How do i - create a native interface

What’s a Native Interface?
✦Native interfaces allow us to invoke OS native code
✦We can use it directly in the app or wrap it in a library
(cn1lib) for a common abstraction
✦Native in Codename One is diﬀerent from native in Java.
In Java native is always C, in Codename one it’s
something else
© Codename One 2017 all rights reserved

Native in Codename One
✦Android - Java (Dalvik/Art) code, you can still wrap
NDK code with AAR
✦iOS - Objective-C code and native libraries
✦Windows - C# code
✦JavaScript - JavaScript code
✦Desktop Port - Java SE code

package com.codename1.app.nativedemo;
import com.codename1.system.NativeInterface;
public interface CallNativeCode extends NativeInterface {
public String doThisInNative(String arg1, int arg2);
}
Hello World Native Interface

Generate Native Interface
✦The Generate Native Access action automatically
generates required native code stubs
✦Stubs will appear under the “native” directory

public class CallNativeCodeImpl {
public String doThisInNative(String param, int param1) {
return null;
}
public boolean isSupported() {
return false;
}
}
Android Stub

public class CallNativeCodeImpl {
public String doThisInNative(String param, int param1) {
return "Dummy";
}
public boolean isSupported() {
return true;
}
}
Android Implementation

#import "com_codename1_app_nativedemo_CallNativeCodeImpl.h"
@implementation com_codename1_app_nativedemo_CallNativeCodeImpl
-(NSString*)doThisInNative:(NSString*)param param1:(int)param1{
return nil;
}
-(BOOL)isSupported{
return NO;
}
@end
iOS Stub

#import "com_codename1_app_nativedemo_CallNativeCodeImpl.h"
@implementation com_codename1_app_nativedemo_CallNativeCodeImpl
-(NSString*)doThisInNative:(NSString*)param param1:(int)param1{
return @"Dummy";
}
-(BOOL)isSupported{
return YES;
}
@end
iOS Implementation

namespace com.codename1.app.nativedemo{
public class CallNativeCodeImpl : ICallNativeCodeImpl {
public string doThisInNative(String param, int param1) {
return null;
}
public bool isSupported() {
return false;
}
}
}
Windows Stub

CallNativeCode cn = NativeLookup.create(CallNativeCode.class);
if(cn != null && cn.isSupported()) {
String returnVal = cn.doThisInNative("String", 1);
}
Using the Code

Implementation
✦Code doesn’t compile on the client & won’t have code
completion
✦A neat trick is using “include source” and then opening
the native source in xcode or Android Studio and
implementing the native code there
✦You can’t use all types. You can’t pass objects!
✦Use PeerComponent to represent a native UI widget
✦You can use callbacks from the native code

Build Hints
✦You can use build hints to inject many native interface
behaviors
✦Native code on Android often requires a 3rd party library
thru gradle, native code on iOS often uses cocoapods
we support both thru build hints
✦You can inject values into the manifest or plist to make
use of this
✦You can look thru existing cn1libs for sample code

How do i - create a native interface

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