java - 显式和隐式 Intent

Question

我对Intents 有点困惑。

为什么是

Intent implicit=new Intent(IDownload.class.getName());  

隐式 Intent

同时

Intent explicit=new Intent(implicit);  

是一个明确的 Intent ，但它似乎没有在其定义中添加任何新内容。系统似乎没有提取任何先前未由上面的 implicit Intent 提供的新信息？

在Android documentation (Intent types) ,

Explicit intents specify the component to start by name (the fully-qualified class name). You'll typically use an explicit intent to start a component in your own app, because you know the class name of the activity or service you want to start......

Intent implicit=new Intent(IDownload.class.getName()); 似乎满足了这个要求，但仍被视为隐式 Intent ，根据文档:

Implicit intents do not name a specific component, but instead declare a general action to perform, which allows a component from another app to handle it.....

Intent explicit=new Intent(implicit); 似乎与此矛盾，但仍被视为 Explicit intent。

更新 - 实现示例

引用:Binding to a Service

@Override
public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);

  setRetainInstance(true);

  appContext=(Application)getActivity().getApplicationContext();

  Intent implicit=new Intent(IDownload.class.getName());
  List<ResolveInfo> matches=getActivity().getPackageManager()
  .queryIntentServices(implicit, 0);

  if (matches.size() == 0) {
    Toast.makeText(getActivity(), "Cannot find a matching service!",
      Toast.LENGTH_LONG).show();
  }
  else if (matches.size() > 1) {
    Toast.makeText(getActivity(), "Found multiple matching services!",
      Toast.LENGTH_LONG).show();
  }
  else {
    ServiceInfo svcInfo=matches.get(0).serviceInfo;

    try {
      String otherHash=SignatureUtils.getSignatureHash(getActivity(),
        svcInfo.applicationInfo.packageName);
      String expected=getActivity().getString(R.string.expected_sig_hash);

      if (expected.equals(otherHash)) {
        Intent explicit=new Intent(implicit);
        ComponentName cn=new ComponentName(svcInfo.applicationInfo.packageName,
          svcInfo.name);

        explicit.setComponent(cn);
        appContext.bindService(explicit, this, Context.BIND_AUTO_CREATE);
      }
      else {
        Toast.makeText(getActivity(), "Unexpected signature found!",
          Toast.LENGTH_LONG).show();
      }
    }
    catch (Exception e) {
      Log.e(getClass().getSimpleName(), "Exception trying to get signature hash", e);
    }
  }
}

Answer 1

链接示例包括这些行

      Intent explicit=new Intent(implicit);
      ComponentName cn=new ComponentName(svcInfo.applicationInfo.packageName,
        svcInfo.name);

      explicit.setComponent(cn);

第一行只是创建一个新的 Intent 实例，它是旧实例的副本。虽然变量可能是显式，但此时它仍然是隐式 Intent 。

第二行根据先前 getActivity().getPackageManager().queryIntentServices(implicit, 0) 调用的单个匹配结果创建一个 ComponentName 对象。在这一点上，explicit 仍然是隐式 Intent 。

第三行是魔法。一旦将特定的 ComponentName 分配给 Intent 实例，explicit 就真正成为了显式 Intent 。