Activityに依存しないようにFragment->Activityへ通知をする

InterfaceFragment.java

package com.esperia09.android.test_fragment;

import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;

public class InterfaceFragment extends Fragment {
    public static final String KEY_LEVEL = "level";

    public static InterfaceFragment newInstance(int level) {
        InterfaceFragment frg = new InterfaceFragment();
        Bundle args = new Bundle();
        args.putInt(KEY_LEVEL, level);
        frg.setArguments(args);
        return frg;
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        Button button = new Button(getActivity());
        button.setText(String.valueOf(getArguments().getInt(KEY_LEVEL)));
        button.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                if (getActivity() instanceof OnClickBtnListener) {
                    OnClickBtnListener l = (OnClickBtnListener) getActivity();
                    l.onClickBtn("hogehoge");
                }
            }
        });
        return button;
    }

    public interface OnClickBtnListener {
        public void onClickBtn(String msg);
    }
}

MainActivity.java

package com.esperia09.android.test_fragment;

import android.app.Activity;
import android.app.FragmentManager;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Toast;

public class MainActivity extends Activity implements InterfaceFragment.OnClickBtnListener {

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

        FragmentManager fm = getFragmentManager();
        InterfaceFragment frg = (InterfaceFragment) fm.findFragmentById(android.R.id.content);
        if (frg == null) {
            frg = InterfaceFragment.newInstance(0);
            fm.beginTransaction().add(android.R.id.content, frg).commit();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        menu.add("stack");
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        if ("stack".equals(item.getTitle())) {
            FragmentManager fm = getFragmentManager();
            InterfaceFragment nowFrg = (InterfaceFragment) fm
                    .findFragmentById(android.R.id.content);
            int level = nowFrg.getArguments().getInt(InterfaceFragment.KEY_LEVEL);
            fm.beginTransaction()
                    .replace(android.R.id.content, InterfaceFragment.newInstance(++level))
                    .addToBackStack(null).commit();

        }
        return true;
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
    }

    @Override
    public void onClickBtn(String msg) {
        Toast.makeText(getApplicationContext(), msg, Toast.LENGTH_SHORT).show();
    }
}

ありがたいサンプルを頂いたので貼っておきます！！

Interfaceは二段構えにした方がいいよサンプル
https://github.com/vvakame/AndroidUtil/blob/master/main/src/net/vvakame/android/fragment/BeamFragment.java
https://twitter.com/vvakame/status/240298983132655616

InterfaceでFragment返してしまうのありだよサンプル
https://github.com/eaglesakura/eglibrary/blob/work-rmfragment/eglibrary-google/src/com/eaglesakura/lib/net/google/drive/fragment/GoogleOAuth2Fragment.java
https://twitter.com/eaglesakura/status/240301912161923072