We know that Alert dialog boxes are used to show some popup to user so that user can perform some action. But with Activity dialog you can manage the visibility of dialog based on activity life cycles.

To create an activity as a dilaog we have to set theme for that activity in manifest file like this :

<activity android:theme="@android:style/Theme.Dialog" />

// and in your Activity you can show your activity dialog as :

public class BaseActivity extends Activity {

    Button btnClick;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        btnClick = (Button) findViewById(R.id.btnClick);
        btnClick.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                Intent intent = new Intent(BaseActivity.this, ActivityDialog.class);
                startActivity(intent);
            }
        });
    }

}

and your Activity Dialog class is :

public class ActivityDialog extends Activity implements OnClickListener {

    Button btnCancel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_dialog);


        btnCancel_btn = (Button) findViewById(R.id.cancel_btn_id);

       btnCancel.setOnClickListener(this);
    }

   @Override
    public void onClick(View v) {

        switch (v.getId()) {
        case R.id.cancel_btn_id:

        Toast.makeText(getApplicationContext(), message, Toast.LENGTH_SHORT)
                .show();
            this.finish();
            break;
        }
    }