Android contentResolver与contentProvider如何关联在一起的

Application是一个完整的应用，比如某个apk,它对应一个Application,它里面可能包含n个Activity。

涉及到的类froyo/frameworks/base/core/java/android/app/ApplicationContext.java

froyo/frameworks/base/core/java/android/app/ActivityThread.java

froyo/frameworks/base/services/java/com/android/server/am/ActivityManagerService.java

当我们启动手机之后，如果需要启动一个activity,ActivityThread,ActivityManagerService就开始发挥作用了,这里不做细述。

当我们真正的启动一个activity的时候，我们会把当前Application的ApplicationContext传进去，

ApplicationContext实例持有一个mContextResolver对象，该对象对应于ApplicationContext的

内部类ApplicationContentResolver.

当activity调用getContentResolver()时，我们实际调用的是当前ApplicationContext中的mContextResolver.

由于黑色的继承关系，我们可以得到红色的调用关系

代码片段如下：
Activity调用ContextWrapper的方法

getContentResolver() {   mBase.getContentResolver();   }

然后会调用到ApplicationContext的方法

getContentResolver() {   return mContentResolver;   }

其中：

mContentResolve r = new ApplicationContentResolver(this, mainThread);   private static final class ApplicationContentResolver extends ContentResolver { public ApplicationContentResolver(Context context, ActivityThread mainThread) { super(context); mMainThread = mainThread; }   @Override protected IContentProvider acquireProvider(Context context, String name) { return mMainThread.acquireProvider (context, name); }   @Override public boolean releaseProvider(IContentProvider provider) { return mMainThread.releaseProvider(provider); }   private final ActivityThread mMainThread; }

当执行mContentResolver.query()的时候，我们会调用父类ContentResolver的query();

public final Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) { IContentProvider provider = acquireProvider(uri); if (provider == null) { return null; } try { Cursor qCursor = provider.query(uri, projection, selection, selectionArgs, sortOrder); if(qCursor == null) { releaseProvider(provider); return null; } //Wrap the cursor object into CursorWrapperInner object return new CursorWrapperInner(qCursor, provider); } catch (RemoteException e) { releaseProvider(provider); return null; } catch(RuntimeException e) { releaseProvider(provider); throw e; } }   public final IContentProvider acquireProvider(Uri uri) { if (!SCHEME_CONTENT.equals(uri.getScheme())) { return null; } String auth = uri.getAuthority(); if (auth != null) { return acquireProvider(mContext, uri.getAuthority()); } return null; }

此时，会调用子类实例aquireProvider(Context,name);

mMainThread.acquireProvider (context, name);

实现为：

public final IContentProvider acquireProvider (Context c, String name) { IContentProvider provider = getProvider (c, name); if(provider == null) return null; IBinder jBinder = provider.asBinder(); //获得binder对象，跨进程传递数据。 synchronized(mProviderMap) { ProviderRefCount prc = mProviderRefCountMap.get(jBinder); if(prc == null) { mProviderRefCountMap.put(jBinder, new ProviderRefCount(1)); } else { prc.count++; } //end else } //end synchronized return provider; }   private final IContentProvider getProvider (Context context, String name) { synchronized(mProviderMap) { final ProviderRecord pr = mProviderMap .get(name); //ActivityThread中持有所有的Provider的实例 if (pr != null) { return pr.mProvider; } } //如果确实没有，则查找，并install，再没有就直接抛异常了。 IActivityManager.ContentProviderHolder holder = null; try { holder = ActivityManagerNative.getDefault().getContentProvider( getApplicationThread(), name); } catch (RemoteException ex) { } if (holder == null) { Log.e(TAG, "Failed to find provider info for " + name); return null; } if (holder.permissionFailure != null) { throw new SecurityException("Permission " + holder.permissionFailure + " required for provider " + name); }   IContentProvider prov = installProvider(context, holder.provider, holder.info, true); //Log.i(TAG, "noReleaseNeeded=" + holder.noReleaseNeeded); if (holder.noReleaseNeeded || holder.provider == null) { // We are not going to release the provider if it is an external // provider that doesn't care about being released, or if it is // a local provider running in this process. //Log.i(TAG, "*** NO RELEASE NEEDED"); synchronized(mProviderMap) { mProviderRefCountMap.put(prov.asBinder(), new ProviderRefCount(10000)); } } return prov; }

到这里的话，ContentResovler与ContentProvider的关系就搞懂了，具体其他的细节，将分为不同的方面，分别讲述。

原文链接：http://blog.csdn.net/yangxinle137/archive/2010/11/03/5985608.aspx