Android(安卓)基础总结：（十一）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.javafroyo/frameworks/base/core/java/android/app/ActivityThread.javafroyo/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.

我们来看看效果图：

由于黑色的继承关系，我们可以得到红色的调用关系我们看看效果图就知道了，它们两个是怎么样跳过文件来直接联系在一起的。这样的话我们就省去了很多环节，也给我们节省了时间这样的话我们也不容易出错，这样以来我们就会大大的提高了我们的工作效率，

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;}

Java代码：

mContentResolve r = new ApplicationContentResolver(this, mainThread);private static final class ApplicationContentResolver extendsContentResolver {public ApplicationContentResolver(Context context,ActivityThread mainThread) {super(context);mMainThread = mainThread;}@Overrideprotected IContentProvider acquireProvider(Context context, String name) {return mMainThread.acquireProvider(context, name);}@Overridepublic 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;}// CursorWrapperInner光标对象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);

Java代码：

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 synchronizedreturn 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// 供应商,不在乎被释放,或如果它是// 本地提供运行这一过程。// Log.i(TAG, "*** NO RELEASE NEEDED");synchronized (mProviderMap) {mProviderRefCountMap.put(prov.asBinder(), new ProviderRefCount(10000));}}return prov;}

上面的代码if(provider==null)后面有一个返回值，这个返回值一定要是空，不要写别的，后面的判断我们也都判断为空，这样我们就完成了contentResolver与contentProvider联系在一起了。

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