Xamarin - Under the bridge

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Xamarin - Under the Bridge
Microsoft&Xamarin MVP, Xamarin Certified Mobile Developer
CTO Mahiz S.r.l.
dan.ardelean@mahiz.it Twitter: @danardelean
Dan Ardelean

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XAMARIN

XAMARIN
C#/F#
Visual Studio
Xamarin Studio
Black Magic
Native

iOS Native Applications

iOS Native Application

DEMO XCODE
SINGLE VIEW APPLICATION

C# to Objective-C world

Xamarin iOS Compilation

• Expose Objectve-C to C# using Selectors
• objc_msgSend functions
Selectors
-[NSString sizeWithFont:forWidth:lineBreakMode:]
sizeWithFont Selector:
- (CGSize)sizeWithFont:(UIFont *)font forWidth:(CGFloat)width lineBreakMode:(UILineBreakMode)lineBreakMode
Objective-C declaration:
CGSize objc_msgSend(IntPtr target, IntPtr selector, IntPtr font, nfloat width, UILineBreakMode mode);
objc_msgSend
[DllImport (Constants.ObjectiveCLibrary,EntryPoint="objc_msgSend")]
static extern CGSize cgsize_objc_msgSend_IntPtr_float_int ( IntPtr target, IntPtr selector, IntPtr font,
nfloat width, UILineBreakMode mode);

• Expose Objectve-C to C# using Selectors
• objc_msgSend functions
Selectors
NSString target = ...
Selector selector = new Selector ("sizeWithFont:forWidth:lineBreakMode:");
UIFont font = ...
nfloat width = ...
UILineBreakMode mode = ...
CGSize size = cgsize_objc_msgSend_IntPtr_float_int( target.Handle, selector.Handle, font == null ?
IntPtr.Zero : font.Handle, width, mode);

• Expose Managed Code to Objective-C
Registrars
[Register]
class MyViewController : UIViewController{
[Export ("myFunc")]
public void MyFunc () { }
}
C# (Managed Code)
Objective-C
@interface MyViewController : UIViewController { }
-(void)myFunc;
@end
@implementation
MyViewController {}
-(void) myFunc
{ /* code to call the managed MyViewController.MyFunc method */
}
@end

DEMO XAMARIN IOS
Single View Application

Xamarin.iOS creates a managed wrapper, called a peer
object, for every native object accessed by the
Xamarin.iOS runtime
Peer wrapper objects
UIKit.UIButton
(peer object)
[UIButton]
(native object)IntPtrHandle
Allocated by
Xamarin.iOS
and collected by the
GC
Allocated by the iOS
runtime
and reference counted

• Peer object increment the retain count; it is released
when the managed peer is disposed or finalized
Memory allocation Xamarin.iOS
1
GC
Collect
[brelease] 0
b =null;
b.Dispose(); [brelease] 0
var b = new UIButton(...) [[UIButton alloc]init]
…
or

Monitoring memory allocations
Memory
Analysis
(Heap shot)
Instrument
s
Androi
d
Device
Monitor
Xamarin
Profiler
VS
Profiler

DEMO MEMORY ALLOCATION
Single View Application

Prefer full delegate methods over lambdas – it makes it
easier to see and understand strong references
Call Dispose() to release native resources immediately (vs.
waiting ona GC) when you are finished with a peer
wrapper
Always unsubscribe from events you manually wire up;
alternatively, use the Storyboard to connect events which
can then be cleaned up automatically
Xamarin.iOS Tips

Android native application

Android Native Compilation
.dexfilesJava
compile
r
Android
dex
compiler
Java
bytecodes
Dalvik
bytecodes

Android Native Compilation
.dexfiles
Resources
(e.g.
images)
.apkfileAndroid
apkbuilde
r
The .apkfile contains
all the app's assets
and is ready to run

Android Native Execution
Bytecodes are compiled to
native code at installation
(called Ahead-of-Time or
AOT)
MyApp.apk
Android
Runtime
(ART)
Apps run in their own
process with their own
copy of the ART Virtual
Machine

DEMO ANDROID STUDIO

Xamarin.Android Architecture

Xamarin.Android Compilation
assemblyC#
compiler
IL and
metadata
Linke
r
Monoassemblies
yourassemblies
Monoassemblies
(filtered)
Determines which class members are used in
your app and includes only those members in
the output
yourassemblies
(filtered)

Xamarin.Android Compilation
Mono
Runtime
The Xamarin build tools
add the Mono VM to
your application
package
.apkfileAndroid
apkbuilde
r

DEMO XAMARIN.ANDROID

Xamarin.Android GC Process
GC
Collect
Can
collect
object?
Is
Peer
Object
?
Ye
s
Replace JNI
handle with
Weak Handle
Ye
s
Force Android GC
JNI
handle
collected
?
Collect object
No
Ye
s
Replace JNI
weak handle
with strong
handle reference
NoPeer
object
kept alive

• Integration between Xamarin GC and JVM GC is
performed through a native extension called the GC
Bridge
GC Bridge
Xamarin
Manage
d
Memory
Android
Manage
d
Memory
GC
Bridge
Process
Memor
y

• GC_ messages provide details about bridge and
collection times
Monitoring GC Performance
GC_MAJOR:(Minor allowance) pause 29.11ms, total 29.35ms, bridge 0.15msmajor
4048K/0K los 2766K/0K
Lower pause, bridge and total times are
preferred

• C# objects must be boxed to create a JVM
representation of the object; intrinsic types (strings,
numeric values and dates) are all special cased
Xamarin and the JAVA VM
C#
Object
Java
Object
ArrayAdapter<Tweet>
ArrayAdapter
ArrayLi
stTweet Tweet Tweet Tweet
Tweet Tweet Tweet Tweet
ListView

• Instead, do as much as possible in either C# or Java,
interop is expensive
Stay in your yard
C# Object
Java
Object
TweetAdapter
List<Tweet>
Tweet Tweet Tweet Tweet
ListView

Should call Dispose() to release the native resources
immediately (vs waiting on a GC) when you are finished
with a peer wrapper
Avoid placing a large numbers of references in peer
objects, remember GC is more expensive for these special
types
Avoid passing pure C# custom types into Java APIs if
possible
Xamarin.Android Tips

Xamarin
Process
Memory
UIView
UIImage
MKMapVie
w
...
Activity
Intent
TextView
...
Managed
Memory
C# and .NET
objects are
allocated here
- this is all GC
knows about

Q & A

Xamarin - Under the bridge

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Editor's Notes