android ContentProvider讲解
ContentProvider讲解
当应用A需要通过contentProvider共享数据时，应按如下顺序进行操作：
一. 定义一个MyProviderextends android.content.ContentProvider并重写里面的onCreate，getType，insert,delete,query,update六个方法。将定义好的MyProvider在manifest.xml中进行声明注册。
1. MyProvider中需要定义一个UriMatcher对象，并在其上注册Provider提供的Uri，返回对应的匹配码，若无匹配，则返回-1；具体如下：
public static UriMatcher uriMatcher;
static{
uriMatcher= new UriMatcher(UriMatcher.NO_MATCH);
uriMatcher.addURI(AUTHORITY,"user", MATCH_DIR);// 添加需要匹配uri，如果匹配就会返回匹配码，没有匹配的，返回-1
uriMatcher.addURI(AUTHORITY,"user/#", MATCH_ITEM);// 如果match()方法匹配content://com.unj.myprovider/user/230路径，返回匹配码为2
}
2.对于重写的增删查改四个方法，sql语句对应的相应方法的参数参照如下：
/**
* select id, name from user where age = ? order by name 对应下面的参数为
* projection = new String{"id","name"};
* selection = "age = ?";
* selectionArgs = new String{"23"};
* sortOrder = "name";
*/
@Override
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder)
3. 我们可以根据Uri来添加查询条件：
switch (uriMatcher.match(uri)) {
case MATCH_DIR:
break;
case MATCH_ITEM:
long id = ContentUris.parseId(uri);
if (selection != null && !"".equals(selection)) {
selection += " and ";
}
selection += " id = " + id;
break;
default:
throw new IllegalArgumentException("Unkonw URI" + uri);
}
4. 当增删查改操作使数据发生变化时，可调用如下方法通知调用此ContentProvider的ContentResolver，数据发生了变化。
getContext().getContentResolver().notifyChange(uri, null);//通知，调用此uri的resolver，数据已经发生变化，调用端的ContentObserver会回调onChange方法。
5.如下是我自定义的操纵数据库的一个Provider：MyDBUserProvider.java
package com.androidstudydemo.contentprovider;
import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;
/**
* 当应用需要通过ContentProvider对外共享数据时，第一步需要继承ContentProvider并重写下面六个方法
* 第二步需要在AndroidManifest.xml使用<provider>对该ContentProvider进行配置
* 详细参见：http://www.cnblogs.com/linjiqin/archive/2011/05/28/2061396.html
*
* @author zkx016
*
*/
public class MyDBUserProvider extends ContentProvider {
public static final String AUTHORITY = "com.unj.myprovider";
public static final String TABLE_NAME = "user";
public static final Uri CONTENT_URI = Uri.parse("content://" + AUTHORITY
+ "/user");
public static final int MATCH_DIR = 1;
public static final int MATCH_ITEM = 2;
MyDBHelper myDBHelper;
/**
* 该ContentProvider所返回的数据类型定义
*/
public static final String CONTENT_TYPE_DIR = "vnd.android.cursor.dir/user";// 返回集合类型的数据
public static final String CONTENT_TYPE_ITEM = "vnd.android.cursor.item/user";// 返回非集合类型的数据
/**
* UriMatcher类用于匹配Uri，首先第一步把你需要匹配Uri路径全部给注册上，
*/
public static UriMatcher uriMatcher;
static {
uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
uriMatcher.addURI(AUTHORITY, "user", MATCH_DIR);// 添加需要匹配uri，如果匹配就会返回匹配码
uriMatcher.addURI(AUTHORITY, "user/#", MATCH_ITEM);// 如果match()方法匹配content://com.unj.myprovider/person/230路径，返回匹配码为2
}
/**
* 该方法在ContentProvider创建后就会被调用，Android开机后，ContentProvider在其它应用第一次访问它时才会被创建。
*/
@Override
public boolean onCreate() {
myDBHelper = new MyDBHelper(getContext());// 这里的实现，常见前篇关于Sqlite的文章。
return true;
}
/**
* 该方法用于返回当前Url所代表数据的MIME类型。
* 如果操作的数据属于集合类型，那么MIME类型字符串应该以vnd.android.cursor.dir/开头，
* 例如：要得到所有person记录的Uri为content://com.ljq.provider.personprovider/person，
* 如果操作的数据不属于集合类型那么返回的MIME类型字符串应该为："vnd.android.cursor.dir/person"。
* 如果要操作的数据属于非集合类型数据，那么MIME类型字符串应该以vnd.android.cursor.item/开头，
*/
@Override
public String getType(Uri uri) {
switch (uriMatcher.match(uri)) {// 进行匹配
case MATCH_DIR:
return CONTENT_TYPE_DIR;
case MATCH_ITEM:
return CONTENT_TYPE_ITEM;
default:
throw new IllegalArgumentException("Unknown URI" + uri);
}
}
/**
* 该方法用于供外部应用往ContentProvider添加数据。
*/
@Override
public Uri insert(Uri uri, ContentValues values) {
int type = uriMatcher.match(uri);
if (type != MATCH_DIR) {
throw new IllegalArgumentException("Unknown URI:" + uri);
}
SQLiteDatabase db = myDBHelper.getWritableDatabase();
long rowId = db.insert(TABLE_NAME, null, values);// 返回的是受影响的那一行的行号，出错时返回-1；
if (rowId > 0) {
/**
* withAppendedId(uri, id)用于为路径加上ID部分,
* 生成后的Uri为：content://com.unj.myprovider/person/10
*/
Uri noteUri = ContentUris.withAppendedId(CONTENT_URI, rowId);
/**
* 如果ContentProvider的访问者需要知道ContentProvider中的数据发生变化，
* 可以在ContentProvider发生数据变化时调用getContentResolver().notifyChange(uri,
* null)来通知注册在此URI上的访问者，
*/
getContext().getContentResolver().notifyChange(uri, null);
db.close();
return noteUri;
} else {
db.close();
throw new IllegalArgumentException("Failed to insert row into"
+ uri);
}
}
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
SQLiteDatabase db = myDBHelper.getWritableDatabase();
switch (uriMatcher.match(uri)) {
case MATCH_DIR:
break;
case MATCH_ITEM:
long id = ContentUris.parseId(uri);
if (selection != null && !"".equals(selection)) {
selection += " and ";
}
selection += " id = " + id;
break;
default:
throw new IllegalArgumentException("Unkonw URI" + uri);
}
int rows = db.delete(TABLE_NAME, selection, selectionArgs);
if (rows > 0) {
getContext().getContentResolver().notifyChange(uri, null);
db.close();
return rows;
} else {
db.close();
throw new IllegalArgumentException("Failed to delete row in" + uri);
}
}
/**
* select id, name from user where age = ? order by name 对应下面的参数为 projection
* = new String{"id","name"}; selection = "age = ?"; selectionArgs = new
* String{"23"}; sortOrder = "name";
*/
@Override
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
switch (uriMatcher.match(uri)) {
case MATCH_DIR:
// tableName = uri.getLastPathSegment();
break;
case MATCH_ITEM:
long id = ContentUris.parseId(uri);
if (selection != null && !"".equals(selection)) {
selection += " and ";
}
selection += "id = " + id;
break;
default:
throw new IllegalArgumentException("Unkonw URI" + uri);
}
SQLiteDatabase db = myDBHelper.getReadableDatabase();
Cursor cursor = db.query(TABLE_NAME, projection, selection,
selectionArgs, null, null, sortOrder);
cursor.setNotificationUri(getContext().getContentResolver(), uri);// @1
return cursor;
}
@Override
public int update(Uri uri, ContentValues values, String selection,
String[] selectionArgs) {
switch (uriMatcher.match(uri)) {
case MATCH_DIR:
break;
case MATCH_ITEM:
long id = ContentUris.parseId(uri);
if (selection != null && !"".equals(selection)) {
selection += " and ";
}
selection += "id = " + id;
break;
default:
throw new IllegalArgumentException("Unkonw URI" + uri);
}
SQLiteDatabase db = myDBHelper.getWritableDatabase();
int rowsAffected = db.update(TABLE_NAME, values, selection,
selectionArgs);//返回受影响的行数
db.close();
if (rowsAffected > 0) {
getContext().getContentResolver().notifyChange(CONTENT_URI, null);// @2
return rowsAffected;
}
return 0;
}
}
6.MyProvider定义完成之后，需要在manifest.xml中进行Provider的注册，具体在<application></application>内部：
<!-- 自定义contentProvider-->
<provider
android:name="com.androidstudydemo.contentprovider.MyDBUserProvider"
android:authorities="com.unj.myprovider" >
</provider>
二. 在其他应用（B）中可以对应的通过Context获得ContentResolver，ContentResolver里面有和ContentProvider相对应的增删查改四个方法，在B应用中直接调用contentResolver.insert()等方法就会获得A应用中提供的数据，B在调用时必须保证A应用同时在运行。
1. 新建一个android project，声明自己需要数据的Uri和authority：
public static final String AUTHORITY = "com.unj.myprovider";
public static final Uri CONTENT_URI = Uri.parse("content://" + AUTHORITY
+ "/user");
2.定义一个ContentObserver，重写里面的onChange（boolean selfChange, Uri uri）方法，它的作用是当Provider里面对应的Uri数据发生变化，此方法将会被回调。
private ContentObserver contentObserver = new ContentObserver(handler) {
public void onChange(boolean selfChange, Uri uri) {
Toast.makeText(MainActivity.this, "数据发生改变， uri is:" + uri,
Toast.LENGTH_SHORT).show();
queryClick();
};
};
3,在应用中通过getContext().getContentResolver() 获得ContentResolver，并注册ContentObserver
<span style="white-space:pre"> </span>resolver = getContentResolver(); /** * 如果ContentProvider的访问者需要得到数据变化通知，必须使用ContentObserver对数据（数据采用uri描述）进行监听 * ，当监听到数据变化通知时，系统就会调用ContentObserver的onChange()方法 */ resolver.registerContentObserver(CONTENT_URI, false, contentObserver);4. 如下是我自定义的Bproject，用来测试上方的Provider：
package com.example.providertest;
import android.app.Activity;
import android.content.ContentResolver;
import android.content.ContentUris;
import android.content.ContentValues;
import android.database.ContentObserver;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends Activity implements OnClickListener {
public static final String AUTHORITY = "com.unj.myprovider";
public static final Uri CONTENT_URI = Uri.parse("content://" + AUTHORITY
+ "/user");
private ContentResolver resolver;
private TextView textView;
private Button query;
private int id = 0;
Handler handler = new Handler();
private ContentObserver contentObserver = new ContentObserver(handler) {
public void onChange(boolean selfChange, Uri uri) {
Toast.makeText(MainActivity.this, "数据发生改变， uri is:" + uri,
Toast.LENGTH_SHORT).show();
queryClick();
};
};
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
query = (Button) this.findViewById(R.id.button2);
resolver = getContentResolver();
/**
* 如果ContentProvider的访问者需要得到数据变化通知，必须使用ContentObserver对数据（数据采用uri描述）进行监听
* ，当监听到数据变化通知时，系统就会调用ContentObserver的onChange()方法
*/
resolver.registerContentObserver(CONTENT_URI, false, contentObserver);
textView = (TextView) findViewById(R.id.textView1);
}
public Uri insertClick() {
ContentValues values = new ContentValues();
values.put("id", id);
values.put("name", "喻文杰" + id);
Uri uri = resolver.insert(CONTENT_URI, values);
id++;
return uri;
}
public void deleteClick() {
Cursor cursor = resolver.query(CONTENT_URI, null, null, null, null);
int count = cursor.getColumnCount();
if (count > 0 && cursor.moveToLast()) {
int id = resolver.delete(CONTENT_URI, "id = ?",
new String[] { cursor.getInt(cursor.getColumnIndex("id"))
+ "" });
} else {
Toast.makeText(MainActivity.this, "删除失败",
Toast.LENGTH_SHORT).show();
}
}
public void updateClick() {
Cursor cursor = resolver.query(CONTENT_URI, null, null, null, null);
if (cursor.moveToFirst()) {
ContentValues values = new ContentValues();
int id = cursor.getInt(cursor.getColumnIndex("id"));
values.put("name", "胡锦涛" + id);
Uri uri = ContentUris.withAppendedId(CONTENT_URI, id);
int result = resolver.update(uri, values, "", null);
}
if (!cursor.isClosed()) {
cursor.close();
}
}
public void queryClick() {
textView.setText("");
Cursor cursor = resolver.query(CONTENT_URI, null, null, null, null);
while (cursor.moveToNext()) {
textView.append("id : "
+ cursor.getInt(cursor.getColumnIndex("id")) + " ");
textView.append("name : "
+ cursor.getString(cursor.getColumnIndex("name")) + "\n");
}
if (!cursor.isClosed()) {
cursor.close();
}
textView.append("getAuthority:" + CONTENT_URI.getAuthority()
+ " \n********\n getEncodedAuthority:"
+ CONTENT_URI.getEncodedAuthority()
+ " \n********\n getEncodedFragment:"
+ CONTENT_URI.getEncodedFragment()
+ " \n********\ngetEncodedPath: "
+ CONTENT_URI.getEncodedPath() + " \n********\ngetHost: "
+ CONTENT_URI.getHost() + " \n********\ngetLastPathSegment: "
+ CONTENT_URI.getLastPathSegment() + " \n********\ngetPath: "
+ CONTENT_URI.getPath() + " \n********\ngetPort: "
+ CONTENT_URI.getPort() + " \n********\ngetQuery: "
+ CONTENT_URI.getQuery() + " \n********\ngetScheme: "
+ CONTENT_URI.getScheme() + " \n********\ngetUserInfo: "
+ CONTENT_URI.getUserInfo() + "\n********\n");
}
@Override
public void onClick(View arg0) {
switch (arg0.getId()) {
case R.id.button1:// 增
insertClick();
break;
case R.id.button3:// 删
deleteClick();
break;
case R.id.button2:// 查
queryClick();
break;
case R.id.button4:// 改
updateClick();
break;
default:
break;
}
}
}