Get android notifications working.

It's kindof MVP and could do with improvements, but it works down to API 16

app/app_mobile_and.c

@@ -0,0 +1,81 @@
+// +build !ci
+
+// +build android
+
+#include <android/log.h>
+#include <jni.h>
+#include <stdlib.h>
+
+#define LOG_FATAL(...) __android_log_print(ANDROID_LOG_FATAL, "GoLog", __VA_ARGS__)
+
+static jclass find_class(JNIEnv *env, const char *class_name) {
+	jclass clazz = (*env)->FindClass(env, class_name);
+	if (clazz == NULL) {
+		(*env)->ExceptionClear(env);
+		LOG_FATAL("cannot find %s", class_name);
+		return NULL;
+	}
+	return clazz;
+}
+
+static jmethodID find_method(JNIEnv *env, jclass clazz, const char *name, const char *sig) {
+	jmethodID m = (*env)->GetMethodID(env, clazz, name, sig);
+	if (m == 0) {
+		(*env)->ExceptionClear(env);
+		LOG_FATAL("cannot find method %s %s", name, sig);
+		return 0;
+	}
+	return m;
+}
+
+static jmethodID find_static_method(JNIEnv *env, jclass clazz, const char *name, const char *sig) {
+	jmethodID m = (*env)->GetStaticMethodID(env, clazz, name, sig);
+	if (m == 0) {
+		(*env)->ExceptionClear(env);
+		LOG_FATAL("cannot find method %s %s", name, sig);
+		return 0;
+	}
+	return m;
+}
+
+jobject getSystemService(uintptr_t jni_env, uintptr_t ctx, char *service) {
+	JNIEnv *env = (JNIEnv*)jni_env;
+	jstring serviceStr = (*env)->NewStringUTF(env, service);
+
+	jclass ctxClass = (*env)->GetObjectClass(env, ctx);
+	jmethodID getSystemService = find_method(env, ctxClass, "getSystemService", "(Ljava/lang/String;)Ljava/lang/Object;");
+
+	return (jobject)(*env)->CallObjectMethod(env, ctx, getSystemService, serviceStr);
+}
+
+int nextId = 1;
+
+void sendNotification(uintptr_t java_vm, uintptr_t jni_env, uintptr_t ctx, char *title, char *body) {
+	JNIEnv *env = (JNIEnv*)jni_env;
+	jstring titleStr = (*env)->NewStringUTF(env, title);
+	jstring bodyStr = (*env)->NewStringUTF(env, body);
+
+	jclass cls = find_class(env, "android/app/Notification$Builder");
+	jmethodID constructor = find_method(env, cls, "<init>", "(Landroid/content/Context;)V");
+	jobject builder = (*env)->NewObject(env, cls, constructor, ctx);
+
+	jmethodID setContentTitle = find_method(env, cls, "setContentTitle", "(Ljava/lang/CharSequence;)Landroid/app/Notification$Builder;");
+	(*env)->CallObjectMethod(env, builder, setContentTitle, titleStr);
+
+	jmethodID setContentText = find_method(env, cls, "setContentText", "(Ljava/lang/CharSequence;)Landroid/app/Notification$Builder;");
+    (*env)->CallObjectMethod(env, builder, setContentText, bodyStr);
+
+    int iconID = 17629184; // constant of "unknown app icon"
+	jmethodID setSmallIcon = find_method(env, cls, "setSmallIcon", "(I)Landroid/app/Notification$Builder;");
+    (*env)->CallObjectMethod(env, builder, setSmallIcon, iconID);
+
+	jmethodID build = find_method(env, cls, "build", "()Landroid/app/Notification;");
+    jobject notif = (*env)->CallObjectMethod(env, builder, build);
+
+	jclass mgrCls = find_class(env, "android/app/NotificationManager");
+    jobject mgr = getSystemService(env, ctx, "notification");
+
+	jmethodID notify = find_method(env, mgrCls, "notify", "(ILandroid/app/Notification;)V");
+    (*env)->CallVoidMethod(env, mgr, notify, nextId, notif);
+    nextId++;
+}

app/app_mobile_and.go

@@ -4,10 +4,21 @@
 
 package app
 
+/*
+#cgo LDFLAGS: -landroid -llog
+
+#include <stdlib.h>
+
+void sendNotification(uintptr_t java_vm, uintptr_t jni_env, uintptr_t ctx, char *title, char *content);
+*/
+import "C"
 import (
 	"log"
 	"net/url"
 	"os"
+	"unsafe"
+
+	mobileApp "github.com/fyne-io/mobile/app"
 
 	"fyne.io/fyne"
 	"fyne.io/fyne/theme"
@@ -25,7 +36,15 @@ func (app *fyneApp) OpenURL(url *url.URL) error {
 }
 
 func (app *fyneApp) SendNotification(notify *fyne.Notification) {
-	log.Println("NOT YET IMPLEMENTED") // TODO
+	titleStr := C.CString(notify.Title)
+	defer C.free(unsafe.Pointer(titleStr))
+	contentStr := C.CString(notify.Content)
+	defer C.free(unsafe.Pointer(contentStr))
+
+	mobileApp.RunOnJVM(func(vm, env, ctx uintptr) error {
+		C.sendNotification(C.uintptr_t(vm), C.uintptr_t(env), C.uintptr_t(ctx), titleStr, contentStr)
+		return nil
+	})
 }
 
 func rootConfigDir() string {

cmd/fyne/internal/mobile/binres/binres.go

@@ -281,7 +281,7 @@ func UnmarshalXML(r io.Reader, withIcon bool) (*XML, error) {
 									Space: androidSchema,
 									Local: "targetSdkVersion",
 								},
-								Value: "28",
+								Value: "25",
 							},
 						},
 					}