zxing手电筒在UI上不显示

<uses-permission android:name="android.permission.CAMERA" />

boolean isFlashAvailable = getPackageManager().hasSystemFeature(PackageManager.FEATURE_CAMERA_FLASH);

<Button
    android:id="@+id/flashlight_button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Flashlight"
    android:onClick="toggleFlashlight" />

private CameraManager cameraManager;
private boolean isFlashlightOn = false;

public void toggleFlashlight(View view) {
    if (isFlashlightOn) {
        cameraManager.turnOffFlashlight();
        isFlashlightOn = false;
    } else {
        cameraManager.turnOnFlashlight();
        isFlashlightOn = true;
    }
}