四大組件初始之ContentProvider
阿新 • • 發佈：2019-03-31
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在android中，除了存放在外部存儲的共享目錄下的數據，各個應用的數據庫文件，資源等都是私有的，其他應用沒有訪問權限。所以有了ContentProvider，不包含功能邏輯，用於不同應用進程間共享數據，是數據訪問的接口。
一、工作流程
為了快速熟悉ContentProvider的工作流程。先創建一個沒有具體實現的ContentProvider。
1、創建ContentProvider
只要繼承android提供的ContentProvider並實現抽象方法即可。
import android.content.ContentProvider;
import android.content.ContentValues;
import android.database.Cursor;
import android.net.Uri;
import android.os.Process;
import android.util.Log;
public class MyContentProvider extends ContentProvider {
private final static String Tag="ContentProvider";
public MyContentProvider() {
}
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
Log.d(Tag,"................delete");
return 0;
}
@Override
public String getType(Uri uri) {
return null;
}
@Override
public Uri insert(Uri uri, ContentValues values) {
Log.d(Tag,".................insert");
return null;
}
@Override
public boolean onCreate() {
Log.d(Tag,"..................onCreate,PID="+ Process.myPid());
return false;
}
@Override
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
Log.d(Tag,".................query");
return null;
}
@Override
public int update(Uri uri, ContentValues values, String selection,
String[] selectionArgs) {
Log.d(Tag,"...................update");
return 0;
}
}
2、註冊
應用的組件都要在清單文件裏面註冊。
為了說明ContentProvider工作在不同的進程間，使用process屬性。
3、訪問
使用URI定位一個ContentProvide，URI值為註冊時的authorities屬性。
import android.content.ContentResolver;
import android.net.Uri;
import android.os.Process;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
public class MainActivity extends AppCompatActivity {
private final static String Tag="MainActivity";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Log.d(Tag,"..............onCreate PID="+ Process.myPid());
Uri uri=Uri.parse("content://org.su.example.contentper");
ContentResolver contentResolver=getContentResolver();
contentResolver.query(uri,null,null,null,null);
contentResolver.query(uri,null,null,null,null);
contentResolver.delete(uri,null,null);
contentResolver.delete(uri,null,null);
}
}
ContentResolver是android提供訪問ContentProvide的類。
日誌輸出
二、數據形式
ContentProvide的接口看起來就像數據庫的操作，增刪改查。ContentProvide的數據形式也多是組織成表格的形式。每個表有多列。表的一行代表一個記錄。這就意味著我們要使用一個ContentProvide還要知道它有哪些表，表結構是什麽樣的。一般android提供的ContentProvide都有一個說明類。例如訪問android的圖片的表結構可以通過MediaStore.Images獲得，聯系人信息通過ContactsContract.Contacts獲得。
三、自定義完整的ContentProvider
很多文章的表結構用的是book(id,name,author);
使用SQLiteOpenHelper
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DbOpenHelper extends SQLiteOpenHelper {
private static final String DB_NAME = "book.db";
public static final String TABLE_NAME = "book";
private static final int DB_VERSION = 1;
// book表
private String CREATE_BOOK_TABLE = "CREATE TABLE IF NOT EXISTS "
+ TABLE_NAME + "(_id INTEGER PRIMARY KEY," + "name TEXT,"+" author TEXT)";
public DbOpenHelper(Context context) {
super(context,DB_NAME,null,DB_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(CREATE_BOOK_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db,int oldVersion,int newVersion){
// TODO ignored
}
}
BookProvider代碼
import android.content.ContentProvider;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;
import android.util.Log;
public class BookProvider extends ContentProvider {
private static final String TAG = "BookProvider";
public static final String AUTHORITY = "org.su.book.provider";
public static final Uri URI = Uri.parse("content://"
+ AUTHORITY + "/book");
private Context mContext;
private SQLiteDatabase mDb;
@Override
public boolean onCreate() {
Log.d(TAG,"onCreate,current thread:"+ Thread.currentThread().getName());
mContext = getContext();
//初始化數據
initProviderData();
return true;
}
private void initProviderData() {
mDb = new DbOpenHelper(mContext).getWritableDatabase();
mDb.execSQL("delete from " + DbOpenHelper.TABLE_NAME);
mDb.execSQL("insert into book values(3,‘Android‘,‘Android‘);");
mDb.execSQL("insert into book values(4,‘Ios‘,‘Ios‘);");
mDb.execSQL("insert into book values(5,‘Html5‘,‘web‘);");
}
@Override
public Cursor query(Uri uri,String[] projection,String selection,
String[] selectionArgs,String sortOrder) {
String table = getTableName(uri);
if (table == null) {
throw new IllegalArgumentException("Unsupported URI: " + uri);
}
return mDb.query(table,projection,selection,selectionArgs,null,
null,sortOrder,null);
}
@Override
public String getType(Uri uri) {
Log.d(TAG,"getType");
return null;
}
@Override
public Uri insert(Uri uri,ContentValues values) {
Log.d(TAG,"insert");
String table = getTableName(uri);
if (table == null) {
throw new IllegalArgumentException("Unsupported URI: " + uri);
}mDb.insert(table,null,values);
mContext.getContentResolver().notifyChange(uri,null);
return uri;
}
@Override
public int delete(Uri uri,String selection,String[] selectionArgs) {
Log.d(TAG,"delete");
String table = getTableName(uri);
if (table == null) {
throw new IllegalArgumentException("Unsupported URI: " + uri);
}
int count = mDb.delete(table,selection,selectionArgs);
if (count > 0) {
getContext().getContentResolver().notifyChange(uri,null);
}
return count;
}
@Override
public int update(Uri uri,ContentValues values,String selection,
String[] selectionArgs) {Log.d(TAG,"update");
String table = getTableName(uri);
if (table == null) {
throw new IllegalArgumentException("Unsupported URI: " + uri);
}
int row = mDb.update(table,values,selection,selectionArgs);
if (row > 0) {
getContext().getContentResolver().notifyChange(uri,null);
}
return row;
}
private String getTableName(Uri uri) {
String tableName = null;
if(uri.equals(URI))
tableName=DbOpenHelper.TABLE_NAME;
return tableName;
}
}
在MainActivity中訪問
Uri uri=Uri.parse("content://org.su.book.provider/book");
ContentResolver contentResolver=getContentResolver();
ContentValues values = new ContentValues();
values.put("_id",6);
values.put("name","程序設計");
values.put("author","c");
contentResolver.insert(uri,values);
Cursor bookCursor =contentResolver.query(uri,new String[]
{"_id","name","author"},null,null,null);
while (bookCursor.moveToNext()) {
int id= bookCursor.getInt(0);
String name = bookCursor.getString(1);
String author =bookCursor.getString(2);
Log.d(Tag,"query book:" +"id ="+id+",name ="+name+",author ="+author);
}
bookCursor.close();
日誌輸出：
四大組件初始之ContentProvider