CODEWITHSUNDEEP
androidandroid-context
Luis A. Florit
Luis A. Florit

Reputation: 2599

Please help me to understand Context

I have hard a big time trying to understand how Context stuff really works. I don't really need this now, but I am sure I will need this soon...

EXAMPLE

I made an app called ave and a library (itself an app) called xvf with several activities each. Most of them give info through a Toast, so I have everywhere the same method:

public void info(String txt) {
    Toast.makeText(getApplicationContext(), txt, Toast.LENGTH_LONG).show();
}

Now I thought to put that method as a class in the library, and call it from everywhere, both from the app classes and the library classes. I do not want to pass the context, like info.show(context, String), I want the class info to infer where the context is when it is being called.

So I made a class called info:

package com.floritfoto.apps.xvf;

import android.app.Activity;
import android.content.Context;
import android.widget.Toast;

public class info extends Activity{
    private Context context;

    public info() {
        super();
        context = (Context)getApplicationContext();
    }
    public void show(String txt) {
        Toast.makeText(context, txt, Toast.LENGTH_LONG).show();
    }
}

Then, on the calling activity, I just create an instance of info, and do info.show(String). This works.

Problem is that it seems too expensive for mee to extend Activity just to get the context...

Which is the correct way of doing what I want? It would be even better to do a info(String) thing... Remember, you are not allowed to make a constructor info(Context, String), that's cheating.

Upvotes: 0

Views: 173

Answers (1)

dmon
dmon

Reputation: 30168

I guess it's working by sheer blind luck.

You can't instantiate a proper Activity with new, you have to let the Android framework do that. In this case it's working because you're getting the Application context, which I guess it figures out by package owner.

In reality, an Activity is itself a Context (it extends it) so you could use this when showing a Toast. If you tried to do that in your info class I imagine it would fail. Anyway, like Eric pointed out, if you need a Context in a library class (that's not a proper Activity), you need to pass it in as a parameter to use it.

Upvotes: 2

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