Develop Reference

Making phone call in windows phone 8.1 in a single tap

I'm writing an emergency app and so I need to allow the user to make phone call in a single tap. All the articles I've been reading so far allows phone call in 2 taps. Is there a way to do that in only one tap?

How to invoke system camera from custom Windows phone 8.1.app

Is there a way to use default camera app(Nokia/Microsoft camera) in my app?
I would like to, on btn click to call system camera. Take a picture with it, and then upload that picture to the server from my app.
If there is no way to do that, what is the best way to create camera app so user can use zoom, flashlight, etc.
EDIT:
This was available in older versions of Windows phone, and it was simple to use
like this:
CameraCaptureTask camera = new CameraCaptureTask();
camera.Show();
camera.Completed += new EventHandler<PhotoResult>(camera_Completed);
I don't understand why would MS remove this ability from Windows phone 8.1
Thank you,
regards

The camera capture task was based on Silverlight APIs and was valid for Windows phone 7 and 8 that used silverlight Pages . The camera APIs are now based on WinRT Universal APIs . Have a look at this
https://channel9.msdn.com/Series/Building-Apps-for-Windows-Phone-8-1/17

You can do by this link,
capturing an image in windows store 8.1

How can we detect system volume in WIndows 8?

If I have an app that plays sounds. It seems like a good idea to indicate why the user isn't hearing the sounds. Is there a way to detect system volume or MUTE?

Yes.
MediaControl.SoundLevel for Windows 8
SystemMediaTransportControls.SoundLevel for Windows 8.1 and later
Music and media capture apps should monitor the SoundLevel to determine whether the audio streams on the app have been Muted.

I think you can use Windows.Media namespace. Also these is SoundLevel enum.
Also
ISimpleAudioVolume interface

Control speaker volumes with c#

is there any easy way to control the individual speaker volumes in Windows 7 with c#?
I just want to set the volumes to a "preset", because windows likes to reset them randomly...

Start here,
Use IAudioMeterInformation in the CoreAudio APIs in Vista and Win 7.
Managed wrappers are available in NAudio (get at the AudioMeterInformation from the MMDevice).
check this too Get Master Sound Volume in c#

How to programmatically determine system device sound settings?

I have to write a simple Silverlight app for WP7. If the phone is muted in system, the program must not play sounds, but if the phone is not muted the program must play sounds.
How to programmatically determine if Windows Phone is muted or not?

There is no need to do that, the system does not play any sounds when the phone is muted. The system setting overrides all other settings both in Silverlight and XNA (and in integrated Silverlight + XNA).