String NOTES_TABLE_NAME="notes";
public static HashMap<String,String> sNotesProjectionMap;
public static final int NOTES=1;
public static final int NOTE_ID=2;
public static final String CREATE_TABLE="CREATE TABLE "
+NOTES_TABLE_NAME
+"("+Notes._ID
+" INTEGER PRIMARY KEY,"
+Notes.TITLE
+" TEXT,"
+Notes.NOTE
+" TEXT,"
+Notes.CREATEDDATE
+" INTEGER,"
+Notes.MODIFIEDDATE
+" INTEGER"+");";
private DataBaseHelper mOpenHelper;
//用于匹配uri
public static final UriMatcher sUriMatcher;
static
{
System.out.println("start UriMatcher");
//常量UriMatcher.NO_MATCH表示不匹配任何路径的返回码
sUriMatcher=new UriMatcher(UriMatcher.NO_MATCH);
sUriMatcher.addURI(NotePad.AUTHORITY, "notes", NOTES);
sUriMatcher.addURI(NotePad.AUTHORITY, "notes/#", NOTE_ID);
//columnMap
sNotesProjectionMap=new HashMap<String, String>();
sNotesProjectionMap.put(Notes._ID, Notes._ID);
sNotesProjectionMap.put(Notes.TITLE, Notes.TITLE);
sNotesProjectionMap.put(Notes.NOTE, Notes.NOTE);
sNotesProjectionMap.put(Notes.CREATEDDATE, Notes.CREATEDDATE);
sNotesProjectionMap.put(Notes.MODIFIEDDATE, Notes.MODIFIEDDATE);
}
private static class DataBaseHelper extends SQLiteOpenHelper{
public DataBaseHelper(Context context) {
//在这并没有真正的创建或者打开数据库，而是在getWritableDatabase() or getReadableDatabase()
//被调用时才创建或者打开
super(context,DATABASE_NAME, null, DATABASE_VERSION);
// TODO Auto-generated constructor stub
}
//创建表
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
System.out.println("DataBaseHelper--------->onCreate Table");
db.execSQL(CREATE_TABLE);
}
//更新数据库
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
db.execSQL("DROP TABLE IF EXISTS notes");
onCreate(db);
}
}
@Override
public boolean onCreate() {
// TODO Auto-generated method stub
System.out.println("NotePadProvider-------->onCreate ");
mOpenHelper=new DataBaseHelper(getContext());
return true;
}
//查询操作
@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs,
String sortOrder) {
// TODO Auto-generated method stub
SQLiteQueryBuilder qb=new SQLiteQueryBuilder();
switch (sUriMatcher.match(uri)) {
case NOTES:
qb.setTables(NOTES_TABLE_NAME);
qb.setProjectionMap(sNotesProjectionMap);
break;
case NOTE_ID:
qb.setTables(NOTES_TABLE_NAME);
qb.setProjectionMap(sNotesProjectionMap);
//这里获取的是uri中path部分，去掉去掉"/"，的部分存于List<String>中，get(1)就是第二个值
//content://com.google.provider.NotePad/notes/1 path部分即notes/1
qb.appendWhere(Notes._ID+"="+uri.getPathSegments().get(1));
break;
default:
throw new IllegalArgumentException("Unkown URI"+uri);
}
String orderBy;
if (TextUtils.isEmpty(sortOrder)) {
orderBy=NotePad.Notes.DEFAULT_SORT_ORDER;
} else {
orderBy=sortOrder;
}
System.out.println("NotePadProvider------>query");
SQLiteDatabase db=mOpenHelper.getReadableDatabase();
Cursor c=qb.query(db, projection, selection, selectionArgs, null, null, orderBy);
c.setNotificationUri(getContext().getContentResolver(), uri);
return c;
}
//如果有自定义类型必须实现该方法
@Override
public String getType(Uri uri) {
// TODO Auto-generated method stub
System.out.println("NotePadProvider-------->getType");
switch (sUriMatcher.match(uri)) {
case NOTES:
//返回新的MIME类型-多个
return Notes.CONTENT_TYPE;
case NOTE_ID:
//返回新的MIME类型-单个
return Notes.CONTENT_ITEM_TYPE;
default:
throw new IllegalArgumentException("Unkown Uri:"+uri);
}
}
//插入数据库
@Override
public Uri insert(Uri uri, ContentValues initialValues) {
// TODO Auto-generated method stub
System.out.println("NotePadProvider---->insert");
if (sUriMatcher.match(uri)!=NOTES) {
throw new IllegalArgumentException("Unkown Uri:"+uri);
}
ContentValues values;
if (initialValues!=null) {
values=new ContentValues(initialValues);
} else {
values=new ContentValues();
}
Long now=Long.valueOf(System.currentTimeMillis());
if (values.containsKey(NotePad.Notes.CREATEDDATE)==false) {
values.put(NotePad.Notes.CREATEDDATE, now);
}
if (values.containsKey(NotePad.Notes.MODIFIEDDATE)==false) {
values.put(NotePad.Notes.MODIFIEDDATE, now);
}
if (values.containsKey(NotePad.Notes.TITLE)==false) {
Resources r=Resources.getSystem();
values.put(NotePad.Notes.TITLE, r.getString(android.R.string.untitled));
}
if (values.containsKey(NotePad.Notes.NOTE)==false) {
values.put(NotePad.Notes.NOTE, "");
}
SQLiteDatabase db=mOpenHelper.getWritableDatabase();
long rowId=db.insert(NOTES_TABLE_NAME, Notes.NOTE, values);
if (rowId>0) {
Uri noteUri=ContentUris.withAppendedId(NotePad.Notes.CONTENT_URI, rowId);
System.out.println("insert---------->"+noteUri.toString());
getContext().getContentResolver().notifyChange(noteUri, null);
return noteUri;
}
System.out.println("Failed to insert row into :"+uri);
return uri;
}
@Override
public int delete(Uri arg0, String arg1, String[] arg2) {
// TODO Auto-generated method stub
return 0;
}
@Override
public int update(Uri arg0, ContentValues arg1, String arg2, String[] arg3) {
// TODO Auto-generated method stub
return 0;
}
}
3.Androidmainfest.xml文件中必须声明
<provider android:name="NotePadProvider"
android:authorities="com.google.provider.NotePad"></provider>
