ContentProvider的工作过程

ContentProvider是一种共享型组件，它通过Binder向其他组件或者其他应用程序提供数据，当ContentProvider所在进程启动时候，ContentProvider会被
同时启动并被发布到AMS中，需要注意的是：ContentProvider的onCreate要优先于Application的onCreate而执行。

ContentProvider的初始化过程

Application的创建

我们都知道当一个应用启动的时候，会最先执行ActivityThread#main方法、那么ContentProvider的初始化过程也一定是在这里进行的。

public static void main(String[] args) {     　　　...        Looper.prepareMainLooper();        ActivityThread thread = new ActivityThread();        //　attach方法中会初始化很多，比如绑定ContextImpl等        thread.attach(false);        if (sMainThreadHandler == null) {            sMainThreadHandler = thread.getHandler();        }        Looper.loop();}

ActivityThread#attach

private void attach(boolean system) {        if (!system) {            final IActivityManager mgr = ActivityManagerNative.getDefault();            try {                //　调用AMS的attachApplication，并且将ApplicationThread实例传递给AMS，ApplicationThread是一个Binder对象，主要用于ActivityThread和AMS通信                mgr.attachApplication(mAppThread);            } catch (RemoteException ex) {                // Ignore            }        } else {            try {                ContextImpl context = ContextImpl.createAppContext(                        this, getSystemContext().mPackageInfo);                mInitialApplication = context.mPackageInfo.makeApplication(true, null);                mInitialApplication.onCreate();            } catch (Exception e) {                throw new RuntimeException(                        "Unable to instantiate Application():" + e.toString(), e);            }        }　　　　　　　　....}

ActivityManagerService#attachApplication

@Overridepublic final void attachApplication(IApplicationThread thread) {        synchronized (this) {            int callingPid = Binder.getCallingPid();            final long origId = Binder.clearCallingIdentity();            //　调用了attachApplicationLocked传递ApplicationThread            attachApplicationLocked(thread, callingPid);            Binder.restoreCallingIdentity(origId);        }}

ActivityManagerService#attachApplicationLocked

private final boolean attachApplicationLocked(IApplicationThread thread,                                                  int pid) {        ....        try {　　　　　　　　　　　　// thread是一个ApplicationThread实例　　　　　　　　　　　　            thread.bindApplication(processName, appInfo, providers, app.instrumentationClass,                    profilerInfo, app.instrumentationArguments, app.instrumentationWatcher,                    app.instrumentationUiAutomationConnection, testMode, enableOpenGlTrace,                    isRestrictedBackupMode || !normalMode, app.persistent,                    new Configuration(mConfiguration), app.compat,                    getCommonServicesLocked(app.isolated),                    mCoreSettingsObserver.getCoreSettingsLocked());        } catch (Exception e) {        }        ....        return true;}

ApplicationThread#bindApplication

public final void bindApplication(String processName, ApplicationInfo appInfo,                List<ProviderInfo> providers, ComponentName instrumentationName,                ProfilerInfo profilerInfo, Bundle instrumentationArgs,                IInstrumentationWatcher instrumentationWatcher,                IUiAutomationConnection instrumentationUiConnection, int debugMode,                boolean enableOpenGlTrace, boolean isRestrictedBackupMode, boolean persistent,                Configuration config, CompatibilityInfo compatInfo, Map<String, IBinder> services,                Bundle coreSettings) {           　....            AppBindData data = new AppBindData();            data.processName = processName;            data.appInfo = appInfo;            data.providers = providers;            data.instrumentationName = instrumentationName;            data.instrumentationArgs = instrumentationArgs;            data.instrumentationWatcher = instrumentationWatcher;            data.instrumentationUiAutomationConnection = instrumentationUiConnection;            data.debugMode = debugMode;            data.enableOpenGlTrace = enableOpenGlTrace;            data.restrictedBackupMode = isRestrictedBackupMode;            data.persistent = persistent;            data.config = config;            data.compatInfo = compatInfo;            data.initProfilerInfo = profilerInfo;            //　发送BIND_APPLICATION消息，交给Ｈ处理            sendMessage(H.BIND_APPLICATION, data);}

H#handleMessage

case BIND_APPLICATION:     AppBindData data = (AppBindData)msg.obj;     handleBindApplication(data);     break;private void handleBindApplication(AppBindData data) {        ....        try {            //　创建Application            Application app = data.info.makeApplication(data.restrictedBackupMode, null);            mInitialApplication = app;            if (!data.restrictedBackupMode) {                List<ProviderInfo> providers = data.providers;                if (providers != null) {                    // 加载provider                    installContentProviders(app, providers);                }            }            try {                //　调用Application的onCreate                mInstrumentation.callApplicationOnCreate(app);            } catch (Exception e) {            }        } finally {            StrictMode.setThreadPolicy(savedPolicy);        }}

ContentProvider的初始化过程小结：

当一个应用启动的时候，会最先执行ActivityThread#main方法，在会最先执行main方法中会创建ActivityThread实例，并开启主线程的消息队列，
然后在ActivityThread#attach中会远程调用AMS中的attachApplication，并且将ApplicationThread实例传递给AMS，ApplicationThread是一个Binder对象，
主要用于ActivityThread和AMS通信，接着会回到ApplicationThread#bindApplication,接着交给Ｈ处理绑定application,在handleBindApplication中，
先创建Application，在加载provider，最后调用Application的onCreate，如下图：

ContentResolver访问数据源

我们可以通过ContentResolver来访问ContentProvider中提供的数据，ContentResolver是一个抽象类，我们可以通过Context的getContentResolver来获取，实际上
获取的是ApplicationContentResolver，ApplicationContentResolver继承自ContentResolver，当ContentProvider所在的进程没有启动的时候，第一次访问时候，
会触发ContentProvider的创建和其所在进程的启动，通过增删查改四个方法都可以触发，我们以query为栗子：

获取ContentResolver实现类

@Overridepublic ContentResolver getContentResolver() {　　　　　　　　// mContentResolver是ApplicationContentResolver的一个实例        return mContentResolver;}private static final class ApplicationContentResolver extends ContentResolver {        private final ActivityThread mMainThread;        private final UserHandle mUser;        public ApplicationContentResolver(                Context context, ActivityThread mainThread, UserHandle user) {            super(context);            mMainThread = Preconditions.checkNotNull(mainThread);            mUser = Preconditions.checkNotNull(user);        }        @Override        protected IContentProvider acquireProvider(Context context, String auth) {            return mMainThread.acquireProvider(context,                    ContentProvider.getAuthorityWithoutUserId(auth),                    resolveUserIdFromAuthority(auth), true);        }　　　　　　　　@Override        protected IContentProvider acquireUnstableProvider(Context c, String auth) {            return mMainThread.acquireProvider(c,                    ContentProvider.getAuthorityWithoutUserId(auth),                    resolveUserIdFromAuthority(auth), false);        }　　　　　　　　//释放当前Provider　　　　　　　　@Override        public boolean releaseProvider(IContentProvider provider) {            return mMainThread.releaseProvider(provider, true);        }　　　　　　　　@Override        public boolean releaseUnstableProvider(IContentProvider icp) {            return mMainThread.releaseProvider(icp, false);        }　　　　　....}

可以看到在ApplicationContentResolver中主要复写了父类ContentResolver中的acquireProvider和acquireUnstableProvider这两个方法，其实，当我们
执行”增删查改”任何一个操作时，最终都会由acquireUnstableProvider获取的IContentProvider实例执行。

调用query方法查询数据

public final @Nullable Cursor query(final @NonNull Uri uri, @Nullable String[] projection,            @Nullable String selection, @Nullable String[] selectionArgs,            @Nullable String sortOrder, @Nullable CancellationSignal cancellationSignal) {        IContentProvider unstableProvider = acquireUnstableProvider(uri);        if (unstableProvider == null) {            return null;        }        IContentProvider stableProvider = null;        Cursor qCursor = null;        try {            try {                //　通过unstableProvider执行查询操作                qCursor = unstableProvider.query(mPackageName, uri, projection,                        selection, selectionArgs, sortOrder, remoteCancellationSignal);            } catch (DeadObjectException e) {                // 远程进程死亡                unstableProviderDied(unstableProvider);　　　　　　　　　　　　　　　　// 当unstable死亡后，再创建stable类型的provider                stableProvider = acquireProvider(uri);                if (stableProvider == null) {                    return null;                }                //　再次执行查询操作                qCursor = stableProvider.query(mPackageName, uri, projection,                        selection, selectionArgs, sortOrder, remoteCancellationSignal);            }            if (qCursor == null) {                return null;            }            stableProvider = null;            qCursor = null;            return wrapper;        } catch (RemoteException e) {            return null;        } finally {　　　　　　　　　　　　//  释放资源            if (qCursor != null) {                qCursor.close();            }            if (cancellationSignal != null) {                cancellationSignal.setRemote(null);            }            if (unstableProvider != null) {                releaseUnstableProvider(unstableProvider);            }            if (stableProvider != null) {                releaseProvider(stableProvider);            }        }}

如上面所说，最终交给了ApplicationContentResolver中acquireUnstableProvider获取到的IContentProvider接口实例取执行具体的操作，所以接下来看下acquireUnstableProvider方法

@Overrideprotected IContentProvider acquireUnstableProvider(Context c, String auth) {　　　　　　　　// mMainThread是ActivityThread的实例        return mMainThread.acquireProvider(c,               ContentProvider.getAuthorityWithoutUserId(auth),               resolveUserIdFromAuthority(auth), false);}public final IContentProvider acquireProvider(            Context c, String auth, int userId, boolean stable) {        //　在ActivityThread中有一个mProviderMap的集合,每次会先从这里获取,如果不存在,则在创建对应的Provider并存入mProviderMap中        final IContentProvider provider = acquireExistingProvider(c, auth, userId, stable);        if (provider != null) {            return provider;        }        IActivityManager.ContentProviderHolder holder = null;        //　通过installProvider创建ContentProvider，并调用其onCreate方法        holder = installProvider(c, holder, holder.info,                true /*noisy*/, holder.noReleaseNeeded, stable);        return holder.provider;}

ActivityThread#installProvider

private IActivityManager.ContentProviderHolder installProvider(Context context,                                                                   IActivityManager.ContentProviderHolder holder, ProviderInfo info,                                                                   boolean noisy, boolean noReleaseNeeded, boolean stable) {        ContentProvider localProvider = null;        IContentProvider provider;        if (holder == null || holder.provider == null) {            //　创建对应包的Context对象            Context c = null;            ApplicationInfo ai = info.applicationInfo;            if (context.getPackageName().equals(ai.packageName)) {                c = context;            } else if (mInitialApplication != null &&                    mInitialApplication.getPackageName().equals(ai.packageName)) {                c = mInitialApplication;            } else {                try {                    c = context.createPackageContext(ai.packageName,                            Context.CONTEXT_INCLUDE_CODE);                } catch (PackageManager.NameNotFoundException e) {                    // Ignore                }            }            try {                //通过ClassLoader加载ContentProvider                final java.lang.ClassLoader cl = c.getClassLoader();                localProvider = (ContentProvider)cl.                        loadClass(info.name).newInstance();                provider = localProvider.getIContentProvider();                if (provider == null) {                    return null;                }                //　在ContentProvider.attachInfo方法中,会调用其onCreate方法                localProvider.attachInfo(c, info);            } catch (java.lang.Exception e) {                return null;            }        } else {            provider = holder.provider;        }        ....        // 在installProviderAuthoritiesLocked中会将当前providerf放入mProviderMap集合中        pr = installProviderAuthoritiesLocked(provider, localProvider, holder);        ....        return retHolder;}

上面　方法主要做了三件事情：
1. 创建对应包的Context对象
2. 通过ClassLoader加载ContentProvider,并执行attachInfo,在attachInfo中会执行当前provider的onCreate方法
3. 将当前provider放入mProviderMap集合中

到此为止，在代码中通过ContentResolver来访问操作数据时候，对应的ContentProvider也已经成功调用onCreate并且启动成功，并且ContentProvider所在进程的
Application也已经启动了。此时就可以通过AMS来访问该ContentProvider了，需要注意的是，该ContentProvider其实是一个Binder类型的对象IContentProvider,
在android系统中有一个抽象类ContentProviderNative实现了IContentProvider接口，其中ContentProvider的内部类Transport又继承自ContentProviderNative，所以
其他应用调用IContentProvider的query方法，最终会以进程间通信的方式调用到了ContentProvider$Transport的query方法.

自定义contentprovider

在Android开发中，有时需要在一个应用中调用操作系统中的另一个应用，而这个操作需要用到contentprovider，今天学习自定义的contentprovider，在android中contentprovider实际上是操作sqlite数据库来增删查改数据的，所以我们需要先写一个继承自SqliteOpenhelper的类，来创建数据库

MysqliteOpenhelper类

public class MySqliteOpenhelper extends SQLiteOpenHelper {    private String dbName = "people.db";    public MySqliteOpenhelper(Context context, String name,            CursorFactory factory, int version) {        super(context, name, null,1);    }    @Override    public void onCreate(SQLiteDatabase db) {        //创建userinfo表的sql语句        String sql = "create table userinfo(id int auto_increate,name varchar(30),age int,phone varchar(50))";        db.execSQL(sql);//创建表    }    @Override    public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2) {    }}

UserInfo实体类

public class UserInfo {      private int id;      private String name;      private String phone;      private int age;      public int getId() {          return id;      }      public void setId(int id) {          this.id = id;      }      public String getName() {          return name;      }      public void setName(String name) {          this.name = name;      }      public String getPhone() {          return phone;      }      public void setPhone(String phone) {          this.phone = phone;      }      public int getAge() {          return age;      }      public void setAge(int age) {          this.age = age;      }      public UserInfo(int id, String name, String phone, int age) {          super();          this.id = id;          this.name = name;          this.phone = phone;          this.age = age;      }      public UserInfo(String name, String phone, int age) {          super();          this.name = name;          this.phone = phone;          this.age = age;      }      @Override      public String toString() {          return "UserInfo [id=" + id + ", name=" + name + ", phone=" + phone                  + ", age=" + age + "]";      }  }

MyContentProvider类

创建需要向其他应用提供数据操作的contentprovider，MyContentProvider类

public class MyContentProvider extends ContentProvider {      private  UriMatcher uriMatcher;//声明需要封装uri的urimatcher      private  MySqliteOpenhelper helper;//声明创建数据库的helper      private static final int USERINFO = 1;      private static final int USERINFOS = 2;      @Override      public boolean onCreate() {          // TODO Auto-generated method stub          uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);          //添加uri          uriMatcher.addURI("com.test.self.provider","userinfo/#",USERINFO);//#是一个通配符          uriMatcher.addURI("com.test.self.provider","userinfos",USERINFOS);//整张表          helper = new MySqliteOpenhelper(getContext());          return true;      }      @Override      public int delete(Uri uri, String selection, String[] selectionArgs) {          // TODO Auto-generated method stub          SQLiteDatabase db = helper.getWritableDatabase();          int deleteNumber;          switch (uriMatcher.match(uri)) {          case USERINFOS://删除全部数据              deleteNumber = db.delete("userinfo",selection,selectionArgs);              return deleteNumber;          case USERINFO:              long id = ContentUris.parseId(uri);//解析得到需要删除的行的id              String where = "id="+id;              if (selection != null && !"".equals(selection)) {//如果有其他条件                  where = selection +" and "+where;              }              deleteNumber = db.delete("userinfo",where,selectionArgs);              return deleteNumber;          default:              throw new IllegalArgumentException("unknow uri:"+uri);          }      }      @Override      public String getType(Uri arg0) {          // TODO Auto-generated method stub          return null;      }      @Override      public Uri insert(Uri uri, ContentValues values) {          // TODO Auto-generated method stub          SQLiteDatabase db = helper.getWritableDatabase();          long insertId;          switch (uriMatcher.match(uri)) {          case USERINFOS:              insertId = db.insert("userinfo",null,values);//null表示每一列都插入              return ContentUris.withAppendedId(uri, insertId);//更新uri          default:              throw new IllegalArgumentException("unknow uri:"+uri);          }      }      @Override      public Cursor query(Uri uri, String[] projection, String where, String[] whereArgs,              String sortOrder) {          // TODO Auto-generated method stub          Cursor cursor;          SQLiteDatabase db = helper.getWritableDatabase();//得到创建好的db数据库          switch (uriMatcher.match(uri)) {          case USERINFO://content://com.test.self.provider/userinfo/4,,,,对id为4的userinfo查询操作              long id = ContentUris.parseId(uri);//解析得到id，即id=4              String wheres = "id="+id;              if (null != where && !"".equals(where)) {                  wheres = where +" and "+wheres;              }              cursor = db.query("userinfo",projection,wheres,whereArgs,null,null,sortOrder);              return cursor;          case USERINFOS://查询所有              cursor = db.query("userinfo",projection,where,whereArgs,null,null,sortOrder);              return cursor;          default:              throw new IllegalArgumentException("unknow uri:"+uri);          }      }      @Override      public int update(Uri uri, ContentValues values, String where, String[] whereArgs) {          // TODO Auto-generated method stub          SQLiteDatabase db = helper.getWritableDatabase();          int updateNumber;          switch (uriMatcher.match(uri)) {          case USERINFOS://更改所有数据              updateNumber = db.update("userinfo",values,where, whereArgs);              return updateNumber;          case USERINFO://更改一条数据              long id = ContentUris.parseId(uri);              String whereClause = "id="+id;              if (where != null && !"".equals(where)) {                  whereClause = where + " and "+whereClause;              }              updateNumber= db.update("userinfo", values, whereClause, whereArgs);              return updateNumber;          default:              throw new IllegalArgumentException("unknow uri:"+uri);          }      }  }

需要注意这里需要在清单文件里配置该provider

<provider             android:name="com.example.mycontentprovider.MyContentProvider"             android:authorities="com.test.self.provider"             android:exported="true"             >

调用contentprovider操作数据

public class MyClickListener implements OnClickListener {          Uri uri = null;          Cursor cursor;          @Override          public void onClick(View view) {              // TODO Auto-generated method stub              switch (view.getId()) {              case R.id.addone:                  uri = Uri.parse("content://com.test.self.provider/userinfos");                  ContentValues values = new ContentValues();                  values.put("name","wangwu");                  values.put("phone","264546");                  values.put("age", 20);                  getContentResolver().insert(uri, values);                  break;              case R.id.addAll:                  uri = Uri.parse("conent://com.test.self.provider/userinfos");                  for (int i = 0; i < 5; i++) {                      ContentValues values2 = new ContentValues();                      values2.put("name","zhangsan");                      values2.put("phone","264546");                      values2.put("age", 20);                      getContentResolver().insert(uri, values2);                  }              case R.id.deleteone:                  uri = Uri.parse("conent://com.test.self.provider/userinfo/3");//删除第三条数据                  getContentResolver().delete(uri, null, null);              case R.id.deleteall:                  uri = uri.parse("conent://com.test.self.provider/userinfos");                  getContentResolver().delete(uri, null, null);              case R.id.queryone:                  uri = Uri.parse("conent://com.test.self.provider/userinfo/6");//查询第六条数据                  cursor = getContentResolver().query(uri, null, null, null, null);                  if (cursor.moveToNext()) {                      int id = cursor.getInt(cursor.getColumnIndex("id"));                      String name = cursor.getString(cursor.getColumnIndex("name"));                      int age = cursor.getInt(cursor.getColumnIndex("age"));                      String phone = cursor.getString(cursor.getColumnIndex("phone"));                      System.out.println("id---"+id+"--name--"+name+"--age--"+age+"--phone--"+phone);                  }                  cursor.close();              case R.id.queryall:                  uri = Uri.parse("conent://com.test.self.provider/userinfos");                  cursor = getContentResolver().query(uri, null, null, null, null);                  while (cursor.moveToNext()) {                      int id = cursor.getInt(cursor.getColumnIndex("id"));                      String name = cursor.getString(cursor.getColumnIndex("name"));                      int age = cursor.getInt(cursor.getColumnIndex("age"));                      String phone = cursor.getString(cursor.getColumnIndex("phone"));                      System.out.println("id---"+id+"--name--"+name+"--age--"+age+"--phone--"+phone);                  }                  cursor.close();              case R.id.updateone:                  uri = Uri.parse("conent://com.test.self.provider/userinfo/6");                  ContentValues values3 = new ContentValues();                  values3.put("age",50);                  getContentResolver().update(uri, values3, null, null);              case R.id.updateall:                  uri = Uri.parse("conent://com.test.self.provider/userinfos");                  ContentValues values4 = new ContentValues();                  values4.put("name","lisi");                  getContentResolver().update(uri, values4, null,null);              default:                  break;              }          }