如何在android中以编程方式创建透明的activity？

<activity android:name=".TransparentActivity"
    android:theme="@android:style/Theme.Translucent.NoTitleBar" />

public class TransparentActivity extends Activity {
    // ...
}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_transparent);
    getWindow().setBackgroundDrawable(new ColorDrawable(android.graphics.Color.TRANSPARENT));
}

Intent intent = new Intent(MainActivity.this, TransparentActivity.class);
startActivity(intent);