从Android源码剖析Intent查询匹配的实现

时间:2022-05-11 21:30:52

前言
    这篇文章主要是介绍一下Android Intent,并且从Android源码的角度对Intent查询匹配过程进行分析。

Intent介绍
    Intent的中文是“意图”的意思,而意图是一个非常抽象的概念,那么在Android的编码设计中,如何实例化意图呢?因此Android系统明确指定一个Intent可由两方面属性来衡量。

    主要属性:包括Action和Data。其中Action用于表示该Intent所表达的动作意图,Data用于表示该Action所操作的数据。
    次要属性:包括Category、Type、Component和Extras。其中Category表示类别,Type表示数据的MIME类型,Component可用于指定特定的Intent的响应者(例如指定intent为某个包下的某个class类),Extras用于承载其他的信息。

    Android系统中主要有两种类型的Intent,显示Intent(Explicit Intent)和隐式Intent(Implicit Intent)。

    Explicit Intent:这类Intent明确指明了要找哪个Component。在代码中可以通过setClassName或者setComponent来锁定目标对象。
    Implicit Intent:这类Intent不明确指明要启动哪个Component,而是设置Action、Data、Category让系统来筛选出合适的Component。

    接下来,写两个代码示例,来介绍一下Explicit Intent和Implict Inent。首先是Explicit Intent:

   

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private void startExplicitIntentWithComponent() {
   Intent intent = new Intent();
   ComponentName component = new ComponentName("com.example.photocrop", "com.example.photocrop.MainActivity");
   intent.setComponent(component);
   startActivity(intent);
 }
  
 private void startExplicitIntentWithClassName() {
   Intent intent = new Intent();
   intent.setClassName("com.example.photocrop", "com.example.photocrop.MainActivity");
   startActivity(intent);
 }

    但是,从源码里面去看,发现setClassName也是借助了ComponentName实现了Explicit Intent。源码如下:

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public Intent setClassName(String packageName, String className) {
  mComponent = new ComponentName(packageName, className);
  return this;
}

    然后,在给出一个Implict Intent的代码示例。我这里用一个Activity标注一些Intent Filter为例,然后在写一个Intent用于启动它。

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<activity 
  android:name=".SendIntentType">
  <intent-filter >
    <action android:name="justtest"/>
    <category android:name="justcategory"/>
  </intent-filter>
</activity>

    在当前应用的AndroidManifest.xml中,给SendIntentType类增加了intent-filter,action的名字为“justtest”,category的名字为“justcategory”。启动该Activity的代码如下:

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private void startImplictIntent() {
  Intent intent = new Intent();
  intent.setAction("justaction");
  intent.addCategory("justcategory");
  startActivity(intent);
}

    系统在匹配Implict Intent的过程中,将以Intent Filter列出的3项内容为参考标准,具体步骤如下:

  •     首先匹配IntentFilter的Action,如果Intent设置的action不满足IntentFilter的Action,则匹配失败。如果IntentFilter未设定Action或者设定的Action相同,则匹配成功。
  •     然后检查IntentFilter的Category,匹配方法同Action的匹配相同,唯一例外的是当Category为CATEGORY_DEFAULT的情况。
  •     最后检查Data。


Activityi信息的管理
    从上面的分析可以看出,系统的匹配Intent的过程中,首先需要管理当前系统中所有Activity信息。Activity的信息是PackageManagerService在扫描APK的时候进行收集和管理的。相关源码如下:

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// 处理该package的activity信息
N = pkg.activities.size();
r = null;
for (i = 0; i < N; i++) {
  PackageParser.Activity a = pkg.activities.get(i);
  a.info.processName = fixProcessName(pkg.applicationInfo.processName, a.info.processName,
      pkg.applicationInfo.uid);
  mActivities.addActivity(a, "activity");
}

    上面代码中,有两个比较重要的数据结构,如下图所示。

从Android源码剖析Intent查询匹配的实现

结合代码和上图的数据结构,可知:

    mAcitivitys为ActivityIntentResolver类型,是PKMS的成员变量,用于保存系统中所有与Activity相关的信息。此数据结构内部也有一个mActivities变量,它以ComponentName为key,保存PackageParser.Activity对象。
    从APK中解析得到的所有和Acitivity相关的信息(包括XML中声明的IntentFilter标签)都由PackageParser.Activity来保存。

    前面代码中调用addActivity函数完成了私有信息的公有化。addActivity函数的代码如下:

    

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public final void addActivity(PackageParser.Activity a, String type) {
    final boolean systemApp = isSystemApp(a.info.applicationInfo);
    mActivities.put(a.getComponentName(), a);
    final int NI = a.intents.size();
    for (int j = 0; j < NI; j++) {
      PackageParser.ActivityIntentInfo intent = a.intents.get(j);
      if (!systemApp && intent.getPriority() > 0 && "activity".equals(type)) {
        // 非系统APK的priority必须为0
        intent.setPriority(0);
      }
      addFilter(intent);
    }
  }

    接下来看一下addFilter函数。函数源码如下:

  

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public void addFilter(F f) {
   // mFilters保存所有IntentFilter信息
   mFilters.add(f);
   int numS = register_intent_filter(f, f.schemesIterator(),
       mSchemeToFilter, "   Scheme: ");
   int numT = register_mime_types(f, "   Type: ");
   if (numS == 0 && numT == 0) {
     register_intent_filter(f, f.actionsIterator(),
         mActionToFilter, "   Action: ");
   }
   if (numT != 0) {
     register_intent_filter(f, f.actionsIterator(),
         mTypedActionToFilter, "   TypedAction: ");
   }
 }

    这里又出现了几种数据结构,它们的类似都是ArrayMap<String, F[ ]>,其中F为模板参数。

  •     mSchemeToFilter:用于保存uri中与scheme相关的IntentFilter信息。
  •     mActionToFilter:用于保存仅设置Action条件的IntentFilter信息。
  •     mTypedActionToFilter:用于保存既设置了Action又设置了Data的MIME类型的IntentFilter信息。

    了解了大概的数据结构之后,我们来看一下register_intent_filter的函数实现:

  

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private final int register_intent_filter(F filter, Iterator<String> i,
     ArrayMap<String, F[]> dest, String prefix) {
   if (i == null) {
     return 0;
   }
  
   int num = 0;
   while (i.hasNext()) {
     String name = i.next();
     num++;
     addFilter(dest, name, filter);
   }
   return num;
 }

    然后又是一个addFilter函数,明显是一个函数重载,我们来看一下这个addFilter的实现:

    

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private final void addFilter(ArrayMap<String, F[]> map, String name, F filter) {
    F[] array = map.get(name);
    if (array == null) {
      array = newArray(2);
      map.put(name, array);
      array[0] = filter;
    } else {
      final int N = array.length;
      int i = N;
      while (i > 0 && array[i-1] == null) {
        i--;
      }
      if (i < N) {
        array[i] = filter;
      } else {
        F[] newa = newArray((N*3)/2);
        System.arraycopy(array, 0, newa, 0, N);
        newa[N] = filter;
        map.put(name, newa);
      }
    }
  }

    其实代码还是很简单的,如果F数组存在,则判断容量,不够则扩容,够的话就找到位置插入。如果F数组不存在,则创建一个容量为2的数组,将0号元素赋值为该filter。

Intent匹配查询分析
    客户端通过ApplicationPackageManager输出的queryIntentActivities函数向PackageManagerService发起一次查询请求,代码如下:

  

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@Override
 public List<ResolveInfo> queryIntentActivities(Intent intent,
                         int flags) {
   return queryIntentActivitiesAsUser(intent, flags, mContext.getUserId());
 }
  
 /** @hide Same as above but for a specific user */
 @Override
 public List<ResolveInfo> queryIntentActivitiesAsUser(Intent intent,
                         int flags, int userId) {
   try {
     return mPM.queryIntentActivities(
       intent,
       intent.resolveTypeIfNeeded(mContext.getContentResolver()),
       flags,
       userId);
   } catch (RemoteException e) {
     throw new RuntimeException("Package manager has died", e);
   }
 }

    可以看到,queryIntentActivities的真正实现是在PackageManagerService.java中,函数代码如下:

    

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public List<ResolveInfo> queryIntentActivities(Intent intent, String resolvedType, int flags, int userId) {
    if (!sUserManager.exists(userId))
      return Collections.emptyList();
    enforceCrossUserPermission(Binder.getCallingUid(), userId, false, "query intent activities");
    ComponentName comp = intent.getComponent();
    if (comp == null) {
      if (intent.getSelector() != null) {
        intent = intent.getSelector();
        comp = intent.getComponent();
      }
    }
   
    if (comp != null) {
      // Explicit的Intent,直接根据component得到对应的ActivityInfo
      final List<ResolveInfo> list = new ArrayList<ResolveInfo>(1);
      final ActivityInfo ai = getActivityInfo(comp, flags, userId);
      if (ai != null) {
        final ResolveInfo ri = new ResolveInfo();
        ri.activityInfo = ai;
        list.add(ri);
      }
      return list;
    }
   
    // reader
    synchronized (mPackages) {
      final String pkgName = intent.getPackage();
      if (pkgName == null) {
        // Implicit Intent
        return mActivities.queryIntent(intent, resolvedType, flags, userId);
      }
      final PackageParser.Package pkg = mPackages.get(pkgName);
      if (pkg != null) {
        // 指定了包名的Intent
        return mActivities.queryIntentForPackage(intent, resolvedType, flags, pkg.activities, userId);
      }
      return new ArrayList<ResolveInfo>();
    }
  }

    可以看到,Explicit Intent的实现较为简单,我们重点来看一下Implict Intent实现。Implicit Intent调用了queryIntent方法,我们来看一下queryIntent的实现代码:

  

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public List<ResolveInfo> queryIntent(Intent intent, String resolvedType, int flags, int userId) {
   if (!sUserManager.exists(userId))
     return null;
   mFlags = flags;
   return super.queryIntent(intent, resolvedType, (flags & PackageManager.MATCH_DEFAULT_ONLY) != 0, userId);
 }

    继续跟踪到IntentResolver.java的queryIntent方法,源码如下:

    

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public List<R> queryIntent(Intent intent, String resolvedType, boolean defaultOnly,
      int userId) {
    String scheme = intent.getScheme();
   
    ArrayList<R> finalList = new ArrayList<R>();
   
    // 最多有4轮匹配操作
    F[] firstTypeCut = null;
    F[] secondTypeCut = null;
    F[] thirdTypeCut = null;
    F[] schemeCut = null;
   
    // If the intent includes a MIME type, then we want to collect all of
    // the filters that match that MIME type.
    if (resolvedType != null) {
      int slashpos = resolvedType.indexOf('/');
      if (slashpos > 0) {
        final String baseType = resolvedType.substring(0, slashpos);
        if (!baseType.equals("*")) {
          if (resolvedType.length() != slashpos+2
              || resolvedType.charAt(slashpos+1) != '*') {
            // Not a wild card, so we can just look for all filters that
            // completely match or wildcards whose base type matches.
            firstTypeCut = mTypeToFilter.get(resolvedType);
            secondTypeCut = mWildTypeToFilter.get(baseType);
          } else {
            // We can match anything with our base type.
            firstTypeCut = mBaseTypeToFilter.get(baseType);
            secondTypeCut = mWildTypeToFilter.get(baseType);
          }
          // Any */* types always apply, but we only need to do this
          // if the intent type was not already */*.
          thirdTypeCut = mWildTypeToFilter.get("*");
        } else if (intent.getAction() != null) {
          // The intent specified any type ({@literal *}/*). This
          // can be a whole heck of a lot of things, so as a first
          // cut let's use the action instead.
          firstTypeCut = mTypedActionToFilter.get(intent.getAction());
        }
      }
    }
   
    // If the intent includes a data URI, then we want to collect all of
    // the filters that match its scheme (we will further refine matches
    // on the authority and path by directly matching each resulting filter).
    if (scheme != null) {
      schemeCut = mSchemeToFilter.get(scheme);
    }
   
    // If the intent does not specify any data -- either a MIME type or
    // a URI -- then we will only be looking for matches against empty
    // data.
    if (resolvedType == null && scheme == null && intent.getAction() != null) {
      firstTypeCut = mActionToFilter.get(intent.getAction());
    }
   
    FastImmutableArraySet<String> categories = getFastIntentCategories(intent);
    if (firstTypeCut != null) {
      buildResolveList(intent, categories, debug, defaultOnly,
          resolvedType, scheme, firstTypeCut, finalList, userId);
    }
    if (secondTypeCut != null) {
      buildResolveList(intent, categories, debug, defaultOnly,
          resolvedType, scheme, secondTypeCut, finalList, userId);
    }
    if (thirdTypeCut != null) {
      buildResolveList(intent, categories, debug, defaultOnly,
          resolvedType, scheme, thirdTypeCut, finalList, userId);
    }
    if (schemeCut != null) {
      buildResolveList(intent, categories, debug, defaultOnly,
          resolvedType, scheme, schemeCut, finalList, userId);
    }
    sortResults(finalList);
   
    return finalList;
  }

    具体的查询匹配过程是由buildResolveList函数完成了。查询的匹配实现我就不贴代码了,大家自己去查询看就好了。