好了，终于到了最后一个啦，写到这里，真的觉得不容意啊，以前看这些组件也就那样了，现在还要记录下来，重点是这东西都被分析烂了，我们这些后人屌丝还在写，没点突破的。真没意思呢！就当写作业咯。啦啦啦啦，不管如何，让我们开始看下吧
起航 — ContentResolver
API： 23
说真的，这个组件我还真的相对于Activity和Service用起来真的好少啊！
现在都不能记起来用他来干嘛了，虽然知道他能用来做跨进程通讯用，不过对于一般的app。
这玩意还真的用的次数少啊! 现在能想起来的一次使用这个就是要获取图片的时候。
以前开发的时候遇到的恶心的是，有些Rom把相册给阉割了，搞了个别的来代替，导致调不了图库！
所以搞到需要自己开发一个，真的很无语！
ContentResolver mContentResolver = this.getContentResolver();
Cursor mCursor = mContentResolver.query(mImageUri, null,
MediaStore.Images.Media.MIME_TYPE + "=? or "
+ MediaStore.Images.Media.MIME_TYPE + "=? or " + MediaStore.Images.Media.MIME_TYPE + "=?" + " or " + MediaStore.Images.Media.MIME_TYPE + "=?",
new String[]{"image/jpeg", "image/png", "image/jpg", "image/jpe"},
MediaStore.Images.Media.DATA);
从这里我们开始看起吧
public final Cursor query(Uri uri, String[] projection,
String selection, String[] selectionArgs, String sortOrder) {
return query(uri, projection, selection, selectionArgs, sortOrder, null);
}
public final Cursor query(final Uri uri, String[] projection,
String selection, String[] selectionArgs, String sortOrder,
CancellationSignal cancellationSignal) {
IContentProvider unstableProvider = acquireUnstableProvider(uri);
if (unstableProvider == null) {
return null;
}
IContentProvider stableProvider = null;
Cursor qCursor = null;
try {
...
ICancellationSignal remoteCancellationSignal = null;
if (cancellationSignal != null) {
cancellationSignal.throwIfCanceled();
remoteCancellationSignal = unstableProvider.createCancellationSignal();
cancellationSignal.setRemote(remoteCancellationSignal);
}
try {
qCursor = unstableProvider.query(mPackageName, uri, projection,
selection, selectionArgs, sortOrder, remoteCancellationSignal);
} catch (DeadObjectException e) {
unstableProviderDied(unstableProvider);
stableProvider = acquireProvider(uri);
if (stableProvider == null) {
return null;
}
qCursor = stableProvider.query(mPackageName, uri, projection,
selection, selectionArgs, sortOrder, remoteCancellationSignal);
}
if (qCursor == null) {
return null;
}
// Force query execution. Might fail and throw a runtime exception here.
qCursor.getCount();
long durationMillis = SystemClock.uptimeMillis() - startTime;
maybeLogQueryToEventLog(durationMillis, uri, projection, selection, sortOrder);
// Wrap the cursor object into CursorWrapperInner object.
CursorWrapperInner wrapper = new CursorWrapperInner(qCursor,
stableProvider != null ? stableProvider : acquireProvider(uri));
stableProvider = null;
qCursor = null;
return wrapper;
} catch (RemoteException e) {
return null;
} finally {
...
}
}
@Override
protected IContentProvider acquireUnstableProvider(Context c, String auth) {
return mMainThread.acquireProvider(c,
ContentProvider.getAuthorityWithoutUserId(auth),
resolveUserIdFromAuthority(auth), false);
}
开头调用acquireUnstableProvider(uri)，经过一轮跟踪，发现他跑到了ActivityThread里面的acquireProvider，内容如下
public final IContentProvider acquireProvider(
Context c, String auth, int userId, boolean stable) {
final IContentProvider provider = acquireExistingProvider(c, auth, userId, stable);
if (provider != null) {
return provider;
}
IActivityManager.ContentProviderHolder holder = null;
try {
holder = ActivityManagerNative.getDefault().getContentProvider(
getApplicationThread(), auth, userId, stable);
} catch (RemoteException ex) {
}
if (holder == null) {
return null;
}
// Install provider will increment the reference count for us, and break
// any ties in the race.
holder = installProvider(c, holder, holder.info,
true /*noisy*/, holder.noReleaseNeeded, stable);
return holder.provider;
}
我们看到他先查找本地有没有，有就返回，没有就去找了AMS要ContentProvider，拿回来后就存本地，然后返回。
好了，让我们去看下AMS里面的实现吧
@Override
public final ContentProviderHolder getContentProvider(
IApplicationThread caller, String name, int userId, boolean stable) {
enforceNotIsolatedCaller("getContentProvider");
if (caller == null) {
String msg = "null IApplicationThread when getting content provider "
+ name;
Slog.w(TAG, msg);
throw new SecurityException(msg);
}
return getContentProviderImpl(caller, name, null, stable, userId);
}
他跑去了他的实现函数getContentProviderImpl(）….真无语，同个类里面还搞抽象和实现啊，
像前面那样写成realGetContentProviderImpl(）不就好了嘛，哈哈，真 · 干活函数
不过这个实现还不小，三百多行，这在AMS里面都是这样的，看着头疼，一堆的判断，截取关键的部分：
private final ContentProviderHolder getContentProviderImpl(IApplicationThread caller,
String name, IBinder token, boolean stable, int userId) {
ContentProviderRecord cpr;
ContentProviderConnection conn = null;
ProviderInfo cpi = null;
...
proc = startProcessLocked(cpi.processName,
cpr.appInfo, false, 0, "content provider",
new ComponentName(cpi.applicationInfo.packageName,
cpi.name), false, false, false);
cpr.launchingApp = proc;
mLaunchingProviders.add(cpr);
mProviderMap.putProviderByName(name, cpr);
conn = incProviderCountLocked(r, cpr, token, stable);
return cpr != null ? cpr.newHolder(conn) : null;
}
这里需要补充的说明是，我们都知道那个ContentProvider的启动是伴随进程的启动，启动进程是有上面的startProcessLocked(）来完成的。我们来看下他里面写了什么。。。
private final void startProcessLocked(ProcessRecord app, String hostingType,
String hostingNameStr, String abiOverride, String entryPoint, String[] entryPointArgs) {
...
checkTime(startTime, "startProcess: asking zygote to start proc");
Process.ProcessStartResult startResult = Process.start(entryPoint,
app.processName, uid, uid, gids, debugFlags, mountExternal,
app.info.targetSdkVersion, app.info.seinfo, requiredAbi, instructionSet,
app.info.dataDir, entryPointArgs);
checkTime(startTime, "startProcess: returned from zygote!");
...
}
这个函数也是一个巨无霸，我想那个AMS一定是靠几个人写完的，因为他的函数风格不在一样，呵呵，虽然我也经常写得不一样。只截取重要的几句..
这个函数最终通过调用Process的start方法来启动。我们继续深入看下
public static final ProcessStartResult start(final String processClass,
final String niceName,
int uid, int gid, int[] gids,
int debugFlags, int mountExternal,
int targetSdkVersion,
String seInfo,
String abi,
String instructionSet,
String appDataDir,
String[] zygoteArgs) {
try {
return startViaZygote(processClass, niceName, uid, gid, gids,
debugFlags, mountExternal, targetSdkVersion, seInfo,
abi, instructionSet, appDataDir, zygoteArgs);
} catch (ZygoteStartFailedEx ex) {
Log.e(LOG_TAG,
"Starting VM process through Zygote failed");
throw new RuntimeException(
"Starting VM process through Zygote failed", ex);
}
}
好，遇到了一个传说级别的名字了Zygote，不要问我这个名词代表的故事，百度下吧。
感觉写完这些组件后，可以开始写更底层的部分了…哎。说真的，挺无聊的，看完又没怎么样，但出来混，他们老觉得高级开发就得看底层代码，精通整个Android系统啊！这学习量真的不小，不过也就那点工资…
还不如学校门口一个摆摊的，好了，罗嗦了，继续吧。
结论就是通过Zygote,最后我们到了ActivityThread的main方法，还记得这个玩意嘛？
我们在很久前解析那个Handler的时候有提到，程序的入口方法是ActivityThread的mian方法！
是不是觉得很像以前学java时候！居然在安卓里面遇到人家！
public static void main(String[] args) {
SamplingProfilerIntegration.start();
...
Looper.prepareMainLooper();
ActivityThread thread = new ActivityThread();
thread.attach(false);
if (sMainThreadHandler == null) {
sMainThreadHandler = thread.getHandler();
}
AsyncTask.init();
if (false) {
Looper.myLooper().setMessageLogging(new
LogPrinter(Log.DEBUG, "ActivityThread"));
}
Looper.loop();
throw new RuntimeException("Main thread loop unexpectedly exited");
}
整个的main方法就初始主线程的地方，同时开动主Looper， 然后attach这个方法会最终把消息传递AMS，然后AMS就完成了ContentProvider的创建！
private void attach(boolean system) {
...
try {
mgr.attachApplication(mAppThread);
} catch (RemoteException ex) {
// Ignore
}
...
}
private final boolean attachApplicationLocked(IApplicationThread thread,
int pid) {
// Find the application record that is being attached... either via
// the pid if we are running in multiple processes, or just pull the
// next app record if we are emulating process with anonymous threads.
ProcessRecord app;
...
if (DEBUG_CONFIGURATION) Slog.v(TAG, "Binding proc "
+ processName + " with config " + mConfiguration);
ApplicationInfo appInfo = app.instrumentationInfo != null
? app.instrumentationInfo : app.info;
app.compat = compatibilityInfoForPackageLocked(appInfo);
if (profileFd != null) {
profileFd = profileFd.dup();
}
ProfilerInfo profilerInfo = profileFile == null ? null
: new ProfilerInfo(profileFile, profileFd, samplingInterval, profileAutoStop);
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(),
mCoreSettingsObserver.getCoreSettingsLocked());
updateLruProcessLocked(app, false, null);
app.lastRequestedGc = app.lastLowMemory = SystemClock.uptimeMillis();
...
}
每次到AMS里面的函数都是一大串！！！这里的thread就是那个ApplicationThread，我们很熟悉。
走了一圈，又跑回来了
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;
sendMessage(H.BIND_APPLICATION, data);
}
最终这个变成了同我们的H先生发送BIND_APPLICATION消息！
private void handleBindApplication(AppBindData data) {
...
// 1.创建Context
ContextImpl instrContext = ContextImpl.createAppContext(this, pi);
java.lang.ClassLoader cl = instrContext.getClassLoader();
mInstrumentation = (Instrumentation)
cl.loadClass(data.instrumentationName.getClassName()).newInstance();
mInstrumentation.init(this, instrContext, appContext,
new ComponentName(ii.packageName, ii.name), data.instrumentationWatcher,
data.instrumentationUiAutomationConnection);
...
// 2.创建app
Application app = data.info.makeApplication(data.restrictedBackupMode, null);
mInitialApplication = app;
...
// 3. 启动ContentProvider，发送消息，调用onCreate函数
// don't bring up providers in restricted mode; they may depend on the
// app's custom Application class
if (!data.restrictedBackupMode) {
List<ProviderInfo> providers = data.providers;
if (providers != null) {
installContentProviders(app, providers);
// For process that contains content providers, we want to
// ensure that the JIT is enabled "at some point".
mH.sendEmptyMessageDelayed(H.ENABLE_JIT, 10*1000);
}
}
...
//4. 启动我们Application的onCreate方法。
// Do this after providers, since instrumentation tests generally start their
// test thread at this point, and we don't want that racing.
mInstrumentation.onCreate(data.instrumentationArgs);
mInstrumentation.callApplicationOnCreate(app);
StrictMode.setThreadPolicy(savedPolicy);
}
这个函数受AMS污染，也是贼长的一个函数。
在这个handleBindApplication函数里面，我截取保留了核心的信息，同时加了注释。
具体就是创建context和Application，然后通过installContentProviders(）来启动当前进程的ContentProvider，所以下次有人和你提问题，说你知道那个ContentProvider嘛？
你就反问，说你知道这个组件是在哪里初始化的嘛？
不知道你就说是在ActivityThread里面的H先生接受到了BindApplication消息，然后在处理消息对应的handleBindApplication（）方法里面的installContentProviders(）函数啦！
是不是很装逼的样子！！
为了彻底的装逼，我们来看下这个installContentProviders(）到底做了什么！
免得人家也看过代码，惨遭装逼失败的下场。
private void installContentProviders(
Context context, List<ProviderInfo> providers) {
final ArrayList<IActivityManager.ContentProviderHolder> results =
new ArrayList<IActivityManager.ContentProviderHolder>();
for (ProviderInfo cpi : providers) {
IActivityManager.ContentProviderHolder cph = installProvider(context, null, cpi,
false /*noisy*/, true /*noReleaseNeeded*/, true /*stable*/);
if (cph != null) {
cph.noReleaseNeeded = true;
results.add(cph);
}
}
try {
ActivityManagerNative.getDefault().publishContentProviders(
getApplicationThread(), results);
} catch (RemoteException ex) {
}
}
这里面遍历了providers，然后installProvider去启动他们。最后找AMS把他们给注册保存了。
而且是保存在一个叫mProviderMap的map里面中，便于别的进程通过AMS来调用！
有代码有真相，有木有，就在下面，没骗人的啊！
public final void publishContentProviders(IApplicationThread caller,
List<ContentProviderHolder> providers) {
...
enforceNotIsolatedCaller("publishContentProviders");
synchronized (this) {
final ProcessRecord r = getRecordForAppLocked(caller);
final long origId = Binder.clearCallingIdentity();
final int N = providers.size();
for (int i=0; i<N; i++) {
ContentProviderHolder src = providers.get(i);
...
ContentProviderRecord dst = r.pubProviders.get(src.info.name);
if (dst != null) {
ComponentName comp = new ComponentName(dst.info.packageName, dst.info.name);
mProviderMap.putProviderByClass(comp, dst);
String names[] = dst.info.authority.split(";");
for (int j = 0; j < names.length; j++) {
mProviderMap.putProviderByName(names[j], dst);
}
...
updateOomAdjLocked(r);
}
}
Binder.restoreCallingIdentity(origId);
}
}
在彻底的装逼，我们需要来看下这个installProvider函数
private IActivityManager.ContentProviderHolder installProvider(Context context,
IActivityManager.ContentProviderHolder holder, ProviderInfo info,
boolean noisy, boolean noReleaseNeeded, boolean stable) {
ContentProvider localProvider = null;
IContentProvider provider;
...
try { //用ClassLoader去加载！
final java.lang.ClassLoader cl = c.getClassLoader();
localProvider = (ContentProvider)cl.
loadClass(info.name).newInstance();
provider = localProvider.getIContentProvider();
...
// XXX Need to create the correct context for this provider.
localProvider.attachInfo(c, info);
} catch (java.lang.Exception e) {
...
}
return null;
}
}
...
}
好了他的启动过程基本到这里结束，我们回溯到前面的步骤，回到我们处理Application消息的第四点
//4. 启动我们Application的onCreate方法。
// Do this after providers, since instrumentation tests generally start their
// test thread at this point, and we don't want that racing.
mInstrumentation.onCreate(data.instrumentationArgs);
mInstrumentation.callApplicationOnCreate(app);
StrictMode.setThreadPolicy(savedPolicy);
好了，整个过程基本这样了。
我们从一开始的acquireUnstableProvider(uri);函数跑到这里，都快忘记原本是要干嘛了。
续航 ==== Query
让我们继续启程，回到一开始query函数，在获得了我们IContentProvider后，就调用了他的query方法。
qCursor = unstableProvider.query(mPackageName, uri, projection,
selection, selectionArgs, sortOrder, remoteCancellationSignal);
这个IContentProvider 是一个Binder接口，具体的干活的人是谁呢？IContentProvider的具体实现是ContentProviderNative，然后Transport 又继承了它。
abstract public class ContentProviderNative extends Binder implements IContentProvider
class Transport extends ContentProviderNative
这个类是躲在ContentProvider的里面的即ContentProvider.Transport 。好了，写了这么多，回主线
@Override
public Cursor query(String callingPkg, Uri uri, String[] projection,
String selection, String[] selectionArgs, String sortOrder,
ICancellationSignal cancellationSignal) {
validateIncomingUri(uri);
uri = getUriWithoutUserId(uri);
if (enforceReadPermission(callingPkg, uri, null) != AppOpsManager.MODE_ALLOWED) {
...
Cursor cursor = ContentProvider.this.query(uri, projection, selection,
selectionArgs, sortOrder, CancellationSignal.fromTransport(
cancellationSignal));
if (cursor == null) {
return null;
}
// Return an empty cursor for all columns.
return new MatrixCursor(cursor.getColumnNames(), 0);
}
final String original = setCallingPackage(callingPkg);
try {
return ContentProvider.this.query(
uri, projection, selection, selectionArgs, sortOrder,
CancellationSignal.fromTransport(cancellationSignal));
} finally {
setCallingPackage(original);
}
}
到这里去调用了ContentProvider的query方法。这样整个过程就结束了。其余的方法也在这个类里面，套路类似的，就不再写了，这篇文章已经写了很长了，而且现在有事，得去做点别了！
后记
今天写得好晚，看到都有点累，不段的翻滚。。。写到后面都没精神和注意力了。。
先写到这里，洗个澡睡觉，明天抽时间在继续做补充。。
但无论如何把四大金刚的源码都写了一遍了。
====
更新：
重新补充了部分内容，把整个流程更细化了下。
不过还是有些具体的内容不是很清楚，
下一次在游览别的时候，能有空再把这个过程写得更清楚的话，就再来更新吧
对于Zygote这个下次得抽时间再写一篇他的专辑。
谷歌起这个名字给它，这么有深度东西，很有故事。
下一篇就这么定是他了 ^_ ^