解释
示例代码展示了如何存储 2 个不同的位图（小的，但它只是一个演示），回收原始的 java 的，然后将它们恢复到 java 实例并使用它们。
正如您可能猜到的那样，该布局有 2 个 imageViews。我没有将它包含在代码中，因为它很明显。
如果需要，请记住将代码更改为您自己的包，否则将无法正常工作。
MainActivity.java - 如何使用：
package com.example.jnibitmapstoragetest;
...
public class MainActivity extends Activity
{
@Override
protected void onCreate(final Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
//
Bitmap bitmap=BitmapFactory.decodeResource(getResources(),R.drawable.ic_launcher);
final JniBitmapHolder bitmapHolder=new JniBitmapHolder(bitmap);
bitmap.recycle();
//
Bitmap bitmap2=BitmapFactory.decodeResource(getResources(),android.R.drawable.sym_action_call);
final JniBitmapHolder bitmapHolder2=new JniBitmapHolder(bitmap2);
bitmap2.recycle();
//
setContentView(R.layout.activity_main);
{
bitmap=bitmapHolder.getBitmapAndFree();
final ImageView imageView=(ImageView)findViewById(R.id.imageView1);
imageView.setImageBitmap(bitmap);
}
{
bitmap2=bitmapHolder2.getBitmapAndFree();
final ImageView imageView=(ImageView)findViewById(R.id.imageView2);
imageView.setImageBitmap(bitmap2);
}
}
}
JniBitmapHolder.java - JNI 和 JAVA 之间的“桥梁”：
package com.example.jnibitmapstoragetest;
...
public class JniBitmapHolder
{
ByteBuffer _handler =null;
static
{
System.loadLibrary("JniBitmapStorageTest");
}
private native ByteBuffer jniStoreBitmapData(Bitmap bitmap);
private native Bitmap jniGetBitmapFromStoredBitmapData(ByteBuffer handler);
private native void jniFreeBitmapData(ByteBuffer handler);
public JniBitmapHolder()
{}
public JniBitmapHolder(final Bitmap bitmap)
{
storeBitmap(bitmap);
}
public void storeBitmap(final Bitmap bitmap)
{
if(_handler!=null)
freeBitmap();
_handler=jniStoreBitmapData(bitmap);
}
public Bitmap getBitmap()
{
if(_handler==null)
return null;
return jniGetBitmapFromStoredBitmapData(_handler);
}
public Bitmap getBitmapAndFree()
{
final Bitmap bitmap=getBitmap();
freeBitmap();
return bitmap;
}
public void freeBitmap()
{
if(_handler==null)
return;
jniFreeBitmapData(_handler);
_handler=null;
}
@Override
protected void finalize() throws Throwable
{
super.finalize();
if(_handler==null)
return;
Log.w("DEBUG","JNI bitmap wasn't freed nicely.please rememeber to free the bitmap as soon as you can");
freeBitmap();
}
}
Android.mk - JNI 的属性文件：
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := JniBitmapStorageTest
LOCAL_SRC_FILES := JniBitmapStorageTest.cpp
LOCAL_LDLIBS := -llog
LOCAL_LDFLAGS += -ljnigraphics
include $(BUILD_SHARED_LIBRARY)
APP_OPTIM := debug
LOCAL_CFLAGS := -g
JniBitmapStorageTest.cpp - “神奇”的东西在这里：
#include <jni.h>
#include <jni.h>
#include <android/log.h>
#include <stdio.h>
#include <android/bitmap.h>
#include <cstring>
#include <unistd.h>
#define LOG_TAG "DEBUG"
#define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG,LOG_TAG,__VA_ARGS__)
#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,__VA_ARGS__)
extern "C"
{
JNIEXPORT jobject JNICALL Java_com_example_jnibitmapstoragetest_JniBitmapHolder_jniStoreBitmapData(JNIEnv * env, jobject obj, jobject bitmap);
JNIEXPORT jobject JNICALL Java_com_example_jnibitmapstoragetest_JniBitmapHolder_jniGetBitmapFromStoredBitmapData(JNIEnv * env, jobject obj, jobject handle);
JNIEXPORT void JNICALL Java_com_example_jnibitmapstoragetest_JniBitmapHolder_jniFreeBitmapData(JNIEnv * env, jobject obj, jobject handle);
}
class JniBitmap
{
public:
uint32_t* _storedBitmapPixels;
AndroidBitmapInfo _bitmapInfo;
JniBitmap()
{
_storedBitmapPixels = NULL;
}
};
JNIEXPORT void JNICALL Java_com_example_jnibitmapstoragetest_JniBitmapHolder_jniFreeBitmapData(JNIEnv * env, jobject obj, jobject handle)
{
JniBitmap* jniBitmap = (JniBitmap*) env->GetDirectBufferAddress(handle);
if (jniBitmap->_storedBitmapPixels == NULL)
return;
delete[] jniBitmap->_storedBitmapPixels;
jniBitmap->_storedBitmapPixels = NULL;
delete jniBitmap;
}
JNIEXPORT jobject JNICALL Java_com_example_jnibitmapstoragetest_JniBitmapHolder_jniGetBitmapFromStoredBitmapData(JNIEnv * env, jobject obj, jobject handle)
{
JniBitmap* jniBitmap = (JniBitmap*) env->GetDirectBufferAddress(handle);
if (jniBitmap->_storedBitmapPixels == NULL)
{
LOGD("no bitmap data was stored. returning null...");
return NULL;
}
//
//creating a new bitmap to put the pixels into it - using Bitmap Bitmap.createBitmap (int width, int height, Bitmap.Config config) :
//
//LOGD("creating new bitmap...");
jclass bitmapCls = env->FindClass("android/graphics/Bitmap");
jmethodID createBitmapFunction = env->GetStaticMethodID(bitmapCls, "createBitmap", "(IILandroid/graphics/Bitmap$Config;)Landroid/graphics/Bitmap;");
jstring configName = env->NewStringUTF("ARGB_8888");
jclass bitmapConfigClass = env->FindClass("android/graphics/Bitmap$Config");
jmethodID valueOfBitmapConfigFunction = env->GetStaticMethodID(bitmapConfigClass, "valueOf", "(Ljava/lang/String;)Landroid/graphics/Bitmap$Config;");
jobject bitmapConfig = env->CallStaticObjectMethod(bitmapConfigClass, valueOfBitmapConfigFunction, configName);
jobject newBitmap = env->CallStaticObjectMethod(bitmapCls, createBitmapFunction, jniBitmap->_bitmapInfo.height, jniBitmap->_bitmapInfo.width, bitmapConfig);
//
// putting the pixels into the new bitmap:
//
int ret;
void* bitmapPixels;
if ((ret = AndroidBitmap_lockPixels(env, newBitmap, &bitmapPixels)) < 0)
{
LOGE("AndroidBitmap_lockPixels() failed ! error=%d", ret);
return NULL;
}
uint32_t* newBitmapPixels = (uint32_t*) bitmapPixels;
int pixelsCount = jniBitmap->_bitmapInfo.height * jniBitmap->_bitmapInfo.width;
memcpy(newBitmapPixels, jniBitmap->_storedBitmapPixels, sizeof(uint32_t) * pixelsCount);
AndroidBitmap_unlockPixels(env, newBitmap);
//LOGD("returning the new bitmap");
return newBitmap;
}
JNIEXPORT jobject JNICALL Java_com_example_jnibitmapstoragetest_JniBitmapHolder_jniStoreBitmapData(JNIEnv * env, jobject obj, jobject bitmap)
{
AndroidBitmapInfo bitmapInfo;
uint32_t* storedBitmapPixels = NULL;
//LOGD("reading bitmap info...");
int ret;
if ((ret = AndroidBitmap_getInfo(env, bitmap, &bitmapInfo)) < 0)
{
LOGE("AndroidBitmap_getInfo() failed ! error=%d", ret);
return NULL;
}
LOGD("width:%d height:%d stride:%d", bitmapInfo.width, bitmapInfo.height, bitmapInfo.stride);
if (bitmapInfo.format != ANDROID_BITMAP_FORMAT_RGBA_8888)
{
LOGE("Bitmap format is not RGBA_8888!");
return NULL;
}
//
//read pixels of bitmap into native memory :
//
//LOGD("reading bitmap pixels...");
void* bitmapPixels;
if ((ret = AndroidBitmap_lockPixels(env, bitmap, &bitmapPixels)) < 0)
{
LOGE("AndroidBitmap_lockPixels() failed ! error=%d", ret);
return NULL;
}
uint32_t* src = (uint32_t*) bitmapPixels;
storedBitmapPixels = new uint32_t[bitmapInfo.height * bitmapInfo.width];
int pixelsCount = bitmapInfo.height * bitmapInfo.width;
memcpy(storedBitmapPixels, src, sizeof(uint32_t) * pixelsCount);
AndroidBitmap_unlockPixels(env, bitmap);
JniBitmap *jniBitmap = new JniBitmap();
jniBitmap->_bitmapInfo = bitmapInfo;
jniBitmap->_storedBitmapPixels = storedBitmapPixels;
return env->NewDirectByteBuffer(jniBitmap, 0);
}