Run runs a function on the main UI thread that requires access to an
Android activity. A nil activity is returned if none is available.

Signed-off-by: Greg Pomerantz <gmp.gio@wow.st>
---
 app/app.go                           |  7 -------
 app/app_android.go                   | 35 +++++++++++++++++++++++++++++++++++
 app/internal/window/GioActivity.java |  2 +-
 app/internal/window/GioView.java     | 28 +++++++++++++++++++++-------
 app/internal/window/handle.go        |  7 -------
 app/internal/window/os_android.c     | 11 ++++++++++-
 app/internal/window/os_android.go    | 27 +++++++++++++++++++++++++++
 app/internal/window/os_android.h     |  4 ++++
 8 files changed, 98 insertions(+), 23 deletions(-)
 create mode 100644 app/app_android.go
 delete mode 100644 app/internal/window/handle.go

diff --git a/app/app.go b/app/app.go
index 9a18ec4..71bc57b 100644
--- a/app/app.go
+++ b/app/app.go
@@ -9,13 +9,6 @@ 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
diff --git a/app/app_android.go b/app/app_android.go
new file mode 100644
index 0000000..b41bb43
--- /dev/null
+++ b/app/app_android.go
@@ -0,0 +1,35 @@
+package app
+
+import (
+	"gioui.org/app/internal/window"
+)
+
+type Handle window.Handle
+
+// PlatformHandle returns the Android platform-specific Handle.
+func PlatformHandle() *Handle {
+	return (*Handle)(window.PlatformHandle)
+}
+
+// JNIEnv is a struct wrapping a pointer to a JNI environment with an
+// underlying type of *C.JNIEnv.
+type JNIEnv struct {
+	JNIEnv uintptr
+}
+
+// Activity is a struct that wraps a pointer to an Android Activity with an
+// underlying type of C.jobject.
+type Activity struct {
+	Activity uintptr
+}
+
+// Run runs a function that needs access to the Android Activity for the
+// window. The function is run on the UI thread and should not block. The
+// function must be prepared to deal with a nil activity if none is
+// available. Run returns immediately and does not wait for the completion
+// of f.
+func (w *Window) Run(f func(env JNIEnv, activity Activity)) {
+	window.Run(w.driver, func(e, a uintptr) {
+		f(JNIEnv{e}, Activity{a})
+	})
+}
diff --git a/app/internal/window/GioActivity.java b/app/internal/window/GioActivity.java
index 2813d80..1a91f81 100644
--- a/app/internal/window/GioActivity.java
+++ b/app/internal/window/GioActivity.java
@@ -33,7 +33,7 @@ public class GioActivity extends Activity {
 
 	@Override public void onStart() {
 		super.onStart();
-		view.start();
+		view.start(this);
 	}
 
 	@Override public void onStop() {
diff --git a/app/internal/window/GioView.java b/app/internal/window/GioView.java
index 82bc36f..535ad58 100644
--- a/app/internal/window/GioView.java
+++ b/app/internal/window/GioView.java
@@ -2,6 +2,7 @@
 
 package org.gioui;
 
+import android.app.Activity;
 import android.content.Context;
 import android.graphics.Rect;
 import android.os.Build;
@@ -32,6 +33,7 @@ public class GioView extends SurfaceView implements Choreographer.FrameCallback
 	private final InputMethodManager imm;
 	private final Handler handler;
 	private long nhandle;
+	private Activity activity;
 
 	private static synchronized void initialize(Context appCtx) {
 		synchronized (initLock) {
@@ -51,18 +53,18 @@ public class GioView extends SurfaceView implements Choreographer.FrameCallback
 		}
 	}
 
-	public GioView(Context context) {
-		this(context, null);
+	public GioView(Activity activity) {
+		this(activity, null);
 	}
 
-	public GioView(Context context, AttributeSet attrs) {
-		super(context, attrs);
+	public GioView(Activity activity, AttributeSet attrs) {
+		super(activity, attrs);
 		// Late initialization of the Go runtime to wait for a valid context.
-		initialize(context.getApplicationContext());
+		initialize(activity.getApplicationContext());
 
 		nhandle = onCreateView(this);
 		handler = new Handler();
-		imm = (InputMethodManager)context.getSystemService(Context.INPUT_METHOD_SERVICE);
+		imm = (InputMethodManager)activity.getSystemService(Context.INPUT_METHOD_SERVICE);
 		setFocusable(true);
 		setFocusableInTouchMode(true);
 		setOnFocusChangeListener(new View.OnFocusChangeListener() {
@@ -181,15 +183,18 @@ public class GioView extends SurfaceView implements Choreographer.FrameCallback
 		return getResources().getConfiguration().fontScale;
 	}
 
-	void start() {
+	void start(Activity act) {
+		this.activity = act;
 		onStartView(nhandle);
 	}
 
 	void stop() {
+		this.activity = null;
 		onStopView(nhandle);
 	}
 
 	void destroy() {
+		this.activity = null;
 		getHolder().removeCallback(callbacks);
 		onDestroyView(nhandle);
 		nhandle = 0;
@@ -207,6 +212,14 @@ public class GioView extends SurfaceView implements Choreographer.FrameCallback
 		return onBack(nhandle);
 	}
 
+	public void Run(long funcPtr) {
+		handler.post(new Runnable() {
+			public void run() {
+				runCallback(activity, funcPtr);
+			}
+		});
+	}
+
 	static private native long onCreateView(GioView view);
 	static private native void onDestroyView(long handle);
 	static private native void onStartView(long handle);
@@ -222,6 +235,7 @@ public class GioView extends SurfaceView implements Choreographer.FrameCallback
 	static private native boolean onBack(long handle);
 	static private native void onFocusChange(long handle, boolean focus);
 	static private native void runGoMain(byte[] dataDir, Context context);
+	static private native void runCallback(Activity activity, long funcPtr);
 
 	private static class InputConnection extends BaseInputConnection {
 		private final Editable editable;
diff --git a/app/internal/window/handle.go b/app/internal/window/handle.go
deleted file mode 100644
index 5d7b1a1..0000000
--- a/app/internal/window/handle.go
@@ -1,7 +0,0 @@
-// +build !android
-
-package window
-
-var PlatformHandle *Handle
-
-type Handle struct{}
diff --git a/app/internal/window/os_android.c b/app/internal/window/os_android.c
index 5150ab6..b20ebea 100644
--- a/app/internal/window/os_android.c
+++ b/app/internal/window/os_android.c
@@ -94,7 +94,12 @@ JNIEXPORT jint JNI_OnLoad(JavaVM *vm, void *reserved) {
 			.name = "onFocusChange",
 			.signature = "(JZ)V",
 			.fnPtr = onFocusChange
-		}
+		},
+		{
+			.name = "runCallback",
+			.signature = "(Landroid/app/Activity;J)V",
+			.fnPtr = runCallback
+		},
 	};
 	if ((*env)->RegisterNatives(env, viewClass, methods, sizeof(methods)/sizeof(methods[0])) != 0) {
 		return -1;
@@ -166,3 +171,7 @@ void gio_jni_ReleaseByteArrayElements(JNIEnv *env, jbyteArray arr, jbyte *bytes)
 jsize gio_jni_GetArrayLength(JNIEnv *env, jbyteArray arr) {
 	return (*env)->GetArrayLength(env, arr);
 }
+
+void gio_jni_CallGioViewRun(JNIEnv *env, jobject view, jmethodID mid, runcb_t f) {
+	(*env)->CallVoidMethod(env, view, mid, (jlong)f);
+}
diff --git a/app/internal/window/os_android.go b/app/internal/window/os_android.go
index 5cce88d..693c3f3 100644
--- a/app/internal/window/os_android.go
+++ b/app/internal/window/os_android.go
@@ -54,6 +54,7 @@ type window struct {
 	mhideTextInput                 C.jmethodID
 	mpostFrameCallback             C.jmethodID
 	mpostFrameCallbackOnMainThread C.jmethodID
+	mRun                           C.jmethodID
 }
 
 var dataDirChan = make(chan string, 1)
@@ -99,6 +100,31 @@ func runGoMain(env *C.JNIEnv, class C.jclass, jdataDir C.jbyteArray, context C.j
 	runMain()
 }
 
+func Run(d Driver, f func(a, b uintptr)) {
+	if d == nil {
+		go f(0, 0)
+		return
+	}
+
+	// app/Window.Driver will always be a *window on Android, so this type-
+	// assertion is safe as long as Driver is not a nil interface.
+	w := d.(*window)
+
+	if w == nil {
+		go f(0, 0)
+		return
+	}
+	runInJVM(func(env *C.JNIEnv) {
+		C.gio_jni_CallGioViewRun(env, w.view, w.mRun, (*[0]byte)(unsafe.Pointer(&f)))
+	})
+}
+
+//export runCallback
+func runCallback(env *C.JNIEnv, class C.jclass, activity C.jobject, funcPtr C.runcb_t) {
+	f := (*func(a, b uintptr))(unsafe.Pointer(funcPtr))
+	(*f)(uintptr(unsafe.Pointer(env)), uintptr(unsafe.Pointer(activity)))
+}
+
 func GetDataDir() string {
 	return <-dataDirChan
 }
@@ -119,6 +145,7 @@ func onCreateView(env *C.JNIEnv, class C.jclass, view C.jobject) C.jlong {
 		mhideTextInput:                 jniGetMethodID(env, class, "hideTextInput", "()V"),
 		mpostFrameCallback:             jniGetMethodID(env, class, "postFrameCallback", "()V"),
 		mpostFrameCallbackOnMainThread: jniGetMethodID(env, class, "postFrameCallbackOnMainThread", "()V"),
+		mRun:                           jniGetMethodID(env, class, "Run", "(J)V"),
 	}
 	wopts := <-mainWindow.out
 	w.callbacks = wopts.window
diff --git a/app/internal/window/os_android.h b/app/internal/window/os_android.h
index 288d633..a31ec4b 100644
--- a/app/internal/window/os_android.h
+++ b/app/internal/window/os_android.h
@@ -17,3 +17,7 @@ __attribute__ ((visibility ("hidden"))) void gio_jni_CallVoidMethod_J(JNIEnv *en
 __attribute__ ((visibility ("hidden"))) jbyte *gio_jni_GetByteArrayElements(JNIEnv *env, jbyteArray arr);
 __attribute__ ((visibility ("hidden"))) void gio_jni_ReleaseByteArrayElements(JNIEnv *env, jbyteArray arr, jbyte *bytes);
 __attribute__ ((visibility ("hidden"))) jsize gio_jni_GetArrayLength(JNIEnv *env, jbyteArray arr);
+
+typedef void (*runcb_t)(JNIEnv *env, jobject activity);
+
+void gio_jni_CallGioViewRun(JNIEnv *env, jobject view, jmethodID mid, runcb_t f);
-- 
2.16.2