app: add Handle type and PlatformHandle()

On Android, allow access to JVM and Application context.

Signed-off-by: Greg Pomerantz <gmp.gio@wow.st>

app/app.go

@@ -9,6 +9,13 @@ import (
 	"gioui.org/app/internal/window"
 )
 
+type Handle window.Handle
+
+// PlatformHandle returns the platform specific Handle.
+func PlatformHandle() *Handle {
+	return (*Handle)(window.PlatformHandle)
+}
+
 // extraArgs contains extra arguments to append to
 // os.Args. The arguments are separated with |.
 // Useful for running programs on mobiles where the

app/internal/window/GioView.java

@@ -46,7 +46,7 @@ public class GioView extends SurfaceView implements Choreographer.FrameCallback
 				throw new RuntimeException(e);
 			}
 			System.loadLibrary("gio");
-			runGoMain(dataDirUTF8);
+			runGoMain(dataDirUTF8, appCtx);
 			jniLoaded = true;
 		}
 	}
@@ -219,7 +219,7 @@ public class GioView extends SurfaceView implements Choreographer.FrameCallback
 	static private native void onFrameCallback(long handle, long nanos);
 	static private native boolean onBack(long handle);
 	static private native void onFocusChange(long handle, boolean focus);
-	static private native void runGoMain(byte[] dataDir);
+	static private native void runGoMain(byte[] dataDir, Context context);
 
 	private static class InputConnection extends BaseInputConnection {
 		private final Editable editable;

app/internal/window/handle.go

@@ -0,0 +1,7 @@
+// +build !android
+
+package window
+
+var PlatformHandle *Handle
+
+type Handle struct{}

app/internal/window/handle_android.go

@@ -0,0 +1,11 @@
+package window
+
+var PlatformHandle *Handle
+
+type Handle struct {
+	// JVM is the JNI *JVM pointer.
+	JVM uintptr
+	// Context is a global reference to the application's
+	// android.content.Context instance.
+	Context uintptr
+}

app/internal/window/os_android.c

@@ -22,7 +22,7 @@ JNIEXPORT jint JNI_OnLoad(JavaVM *vm, void *reserved) {
 	static const JNINativeMethod methods[] = {
 		{
 			.name = "runGoMain",
-			.signature = "([B)V",
+			.signature = "([BLandroid/content/Context;)V",
 			.fnPtr = runGoMain
 		},
 		{

app/internal/window/os_android.go

@@ -80,7 +80,7 @@ func jniGetStaticMethodID(env *C.JNIEnv, class C.jclass, method, sig string) C.j
 }
 
 //export runGoMain
-func runGoMain(env *C.JNIEnv, class C.jclass, jdataDir C.jbyteArray) {
+func runGoMain(env *C.JNIEnv, class C.jclass, jdataDir C.jbyteArray, context C.jobject) {
 	dirBytes := C.gio_jni_GetByteArrayElements(env, jdataDir)
 	if dirBytes == nil {
 		panic("runGoMain: GetByteArrayElements failed")
@@ -89,6 +89,12 @@ func runGoMain(env *C.JNIEnv, class C.jclass, jdataDir C.jbyteArray) {
 	dataDir := C.GoStringN((*C.char)(unsafe.Pointer(dirBytes)), n)
 	dataDirChan <- dataDir
 	C.gio_jni_ReleaseByteArrayElements(env, jdataDir, dirBytes)
+	context = C.gio_jni_NewGlobalRef(env, context)
+
+	PlatformHandle = &Handle{
+		JVM:     uintptr(unsafe.Pointer(theJVM)),
+		Context: uintptr(context),
+	}
 	runMain()
 }