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August 12, 2025 21:16
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| //go:generate javac -classpath $ANDROID_HOME/platforms/android-36/android.jar -d /tmp/java_classes Utils.java | |
| //go:generate jar cf Utils.jar -C /tmp/java_classes . | |
| package main | |
| /* | |
| #cgo LDFLAGS: -llog -landroid | |
| #include <android/log.h> | |
| #include <android/native_window_jni.h> | |
| #include <stdlib.h> | |
| static jint jni_GetEnvOrAttach(JavaVM *vm, JNIEnv **env, jint *attached) { | |
| jint res = (*vm)->GetEnv(vm, (void **)env, JNI_VERSION_1_6); | |
| if (res == JNI_EDETACHED) { | |
| res = (*vm)->AttachCurrentThread(vm, (void **)env, NULL); | |
| *attached = res == JNI_OK; | |
| } | |
| return res; | |
| } | |
| static void jni_DetachCurrent(JavaVM *vm) { | |
| (*vm)->DetachCurrentThread(vm); | |
| } | |
| */ | |
| import "C" | |
| import ( | |
| "fmt" | |
| "log" | |
| "os" | |
| "runtime" | |
| "runtime/debug" | |
| "strings" | |
| "unsafe" | |
| "gioui.org/app" | |
| "gioui.org/font/gofont" | |
| "gioui.org/op" | |
| "gioui.org/text" | |
| "gioui.org/widget/material" | |
| "github.com/timob/jnigi" | |
| ) | |
| func getJNIEnv() (*jnigi.Env, func()) { | |
| runtime.LockOSThread() | |
| jvm := app.JavaVM() | |
| cJVM := (*C.JavaVM)(unsafe.Pointer(jvm)) | |
| var cEnv *C.JNIEnv | |
| var attached C.jint | |
| C.jni_GetEnvOrAttach(cJVM, &cEnv, &attached) | |
| _, env := jnigi.UseJVM(unsafe.Pointer(jvm), unsafe.Pointer(cEnv), nil) | |
| cleanup := func() { | |
| if attached != 0 { | |
| C.jni_DetachCurrent(cJVM) | |
| } | |
| runtime.UnlockOSThread() | |
| } | |
| return env, cleanup | |
| } | |
| func writeToDownloadsFolder(filename, mimetype string, contents []byte) error { | |
| env, cleanup := getJNIEnv() | |
| defer cleanup() | |
| context := jnigi.WrapJObject(app.AppContext(), "android/content/Context", false) | |
| filenameObj, err := env.NewObject("java/lang/String", []byte(filename)) | |
| if err != nil { | |
| return err | |
| } | |
| mimetypeObj, err := env.NewObject("java/lang/String", []byte(mimetype)) | |
| if err != nil { | |
| return err | |
| } | |
| contentsObj := env.NewByteArrayFromSlice(contents) | |
| err = env.CallStaticMethod( | |
| "com/example/demo/Utils", | |
| "writeToDownloadsFolder", | |
| nil, // returns void | |
| context, contentsObj, filenameObj, mimetypeObj, | |
| ) | |
| return err | |
| } | |
| func androidCrashHandler() { | |
| if r := recover(); r != nil { | |
| str := fmt.Sprintf("Crash: %v\n%s", r, debug.Stack()) | |
| tag := C.CString("demo-project") | |
| defer C.free(unsafe.Pointer(tag)) | |
| lines := strings.Split(str, "\n") | |
| for _, line := range lines { | |
| msg := C.CString(line) | |
| C.__android_log_write(C.ANDROID_LOG_INFO, tag, msg) // from <android/log.h> | |
| C.free(unsafe.Pointer(msg)) | |
| } | |
| } | |
| } | |
| func main() { | |
| if runtime.GOOS == "android" { | |
| defer androidCrashHandler() | |
| contents := []byte("Open your mind...") | |
| if err := writeToDownloadsFolder("this-works.txt", "text/plain", contents); err != nil { | |
| panic(fmt.Sprintf("Failed to write to Downloads: %s", err)) | |
| } | |
| } | |
| go func() { | |
| w := new(app.Window) | |
| if err := loop(w); err != nil { | |
| log.Fatal(err) | |
| } | |
| os.Exit(0) | |
| }() | |
| app.Main() | |
| } | |
| func loop(w *app.Window) error { | |
| th := material.NewTheme() | |
| th.Shaper = text.NewShaper(text.WithCollection(gofont.Collection())) | |
| var ops op.Ops | |
| for { | |
| switch e := w.Event().(type) { | |
| case app.DestroyEvent: | |
| return e.Err | |
| case app.FrameEvent: | |
| gtx := app.NewContext(&ops, e) | |
| l := material.H1(th, "Hello world!") | |
| l.Alignment = text.Middle | |
| l.Layout(gtx) | |
| e.Frame(gtx.Ops) | |
| } | |
| } | |
| } |
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| package com.example.demo; | |
| import android.content.ContentResolver; | |
| import android.content.ContentValues; | |
| import android.content.Context; | |
| import android.net.Uri; | |
| import android.os.Environment; | |
| import android.provider.MediaStore; | |
| import android.util.Log; | |
| import java.io.OutputStream; | |
| public class Utils { | |
| public static void writeToDownloadsFolder( | |
| Context context, byte[] contents, String filename, String mimetype) { | |
| try { | |
| ContentResolver resolver = context.getContentResolver(); | |
| ContentValues values = new ContentValues(); | |
| values.put(MediaStore.MediaColumns.DISPLAY_NAME, filename); | |
| values.put(MediaStore.MediaColumns.MIME_TYPE, mimetype); | |
| values.put(MediaStore.MediaColumns.RELATIVE_PATH, | |
| Environment.DIRECTORY_DOWNLOADS + "/"); | |
| Uri uri = resolver.insert(MediaStore.Files.getContentUri("external"), values); | |
| OutputStream output = resolver.openOutputStream(uri); | |
| output.write(contents); | |
| output.flush(); | |
| output.close(); | |
| } catch (Exception e) { | |
| Log.e("demo-project", "Exception occurred!", e); | |
| } | |
| } | |
| } |
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