Define MainActivity as static variable in order to access findViewById method

Question

While I was coding, I wanted to use findViewById method to find a view that cant access in the current view but can be accessed via the MainActivity. So two options came to my mind. One is creating a static method from that object in the MainActivity class and access the static object. The second method is to create a static object form MainActivity class itself(this) and access the findViewById method by calling the static object. Please answer the method I should use. And apart from that, it got me thinking that whether an Android developer should come across this type of scenario or whether I have done some improper coding to access findViewById method in MainActivity while I was in a different view. You can take a look at the code in the below repo.

https://github.com/chrish2015/ExpenseTrackerLatest

Thanks

Answer 1

If you are inside a class that is neither a Context nor an Activity and you need to use a method which exists inside the activity or context, then simply pass the activity as a parameter to that class and take an instance to that activity inside your class.

public class MyAdapter extends ArrayAdapter { // this is not activity
    private Activity mActivity; // activity is a member of this class.

    public MyAdapter(Activity activity, List<String> data) {
        mActivity = activity;
    }

    public View getView(...) {
        // if you need to use findViewById: 
        View view = mActivity.findViewById(R.id.some_id);
    }

}

Answer 2

Don't use any of your two methods.

I might be misunderstanding your first sentence, but just to be sure, are you asking for a way to access a View that exists in the MainActivity, while you're inside of a Fragment?

If that's what you're asking, then yes, as an Android Developer, there will definitely be moments where we come across this scenario. However, the solution is definitely NOT by making your Views or Context static.

This is one of the easiest ways to cause bugs to appear throughout your app, with a very high chance to cause memory leaks too. Here's an Article from Google talking about memory leaks related to keeping a reference to a Context: https://android-developers.googleblog.com/2009/01/avoiding-memory-leaks.html

Rather than your two options, there are better solutions that developers typically use.

First of all, keep in mind that you should NOT be directly accessing any Views from outside of your current layout... meaning, that if you're in a second Activity, you don't directly access Views from the first Activity, or if you're in a Fragment, you don't directly access Views that belong to it's FragmentActivity.

Instead, you let the Activity or Fragment handle it's own Views.

So for example, if you're in another Activity and you want to update some data in the previous Activity, you can take advantage of an Activity's startActivityForResult() and onActivityResult() to obtain the data necessary to update the Activity immediately upon returning to the app.

For Fragments, there's actually a tutorial from the Android Documentation that describes a very good way to communicate between other Fragments: https://developer.android.com/training/basics/fragments/communicating

This method is to use interfaces as a callbacks, so another Fragment or the Activity will be able to receive data and update it's Views within it's own layout.

So for your case, if you're using Fragments and an Activity, you can easily have your fragments and activities communicate to each other in a safer and more reliable way.

Also, make sure you read up more on static and it's effects on your code, especially the side effects on Android components. Do not carelessly use static without considering some of the effects it might cause, because that would cause an endless amount of trouble to your code.