Android播音发送机制剖析【android广播系列二】

   上篇博客大致说了说广播的注册机制，动态注册和静态注册广播的原理还不一样，动态广播最后HashMap中了，最后放到mReceiverResolver中，以后当ActivityManagerService接收到广播的时候，它就可以再成员变量mReceiverResolver中找到对应的广播接收者了。下面我们来说说广播的发送机制。
   广播发送时候，在Context.java的方法中调用的，有如下方法：
   sendBroadcast(Intent intent) ；
   sendBroadcast(Intent intent, String receiverPermission) 
   sendBroadcastAsUser(Intent intent, UserHandle user) 
   sendBroadcastAsUser(Intent intent, UserHandle user, String receiverPermission)
   sendOrderedBroadcast(Intent intent, String receiverPermission)
   sendOrderedBroadcastAsUser(Intent intent, UserHandle user, String receiverPermission, BroadcastReceiver resultReceiver, Handler scheduler, int initialCode, String initialData, Bundle initialExtras) 
   sendStickyBroadcast(Intent intent) 
   sendStickyBroadcastAsUser(Intent intent, UserHandle user) 
   sendStickyOrderedBroadcast(Intent intent, BroadcastReceiver resultReceiver, Handler scheduler, int initialCode, String initialData, Bundle initialExtras) 
   sendStickyOrderedBroadcastAsUser(Intent intent, UserHandle user, BroadcastReceiver resultReceiver, Handler scheduler, int initialCode, String initialData, Bundle initialExtras) 
  以上就是发送广播的方式，但是常用的就几种，其中比较常用的就是sendBroadcast(Intent intent) ；我就说下这种发送广播的方式。

Step1：

sendBroadcast在context中调用的，往下调用到了ContextImpl.java中去了：

/**
 * Common implementation of Context API, which provides the base
 * context object for Activity and other application components.
 */
class ContextImpl extends Context {
    private final static String TAG = "ContextImpl";
    private final static boolean DEBUG = false;

@Override
public void sendBroadcast(Intent intent, String receiverPermission) {
        warnIfCallingFromSystemProcess();
        String resolvedType = intent.resolveTypeIfNeeded(getContentResolver());
        try {
            intent.prepareToLeaveProcess();
            ActivityManagerNative.getDefault().broadcastIntent(
                mMainThread.getApplicationThread(), intent, resolvedType, null,
                Activity.RESULT_OK, null, null, receiverPermission, AppOpsManager.OP_NONE,
                false, false, getUserId());
        } catch (RemoteException e) {
        }
    }

Step2：

调用到了ActivityManagerService.java中的broadcastIntent（）方法中去了，

public final int broadcastIntent(IApplicationThread caller,
            Intent intent, String resolvedType, IIntentReceiver resultTo,int resultCode, String resultData, Bundle map, String requiredPermission, int appOp, boolean serialized, boolean sticky, int userId) {
        enforceNotIsolatedCaller("broadcastIntent");
        synchronized(this) {
        //校验广播是否锁定
            intent = verifyBroadcastLocked(intent);

            final ProcessRecord callerApp = getRecordForAppLocked(caller);
            final int callingPid = Binder.getCallingPid();
            final int callingUid = Binder.getCallingUid();
            final long origId = Binder.clearCallingIdentity();
            int res = broadcastIntentLocked(callerApp,
                    callerApp != null ? callerApp.info.packageName : null,
                    intent, resolvedType, resultTo,
                    resultCode, resultData, map, requiredPermission, appOp, serialized, sticky,
                    callingPid, callingUid, userId);
            Binder.restoreCallingIdentity(origId);
            return res;
        }
    }