问题描述
我想实现一个操作多个表的 ContentProvider
。这是我到目前为止所尝试的。我写了一个Java 接口
,表示每个表应该在其CRUD类中实现的CRUD操作。
I want to implement a ContentProvider
that manipulates multiple tables. Here is what I tried so far. I wrote a Java Interface
that represents the CRUD operations that every table should implement in its CRUD class.
public interface CRUDHandler {
//UPDATE
int update(Uri uri, ContentValues values, String selection,String[] selectionArgs);
//READ
Cursor query(Uri uri, String[] projection, String selection,String[] selectionArgs, String sortOrder) ;
//CREATE
Uri insert(Uri uri, ContentValues values);
//DELETE
int delete(Uri uri, String selection, String[] selectionArgs);
//get Mime type
String getType(Uri uri);
}
然后我写了一个抽象
class 定义了 ContentProvider
的静态 UriMatcher
所以每个类扩展
这个类应该添加它的 Uri
来标识它,并为接口中的每个方法提供一个实现。
Then I wrote an abstract
class
that defines a static UriMatcher
for the ContentProvider
so each class that extends
this class should add its Uri
that identifies it and provide an implementation for each method in interface.
类看起来像这样:
public abstract class ApplicationCRUD implements CRUDHandler{
public static final UriMatcher sUriMatcher;
static {
sUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
}
}
此外,我为每个表创建了一个类, code> extends 这个类,并将 Uri
添加到 UriMatcher
来自抽象类。
Further, I created a class for each table that extends
this class and adds its Uri
's to the UriMatcher
from the abstract class.
这是一个例子:
public class Table1CRUD extends ApplicationCRUD {
//Setup Projection Map for Table1
private static HashMap<String , String>sTable1ProjectionMap;
static {
sTable1ProjectionMap.put(ApplicationProviderMetaData.Table1MetaData._ID, ApplicationProviderMetaData.Table1MetaData.TABLE_NAME+"."+ApplicationProviderMetaData.Table1MetaData._ID);
sTable1ProjectionMap.put(ApplicationProviderMetaData.Table1MetaData.COL1, ApplicationProviderMetaData.Table1MetaData.TABLE_NAME+"."+ApplicationProviderMetaData.Table1MetaData.COL1);
sTable1ProjectionMap.put(ApplicationProviderMetaData.Table1MetaData.COL2, ApplicationProviderMetaData.Table1MetaData.TABLE_NAME+"."+ApplicationProviderMetaData.Table1MetaData.COL2);
}
public static final int INCOMING_SINGLE_URI_INDICATOR = 5;
public static final int INCOMING_COLLECTION_URI_INIDICATOR = 6;
static {
//standard URI
sUriMatcher.addURI(ApplicationProviderMetaData.AUTHORITY, "t1", INCOMING_COLLECTION_URI_INIDICATOR);
sUriMatcher.addURI(ApplicationProviderMetaData.AUTHORITY, "t1/#", INCOMING_SINGLE_URI_INDICATOR);
//here add your custom URI
}
@Override
public int update(Uri uri, ContentValues values, String selection,
String[] selectionArgs) {
// TODO Auto-generated method stub
return 0;
}
@Override
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
// TODO Auto-generated method stub
return null;
}
@Override
public Uri insert(Uri uri, ContentValues values) {
// TODO Auto-generated method stub
return null;
}
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
// TODO Auto-generated method stub
return 0;
}
@Override
public String getType(Uri uri) {
// TODO Auto-generated method stub
return null;
}
}
现在我的 ContentProvider
看起来像这样:
Now my ContentProvider
looks like this:
public class ApplicationProvider extends ContentProvider{
//Define TAG FOR EACH CLASS FOR DEBUGGING
private static final String TAG = "ApplicationProvider";
// Application CRUD Handlers use to support multiple tables inside the content provider
private static Table1CRUD table1CRUD;
private static Table2CRUD table2CRUD;
static {
table1CRUD = new Table1CRUD();
table2CRUD= new Table2CRUD();
}
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
int uriMatchResult = ApplicationCRUD.sUriMatcher.match(uri);
//case Table1
if(uriMatchResult == Table1CRUD.INCOMING_COLLECTION_URI_INIDICATOR ||uriMatchResult == Table1CRUD.INCOMING_SINGLE_URI_INDICATOR )
{
return table1CRUD.delete(uri, selection, selectionArgs);
}
case Table2
else if(uriMatchResult == Table2.INCOMING_COLLECTION_URI_INDICATOR|| uriMatchResult ==Table2.INCOMING_SINGLE_URI_INDICATOR){
return table2CRUD.delete(uri, selection, selectionArgs);
}
else{
throw new IllegalArgumentException("Unknown Uri "+uri);
}
}
现在我使用 SQLiteOpenHelper
作为 ContentProvider
中的私有类,我在我的 ContentProvider
。应该修改接口并提供对象依赖注入
的每个CRUD方法,让每个函数使用它来访问数据库?我也想知道你对这种方法的看法:是否够好?这是否使我想要有效地做的事情?
Now I am using the SQLiteOpenHelper
as a private class in the ContentProvider
and I define an instance of it in my ContentProvider
. Should I modify the interface and supply each CRUD method that object Dependency Injection
to let each function use it to access the database? I also want to know what you think about this approach: Is it good enough? Does it make the thing I am trying to do efficiently? What modification can I do to improve this design?
推荐答案
应用程序是一个很好的资源,如果你需要设计一个具有多个表的 ContentProvider
。听起来你想做一些更复杂的事情,但也许会有所帮助。
The Google IO Schedule application is a good resource if you are need to design a ContentProvider
with multiple tables. It sounds like you want to do something a bit more complicated, but maybe it will help.
这篇关于ContentProvider具有多个表的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!