Use startActivityForResult from non-activity

Question

I have MainActivity which is an Activity and other class(which is a simple java class), we'll call it "SimpleClass".

Now I want to run from that class the command startActivityForResult.

I though that I could pass that class (SimpleClass), using only MainActivity's context, but the problem is that we can't run context.startActivityForResult(...);.

So, the only way making SimpleClass to use startActivityForResult, is to pass the reference of MainActivity as an Activity variable to the SimpleClass.

Something like that:

Inside the MainActivity class I created the instance of SimpleClass like this way:

SimpleClass simpleClass = new SimpleClass(MainActivity.this);

Now, this is how SimpleClass looks like:

public Class SimpleClass {

Activity myMainActivity;

   public SimpleClass(Activity mainActivity) {
       super();
       this.myMainActivity=mainActivity;    
   }
....


    public void someMethod(...) {
        myMainActivity.startActivityForResult(...);
    }

}

Now it's working, but isn't there a proper way of doing this? I am afraid I could have some memory leaks in the future.

I don't know what you are trying to do but you should read [this](http://stackoverflow.com/questions/2253088/passing-activity-to-non-activity-object-properly). — Macarse, May 17 '10 at 12:06
By doing this could you use the `onActivityResult` method inside your simpleClass or you did not intend to? [Same problem here..](http://stackoverflow.com/questions/25557087/how-to-get-the-result-from-onactivityresult-inside-another-classoutside-of-the/25557182?noredirect=1#comment39915501_25557182) — Vivere_FlowCoder, Aug 29 '14 at 08:27

score 68 · Answer 1 · edited Sep 14 '16 at 02:20

68

I don't know if this is good practice or not, but casting a Context object to an Activity object compiles fine.

Try this:

if (mContext instanceof Activity) {
        ((Activity) mContext).startActivityForResult(...);
} else {
        Log.e("mContext should be an instanceof Activity.");
}

This should compile, and the results should be delivered to the actual activity holding the context.

edited Sep 14 '16 at 02:20

Sakiboy

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answered Dec 29 '11 at 08:53

Some Noob Student

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How about if context is passed from a service ? – Madhur Ahuja Oct 23 '13 at 08:24
9

No, it does launch a cast exception! – Lisa Anne Dec 12 '13 at 16:48
2

A Context is not inevitably an Activity (for example if it's get with `myActivity.getApplicationContext()` – Hugo Gresse Jan 29 '15 at 10:15
If the goal is to avoid a memory leak, what advantage is there to holding a context as a member variable of a class over holding an activity? Doesn't storing a context have the same potential to lead to a memory leak as storing an activity? – stevehs17 Feb 07 '16 at 22:32

score 4 · Answer 2 · answered May 28 '10 at 19:36

4

If you need to get the result from the previous Activity, then your calling class needs to be of type Activity.

What is the purpose of you calling Activity.startActivityForResult() if you never use the result (at least according to the sample code you posted).

Does myMainActivity do anything with the result? If so, then just make SimpleClass a subclass of Activity and handle the result from within SimpleClass itself.
If myMainActivity needs the result, then maybe you should refactor the code to start the activity from myMainActivity.

answered May 28 '10 at 19:36

codinguser

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I am using result, just i wanna seperate it to diffrent class, so i was wondering how should i pass an Activity parameter to a non-activity class, without causing leaks in the future. – rayman May 30 '10 at 11:06
1

What about making SimpleClass a nested class? – codinguser May 30 '10 at 20:38

score 1 · Answer 3 · answered Oct 13 '11 at 11:27

1

Better solution is :

Making SimpleClass a subclass of your Activity class
calling another Activity as startActivityForResult
handling the result within SimpleClass itself

answered Oct 13 '11 at 11:27

gtiwari333

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sounds like this should work, but I got this: `java.lang.NullPointerException: Attempt to invoke virtual method 'android.app.ActivityThread$ApplicationThread android.app.ActivityThread.getApplicationThread()' on a null object reference` – Boy Jan 28 '16 at 09:22

Use startActivityForResult from non-activity

3 Answers3

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