Q:

Runtime Permission at Startup

I have a flashlight that needs CAMERA and WRITE_SETTINGS permissions, I need to first handle these permissions which I already know how to do it, Then if it is granted, for example, start my main activity...
(sorry, I am new in android)

A:

Add this library from github in your gradle file
Than add this code
PermissionListener permissionlistener = new PermissionListener() {
    @Override
    public void onPermissionGranted() {
        //The user have conceded permission
        Toast.makeText(MainActivity.this, "Permission Granted", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onPermissionDenied(ArrayList<String> deniedPermissions) {
        //close the app or do whatever you want
        Toast.makeText(MainActivity.this, "Permission Denied\n" + deniedPermissions.toString(), Toast.LENGTH_SHORT).show();
    }
};

new TedPermission(this)
.setPermissionListener(permissionlistener)
.setDeniedMessage("If you reject permission,you can not use this service\n\nPlease turn on permissions at [Setting] > [Permission]")
.setPermissions(Manifest.permission.READ_CONTACTS, Manifest.permission.ACCESS_FINE_LOCATION)
.check();

Or if you prefer do it natively, check in the google docs

