Android -如何将字符串从Alertdialog发送到片段

public class MyFragment extends Fragment {
    // ...

    public void receiveStringFromDialog(String str) {
        // 处理接收到的字符串
        // ...
    }

    // ...
}

public class MainActivity extends AppCompatActivity {
    // ...

    private void showDialog() {
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle("输入字符串");
        final EditText editText = new EditText(this);
        builder.setView(editText);
        builder.setPositiveButton("发送", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                String str = editText.getText().toString();
                MyFragment fragment = (MyFragment) getSupportFragmentManager().findFragmentById(R.id.fragment_container);
                fragment.receiveStringFromDialog(str);
            }
        });
        builder.show();
    }

    // ...
}