Develop Reference

MediaManager volume control for Xamarin.Forms

I'm trying to make a radio app with MediaManager on Xamarin.Forms for Android and iOS. I want to include a volume slider in the app. I've implemented it like this in XAML:
<Slider x:Name="slider" Grid.Column="1" Grid.ColumnSpan="3" Grid.Row="4" VerticalOptions="Center" ValueChanged="ChangeMediaVolume" Minimum="0" Maximum="10" Value="5" Margin="5"/>
And for the code behind I've used this method:
private void ChangeMediaVolume(object sender, ValueChangedEventArgs args)
{
int value = (int)slider.Value;
CrossMediaManager.Current.Volume.MaxVolume = 10;
CrossMediaManager.Current.Volume.CurrentVolume = value;
}
It works perfectly in the iOS emulator, but when I launch my Android emulator, it crashes and highlights the CrossMediaManager items with the message
System.NullReferenceException has been thrown. Object reference not
set to an instance of an object.
I'm not quite sure how to fix it or why it works for one platform and not the other.

Yes. This is a plugin issue, I got the same result, here is a workaround for android.
You can use dependenceService to achieve that.
1.Create a interface.
public interface IControlVolume
{
int setControlVolume(int value);
}
2.Achieve it in android.
[assembly: Dependency(typeof(MyControlVolume))]
namespace VideoPlay.Droid
{
class MyControlVolume : IControlVolume
{
public int setControlVolume(int value)
{
var audioMgr = (AudioManager)Forms.Context.GetSystemService(Context.AudioService);
//set the volume
audioMgr.SetStreamVolume(Android.Media.Stream.Music, value,VolumeNotificationFlags.PlaySound);
//get current value
int Volume = audioMgr.GetStreamVolume(Android.Media.Stream.Music);
return Volume;
}
}
}
Here is running gif.
https://imgur.com/a/odE79sc

So I seem to have figured out the issue. When I launch the app, the player doesn’t start until the play button has been pressed. Because of this, when the app launches the crossmediamanager isn’t fully instantiated. This is why it’s returning a null. I caught the exception so that it would load, and once the player starts everything works perfectly.

QR code reader to extract data

i have a sales summary print out and has a QR Code ,
i want to develop an app (IOS and android) that reads the QR code , extract all information,do some calculations,and display in specific form , i tried zxing library but it did not extract all information from the receipt.any tip?

You can use google vision API to achieve this. I personally used this and found it great. The below code snippets should help you.
Put this below line in the gradle.
compile 'com.google.android.gms:play-services:9.4.0'
Use BarcodeDetector and CameraSource classes to capture the QR code on real time and decode it.
barcodeDetector.setProcessor(new Detector.Processor<Barcode>() {
#Override
public void release() {
}
#Override
public void receiveDetections(Detector.Detections<Barcode> detections) {
final SparseArray<Barcode> barcodes = detections.getDetectedItems();
if (barcodes.size() != 0) {
barcodeInfo.post(new Runnable() { // Use the post method of the TextView
public void run() {
barcodeInfo.setText( // Update the TextView
barcodes.valueAt(0).displayValue
);
}
});
}
}
});
Use a SparseArray to fetch the detections and the displayValue of the elements of this sparse array returns the deocded string.
After extracting the string one can do anything, be it displaying the string or make some calculation out of it etc.

This library is the most popular and easiest of reading QR codes in your Android application.
You should also have a look at the Wiki section of this library for learning about how to integrate this library into your Android Application and how to use this library.
This is how you can use this library.
1. Add this library to your project by adding following line into your dependencies inside build.gradle(Module: app) file
compile 'com.github.nisrulz:qreader:2.0.0'
2. Then, after syncing project files, add the SurfaceView element provided by this library into your XML layout file.
<SurfaceView
android:id="#+id/camera_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>
3. Declare the SurfaceView & QREader inside your Activity's Java file & then initialize it inside onCreate() method.
class MainActivity extends AppCompatActivity{
private SurfaceView mySurfaceView;
private QREader qrEader;
#Override
protected void onCreate(final Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Setup SurfaceView
// -----------------
mySurfaceView = (SurfaceView) findViewById(R.id.camera_view);
// Init QREader
// ------------
qrEader = new QREader.Builder(this, mySurfaceView, new QRDataListener() {
#Override
public void onDetected(final String data) {
Log.d("QREader", "Value : " + data);
text.post(new Runnable() {
#Override
public void run() {
text.setText(data);
}
});
}
}).facing(QREader.BACK_CAM)
.enableAutofocus(true)
.height(mySurfaceView.getHeight())
.width(mySurfaceView.getWidth())
.build();
}
4. Initialize it inside onResume()
#Override
protected void onResume() {
super.onResume();
// Init and Start with SurfaceView
// -------------------------------
qrEader.initAndStart(mySurfaceView);
}
There are many more possibilities you can do with this library, so I recommend you to visit the GitHub repository and check it out. It's worth a shot!

How to change Vuforia AR camera focus mode?

I am using Vuforia 6.2 AR SDK for in Unity. But while I test the application in Android phone the camera seems like blurry. I searched in Vuforia's developer website and found some camera focus mode but I can't implement because that guideline was for older Vuforia SDK, I can't find the script they mentioned in their website. Here is their code sample but it's not working. I created different script and run this line on Start() function, but still not working.
CameraDevice.Instance.SetFocusMode(
CameraDevice.FocusMode.FOCUS_MODE_CONTINUOUSAUTO);

try this
void Start ()
{
VuforiaARController.Instance.RegisterVuforiaStartedCallback(OnVuforiaStarted);
VuforiaARController.Instance.RegisterOnPauseCallback(OnPaused);
}
private void OnVuforiaStarted()
{
CameraDevice.Instance.SetFocusMode(
CameraDevice.FocusMode.FOCUS_MODE_CONTINUOUSAUTO);
}
private void OnPaused(bool paused)
{
if (!paused) // resumed
{
// Set again autofocus mode when app is resumed
CameraDevice.Instance.SetFocusMode(
CameraDevice.FocusMode.FOCUS_MODE_CONTINUOUSAUTO);
}
}

This code is the right code.
bool cameramode = false;
public void OnCameraChangeMode()
{
Vuforia.CameraDevice.CameraDirection currentDir = Vuforia.CameraDevice.Instance.GetCameraDirection();
if (!cameramode) {
RestartCamera(Vuforia.CameraDevice.CameraDirection.CAMERA_FRONT);
camBtnTxt.text = "Back Camera";
} else {
RestartCamera(Vuforia.CameraDevice.CameraDirection.CAMERA_BACK);
camBtnTxt.text = "Front Camera";
}
}
private void RestartCamera(Vuforia.CameraDevice.CameraDirection newDir)
{
Vuforia.CameraDevice.Instance.Stop();
Vuforia.CameraDevice.Instance.Deinit();
Vuforia.CameraDevice.Instance.Init(newDir);
Vuforia.CameraDevice.Instance.Start();
}

NativeScript : custom camera view

I am working on an iOS and Android application with a custom camera view (that's why I won't use camera module http://docs.nativescript.org/ApiReference/camera/README)
I need to have my own UI above the camera preview.
Can I do this with Nativescript ?
I could not find any module/plugin with this feature.
Is this hard to write my own module?

The Placeholder allows you to add any native widget to your application. To do that, you need to put a Placeholder somewhere in the UI hierarchy and then create and configure the native widget that you want to appear there. Finally, pass your native widget to the event arguments of the creatingView event.
NativeScript does not have a surface view and you need to use placeholder on top of camera plugin.
<Placeholder (creatingView)="creatingView($event)"></Placeholder>
public creatingView(args: any) {
var nativeView = new android.view.SurfaceView(application.android.currentContext);
args.view = nativeView;
}

Use the surfaceview in layout.xml
<SurfaceView
android:id="#+id/surfaceview"
android:layout_centerHorizontal="true"
android:layout_width="350dp"
android:layout_height="260dp" />
use following code in activity class
SurfaceView surfaceView;
CameraSource cameraSource;
final TextRecognizer textRecognizer = new TextRecognizer.Builder(getApplicationContext()).build();
cameraSource = new CameraSource.Builder(getApplicationContext(), textRecognizer)
.setFacing(CameraSource.CAMERA_FACING_BACK)
.setAutoFocusEnabled(true)
.build();
surfaceView.getHolder().addCallback(new SurfaceHolder.Callback() {
#Override
public void surfaceCreated(SurfaceHolder surfaceHolder) {
try {
cameraSource.start(surfaceView.getHolder());
} catch (IOException e) {
e.printStackTrace();
}
}
#Override
public void surfaceChanged(SurfaceHolder surfaceHolder, int i, int i1, int i2) {
}
#Override
public void surfaceDestroyed(SurfaceHolder surfaceHolder) {
cameraSource.stop();
}
});
textRecognizer.setProcessor(new Detector.Processor<TextBlock>() {
#Override
public void release() {
}

I don't understand exactly your scenario, but what I have in one of my apps that has a barcode scanner (that uses a custom camera view as in your question?) which I wanted to have a laser beam line in the middle of the camera view-port, is this:
<GridLayout>
<YourCameraView />
<StackLayout id="laser"></StackLayout>
</GridLayout>
This enables you to have the laser on top of the YourCameraView element and you can position the laser element using vertical-align and horizontal-align CSS properties.
If you want more freedom, substitute the GridLayout with AbsoluteLayout, so then you can position the overlay elements (i.e. the laser element) using top and left CSS properties.

Revmob fullscreen ad preload on Unity?

Is there any way to preload fullscreen ad on Unity? Right now when we call it using
revmob.ShowFullscreen();
when we create end game screen. But most of the time it loads after 5/10 secs later which is in-game most probably if you press restart, so it shows a full screen ad during gameplay.
I've found some ways to preload it on native android and tried same function to see if they exists in Unity but no luck.
Thanks.

Yes! You can use the following code:
private RevMobFullscreen fullscreen;
fullscreen = revmob.CreateFullscreen();
fullscreen.show();
If you need more information, you can access RevMob mobile ad network website: https://www.revmobmobileadnetwork.com

It will be better to add this code to the Create statement:
private RevMobFullscreen fullscreen;
fullscreen = revmob.CreateFullscreen();
...and then also this code to the listener:
RevMobAdsListener revmobListener = new RevMobAdsListener() {
// Required
#Override
public void onRevMobSessionIsStarted() {
fullscreen.show();
}
(...)
}
This will show the fullscreen ad.

You can do like this to preload revmob videos in unity. But there are memory leaks in revmob unity videos and they might fix that in 9.2.x...
REVMOB_APP_IDS = new Dictionary<string, string>() {
{ "Android", androidMediaId},
{ "IOS", iosMediaId }
};
revmob = RevMob.Start (REVMOB_APP_IDS, gameObject.name);
public void SessionIsStarted ()
{
CacheVideoInterstitial("Bootup");
}
public void CacheVideoInterstitial(string location) {
DestroyVideo();
StartCoroutine(CacheAfterEndofFrame(location));
}
IEnumerator CacheAfterEndofFrame(string location) {
yield return null;
fullscreenVideo = revmob.CreateVideo(location);
}
void DestroyVideo() {
if( fullscreenVideo != null ) {
fullscreenVideo.Hide();
//fullscreenVideo.Release();
//fullscreenVideo = null;
}
}
// revmob ad closing delegate
public void UserClosedTheAd (string revMobAdType)
{
DestroyVideo();
CacheVideoInterstitial(this.location);
}