修改Android 4.2.2的原生Camera引出的java.lang.UnsatisfiedLinkError: Native method not found，及解决方法

修改Android 4.2.2的原生Camera应用，做一些定制，将Camera的包名从之前的 package com.android.* 修改成了com.zhao3546.*。

调整后，应用可以正常运行，但是Camera自带的特效编辑等功能，无法正常使用。一点图片编辑的图标，就出现了下面的异常：

09-12 18:52:48.131: E/AndroidRuntime(6071): java.lang.UnsatisfiedLinkError: Native method not found: com.zhao3546.gallery3d.filtershow.filters.ImageFilterFx.nativeApplyFilter:(Landroid/graphics/Bitmap;IILandroid/graphics/Bitmap;II)V
09-12 18:52:48.131: E/AndroidRuntime(6071): 	at com.zhao3546.gallery3d.filtershow.filters.ImageFilterFx.nativeApplyFilter(Native Method)
09-12 18:52:48.131: E/AndroidRuntime(6071): 	at com.zhao3546.gallery3d.filtershow.filters.ImageFilterFx.apply(ImageFilterFx.java:58)
09-12 18:52:48.131: E/AndroidRuntime(6071): 	at com.zhao3546.gallery3d.filtershow.presets.ImagePreset.apply(ImagePreset.java:291)
09-12 18:52:48.131: E/AndroidRuntime(6071): 	at com.zhao3546.gallery3d.filtershow.cache.DirectPresetCache.compute(DirectPresetCache.java:156)
09-12 18:52:48.131: E/AndroidRuntime(6071): 	at com.zhao3546.gallery3d.filtershow.cache.DelayedPresetCache.handleMessage(DelayedPresetCache.java:50)

原来，ImageFilterFx.nativeApplyFilter() 的这个方法是通过JNI实现的，想想也是，不使用JNI的话，使用Java实现图片编辑的特效，效率要低不少。

关于JNI的介绍，个人觉得写得最好的是《Android框架揭秘》这本书的 “第四章 JNI和NDK”，从示例出发，再将原理娓娓道来，很深入浅出。

言归正传，看看怎么解决吧。

如下是根据 nativeApplyFilter 关键字搜索，找到的结果如下，只保留一小部分：

---- nativeApplyFilter Matches (55 in 30 files) ----
Bw.c (jni\filters):void JNIFUNCF(ImageFilterBW, nativeApplyFilter, jobject bitmap, jint width, jint height)
Bw.c (jni\filters):void JNIFUNCF(ImageFilterBWRed, nativeApplyFilter, jobject bitmap, jint width, jint height)
Bw.c (jni\filters):void JNIFUNCF(ImageFilterBWGreen, nativeApplyFilter, jobject bitmap, jint width, jint height)
Bw.c (jni\filters):void JNIFUNCF(ImageFilterBWBlue, nativeApplyFilter, jobject bitmap, jint width, jint height)
Bwfilter.c (jni\filters):void JNIFUNCF(ImageFilterBwFilter, nativeApplyFilter, jobject bitmap, jint width, jint height, jint rw, jint gw, jint bw)
Contrast.c (jni\filters):void JNIFUNCF(ImageFilterContrast, nativeApplyFilter, jobject bitmap, jint width, jint height, jfloat bright)
Exposure.c (jni\filters):void JNIFUNCF(ImageFilterExposure, nativeApplyFilter, jobject bitmap, jint width, jint height, jfloat bright)
Fx.c (jni\filters):void JNIFUNCF(ImageFilterFx, nativeApplyFilter, jobject bitmap, jint width, jint height, jobject lutbitmap,jint lutwidth, jint lutheight )
Geometry.c (jni\filters):void JNIFUNCF(ImageFilterGeometry, nativeApplyFilterFlip, jobject src, jint srcWidth, jint srcHeight, jobject dst, jint dstWidth, jint dstHeight, jint flip) {
Geometry.c (jni\filters):void JNIFUNCF(ImageFilterGeometry, nativeApplyFilterRotate, jobject src, jint srcWidth, jint srcHeight, jobject dst, jint dstWidth, jint dstHeight, jint rotate) {
Geometry.c (jni\filters):void JNIFUNCF(ImageFilterGeometry, nativeApplyFilterCrop, jobject src, jint srcWidth, jint srcHeight, jobject dst, jint dstWidth, jint dstHeight, jint offsetWidth, jint offsetHeight) {
Geometry.c (jni\filters):void JNIFUNCF(ImageFilterGeometry, nativeApplyFilterStraighten, jobject src, jint srcWidth, jint srcHeight, jobject dst, jint dstWidth, jint dstHeight, jfloat straightenAngle) {
Hue.c (jni\filters):void JNIFUNCF(ImageFilterHue, nativeApplyFilter, jobject bitmap, jint width, jint height, jfloatArray matrix)
ImageFilterBW.java (src\com\android\gallery3d\filtershow\filters):    native protected void nativeApplyFilter(Bitmap bitmap, int w, int h);
ImageFilterBW.java (src\com\android\gallery3d\filtershow\filters):        nativeApplyFilter(bitmap, w, h);

Native方法的实现，肯定是在C或CPP中，直接看第一个结果吧：

void JNIFUNCF(ImageFilterBW, nativeApplyFilter, jobject bitmap, jint width, jint height)
{
    ...
}

JNIFUNCF这个函数名有点怪啊，怎么全是大写，C或C++中，全大写一般是都常量或宏，啥情况？

看看是怎么定义的，再根据JNIFUNCF搜索下，在filters.h中有定义：

#define JNIFUNCF(cls, name, vars...) Java_com_android_gallery3d_filtershow_filters_ ## cls ## _ ## name(JNIEnv* env, jobject obj, vars)

原来是个宏，这个宏是啥意思如果你不明白，需要了解一些C的基础，

此处将 “Java_com_android_gallery3d_filtershow_filters_” 和 cls 对应的实际值和 name 对应的实际值，拼接成一个字符串作为实际的方法名。

之前我们修改了Java的包名，但是 Java_com_android_gallery3d_filtershow_filters_ 这个没有修改，所以导致最终生成的方法与修改后Java实现的Native方法的符号匹配不上了，将 Java_com_android_gallery3d_filtershow_filters_ 修改成 Java_com_zhao3546_gallery3d_filtershow_filters_ ，再放到源码编译环境上重新生成相应的so，再重新生成APK测试，ok，问题解决。

 

了解JNI机制，才是解决此类问题的KEY。