blocks|key|1155895|text|从Service类内部：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1155896|Intent+dialogIntent+=+new+Intent(this,+MyActivity.class);
dialogIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(dialogIntent);|code-block|syntax|javascript|1155897|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

From inside the Service class:

<pre><code>Intent dialogIntent = new Intent(this, MyActivity.class);
dialogIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(dialogIntent);
</code></pre>

blocks|key|1155935|text|值得一提的是:当我们的任务在后台时，上面的答案可以很好地工作，如果我们的任务(由服务%2B一些活动组成)在前台(即用户可以看到我们的活动之一)，我可以让它工作的唯一方法是这样的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1155936|++++Intent+intent+=+new+Intent(storedActivity,+MyActivity.class);
++++intent.setAction(Intent.ACTION_VIEW);
++++intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
++++intent.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
++++storedActivity.startActivity(intent);|code-block|syntax|javascript|1155937|我不知道ACTION_VIEW或FLAG_ACTIVITY_NEW_TASK在这里有什么实际的用处。成功的关键是|1155938|storedActivity.startActivity(intent);|1155939|当然还有FLAG_ACTIVITY_REORDER_TO_FRONT，因为它不会再次实例化该活动。祝你好运！|1155940|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Another thing worth mentioning: while the answer above works just fine when our task is in the background, the only way I could make it work if our task (made of service + some activities) was in the foreground (i.e. one of our activities visible to user) was like this:

<pre><code> Intent intent = new Intent(storedActivity, MyActivity.class);
 intent.setAction(Intent.ACTION_VIEW);
 intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
 intent.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
 storedActivity.startActivity(intent);
</code></pre>

I do not know whether ACTION_VIEW or FLAG_ACTIVITY_NEW_TASK are of any actual use here. The key to succeeding was

<pre><code>storedActivity.startActivity(intent);
</code></pre>

and of course FLAG_ACTIVITY_REORDER_TO_FRONT for not instantiating the activity again. Best of luck!

blocks|key|1155985|text|我也有同样的问题，我想让你知道上面的方法都不适用于我。对我起作用的是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1155986|+Intent+dialogIntent+=+new+Intent(this,+myActivity.class);
+dialogIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
+this.startActivity(dialogIntent);|code-block|syntax|javascript|1155987|在我的一个子类中，存储在一个单独的文件中，我必须：|1155988|public+static+Service+myService;

myService+=+this;

new+SubService(myService);

Intent+dialogIntent+=+new+Intent(myService,+myActivity.class);
dialogIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
myService.startActivity(dialogIntent);|1155989|所有其他答案都给了我一个nullpointerexception。|offset|length|style|CODE|1155990|entityMap^0|0|0|0|0|C|K|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@$M|X|N|Y|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

I had the same problem, and want to let you know that none of the above worked for me.
What worked for me was:

<pre><code> Intent dialogIntent = new Intent(this, myActivity.class);
 dialogIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
 this.startActivity(dialogIntent);
</code></pre>

and in one my subclasses, stored in a separate file I had to: 

<pre><code>public static Service myService;

myService = this;

new SubService(myService);

Intent dialogIntent = new Intent(myService, myActivity.class);
dialogIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
myService.startActivity(dialogIntent);
</code></pre>

All the other answers gave me a <code>nullpointerexception</code>.

blocks|key|941845|text|如果你需要从你的服务中重新调用一个活动，我建议使用下面的链接。Intent.FLAG_ACTIVITY_NEW_TASK不是解决方案。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|941846|https://stackoverflow.com/a/8759867/1127429|offset|length|941847|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|17|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@$D|O|E|P|1|Q]]|A|$]]|$1|F|3|-4|5|6|7|R|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|C]]]]

If you need to recal an Activity that is in bacgrounde, from your service, I suggest the following link. Intent.FLAG_ACTIVITY_NEW_TASK is not the solution.

<a href="https://stackoverflow.com/a/8759867/1127429">https://stackoverflow.com/a/8759867/1127429</a>

blocks|key|1156041|text|或者，|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1156042|您可以使用自己的Application类并从需要的任何地方调用(特别是非活动)。|1156043|public+class+App+extends+Application+{

++++protected+static+Context+context+=+null;

++++@Override
++++public+void+onCreate()+{
++++++++super.onCreate();
++++++++context+=+getApplicationContext();
++++}

++++public+static+Context+getContext()+{
++++++++return+context;
++++}

}|code-block|syntax|javascript|1156044|并注册您的Application类：|1156045|<application+android:name="yourpackage.App"+...|1156046|然后调用：|1156047|App.getContext();|1156048|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

Alternately,

You can use your own Application class and call from wherever you needs (especially non-activities).

<pre><code>public class App extends Application {

 protected static Context context = null;

 @Override
 public void onCreate() {
 super.onCreate();
 context = getApplicationContext();
 }

 public static Context getContext() {
 return context;
 }

}
</code></pre>

And register your Application class :

<pre><code>&lt;application android:name="yourpackage.App" ...
</code></pre>

Then call :

<pre><code>App.getContext();
</code></pre>

blocks|key|1156091|text|不能使用Service的Context；可以像这样获得(包)+Context：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1156092|Intent+intent+=+new+Intent(getApplicationContext(),+SomeActivity.class);|code-block|syntax|javascript|1156093|entityMap^0|4|7|C|7|V|7|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|U|8|@]|D|@]|E|$]]]|L|$]]

one cannot use the <code>Context</code> of the <code>Service</code>; was able to get the (package) <code>Context</code> alike:

<pre><code>Intent intent = new Intent(getApplicationContext(), SomeActivity.class);
</code></pre>

Android:
<pre><code>public class LocationService extends Service {

 @Override
 public void onStart(Intent intent, int startId) {
 super.onStart(intent, startId);
 startActivity(new Intent(this, activity.class));
 }
}
</code></pre>
I launched this service from <code>Activity</code>
In <code>Activity</code> if condition satisfies start
<pre><code>startService(new Intent(WozzonActivity.this, LocationService.class));
</code></pre>
from my <code>LocationService</code> mentioned above could not launch <code>Activity</code>, how can I get context of current running <code>Activity</code> in service class?

Start Activity from Service in Android

Android

Android：public class LocationService extends Service {    @Override    public void onStart(Intent intent, int startId) {        super.onStart(intent, startId); ...

问在Android中从Service启动Activity
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