github.com/SahandAslani/gomobile@v0.0.0-20210909130135-2cb2d44c09b2/asset/asset_android.go (about)

     1  // Copyright 2015 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package asset
     6  
     7  /*
     8  #cgo LDFLAGS: -landroid
     9  #include <android/asset_manager.h>
    10  #include <android/asset_manager_jni.h>
    11  #include <jni.h>
    12  #include <stdlib.h>
    13  
    14  static AAssetManager* asset_manager_init(uintptr_t java_vm, uintptr_t jni_env, jobject ctx) {
    15  	JavaVM* vm = (JavaVM*)java_vm;
    16  	JNIEnv* env = (JNIEnv*)jni_env;
    17  
    18  	// Equivalent to:
    19  	//	assetManager = ctx.getResources().getAssets();
    20  	jclass ctx_clazz = (*env)->FindClass(env, "android/content/Context");
    21  	jmethodID getres_id = (*env)->GetMethodID(env, ctx_clazz, "getResources", "()Landroid/content/res/Resources;");
    22  	jobject res = (*env)->CallObjectMethod(env, ctx, getres_id);
    23  	jclass res_clazz = (*env)->FindClass(env, "android/content/res/Resources");
    24  	jmethodID getam_id = (*env)->GetMethodID(env, res_clazz, "getAssets", "()Landroid/content/res/AssetManager;");
    25  	jobject am = (*env)->CallObjectMethod(env, res, getam_id);
    26  
    27  	// Pin the AssetManager and load an AAssetManager from it.
    28  	am = (*env)->NewGlobalRef(env, am);
    29  	return AAssetManager_fromJava(env, am);
    30  }
    31  */
    32  import "C"
    33  import (
    34  	"fmt"
    35  	"io"
    36  	"log"
    37  	"os"
    38  	"sync"
    39  	"unsafe"
    40  
    41  	"github.com/SahandAslani/gomobile/internal/mobileinit"
    42  )
    43  
    44  var assetOnce sync.Once
    45  
    46  // asset_manager is the asset manager of the app.
    47  var assetManager *C.AAssetManager
    48  
    49  func assetInit() {
    50  	err := mobileinit.RunOnJVM(func(vm, env, ctx uintptr) error {
    51  		assetManager = C.asset_manager_init(C.uintptr_t(vm), C.uintptr_t(env), C.jobject(ctx))
    52  		return nil
    53  	})
    54  	if err != nil {
    55  		log.Fatalf("asset: %v", err)
    56  	}
    57  }
    58  
    59  func openAsset(name string) (File, error) {
    60  	assetOnce.Do(assetInit)
    61  	cname := C.CString(name)
    62  	defer C.free(unsafe.Pointer(cname))
    63  	a := &asset{
    64  		ptr:  C.AAssetManager_open(assetManager, cname, C.AASSET_MODE_UNKNOWN),
    65  		name: name,
    66  	}
    67  	if a.ptr == nil {
    68  		return nil, a.errorf("open", "bad asset")
    69  	}
    70  	return a, nil
    71  }
    72  
    73  type asset struct {
    74  	ptr  *C.AAsset
    75  	name string
    76  }
    77  
    78  func (a *asset) errorf(op string, format string, v ...interface{}) error {
    79  	return &os.PathError{
    80  		Op:   op,
    81  		Path: a.name,
    82  		Err:  fmt.Errorf(format, v...),
    83  	}
    84  }
    85  
    86  func (a *asset) Read(p []byte) (n int, err error) {
    87  	n = int(C.AAsset_read(a.ptr, unsafe.Pointer(&p[0]), C.size_t(len(p))))
    88  	if n == 0 && len(p) > 0 {
    89  		return 0, io.EOF
    90  	}
    91  	if n < 0 {
    92  		return 0, a.errorf("read", "negative bytes: %d", n)
    93  	}
    94  	return n, nil
    95  }
    96  
    97  func (a *asset) Seek(offset int64, whence int) (int64, error) {
    98  	// TODO(crawshaw): use AAsset_seek64 if it is available.
    99  	off := C.AAsset_seek(a.ptr, C.off_t(offset), C.int(whence))
   100  	if off == -1 {
   101  		return 0, a.errorf("seek", "bad result for offset=%d, whence=%d", offset, whence)
   102  	}
   103  	return int64(off), nil
   104  }
   105  
   106  func (a *asset) Close() error {
   107  	C.AAsset_close(a.ptr)
   108  	return nil
   109  }