android利用JNI调用C++自定义类

拼搏现实的明天。 2022-07-15 03:14 216阅读 0赞

找了好久关于android调用C/C++库的文章，但是始终没有一片是关于android利用jni调用C++自定义类的文章，无奈只好看android的源代码，学习android的图形库的实现，因为它的实现底层也是利用C++的skia库。下面就3个文件来描述。

首先是你在[Java][]中的一个类，用于你在应用程序中调用这里取名叫Person类

**\[java\]** [view plain][] [copy][view plain]

1.  **package** whf.jnitest; 
2.  
3.  **public****class** Person \{ 
4.  
5.  **static**
6.   \{ 
7.   System.loadLibrary("Person"); 
8.   \} 
9.  
10. **private****int** mNativePerson; 
11. 
12. **public** Person() 
13.  \{ 
14.  mNativePerson = init(); 
15.  \} 
16. **protected****void** finalize() 
17.  \{ 
18. **try** \{ 
19. finalizer(mNativePerson); 
20.  \} **finally** \{ 
21. **try** \{ 
22. **super**.finalize(); 
23.  \} **catch** (Throwable e) \{ 
24. // TODO Auto-generated catch block
25.  e.printStackTrace(); 
26.  \} 
27.  \} 
28.  \} 
29. **public****int** getAge() 
30.  \{ 
31. **return** native\_getAge(mNativePerson); 
32.  \} 
33. 
34. **public****void** setAge(**int** age) 
35.  \{ 
36.  native\_setAge(mNativePerson, age); 
37.  \} 
38. 
39. **private****native****void**finalizer(**int** nPerson); 
40. **public****native****int** add(**int** a, **int** b); 
41. **public****native****int** sub(**int** a, **int** b); 
42. **private****native****int** init(); 
43. 
44. **private****native****int** native\_getAge(**int** nPerson); 
45. **private****native****void** native\_setAge(**int** nPerson, **int** age); 
46. \}

然后你的C++文件就如下，我定义为CPerson类

**\[cpp\]** [view plain][] [copy][view plain]

1.  \#define LOG\_TAG "this is a first JNI test"
2.  
3.  \#include <stdio.h>
4.  \#include <stdlib.h>
5.  \#include <unistd.h>
6.  \#include <sys/types.h>
7.  \#include <sys/stat.h>
8.  \#include <fcntl.h>
9.  \#include <assert.h>
10. \#include "jni.h"
11. \#include "CPerson.h"
12. 
13. 
14. 
15.  jint add(JNIEnv \*env, jobject obj, jint a, jint b) 
16.  \{ 
17. **return** a + b; 
18.  \} 
19. 
20.  jint Java\_whf\_jnitest\_Person\_sub(JNIEnv \*env, jobject obj, jint a, jint b) 
21.  \{ 
22. **return** a - b; 
23.  \} 
24. 
25. **void**Java\_whf\_jnitest\_Person\_finalizer(JNIEnv \*env, jobject clazz, CPerson \*obj) 
26.  \{ 
27. **delete** obj; 
28.  \} 
29. 
30.  CPerson \* Java\_whf\_jnitest\_Person\_init(JNIEnv \*env, jobject clazz) 
31.  \{ 
32.  CPerson \*p = **new** CPerson(); 
33. **return** p; 
34.  \} 
35. 
36. **void**Java\_whf\_jnitest\_Person\_setAge(JNIEnv \*env, jobject clazz, CPerson \*obj, jint age) 
37.  \{ 
38. **return** obj->setAge(age); 
39.  \} 
40. 
41.  jint Java\_whf\_jnitest\_Person\_getAge(JNIEnv \*env, jobject clazz, CPerson \*obj) 
42.  \{ 
43. **return** obj->getAge(); 
44.  \} 
45. 
46. **static** JNINativeMethod methods\[\]\{ 
47.  \{ "add", "(II)I", (**void** \*)add\}, 
48.  \{ "sub", "(II)I", (**void** \*)Java\_whf\_jnitest\_Person\_sub\}, 
49.  \{ "finalizer", "(I)V", (**void** \*)Java\_whf\_jnitest\_Person\_finalizer\}, 
50.  \{ "init", "()I", (**void** \*)Java\_whf\_jnitest\_Person\_init\}, 
51.  \{ "native\_setAge", "(II)V", (**void** \*)Java\_whf\_jnitest\_Person\_setAge\}, 
52.  \{ "native\_getAge", "(I)I", (**void** \*)Java\_whf\_jnitest\_Person\_getAge\}, 
53.  \}; 
54. 
55. **static****const****char** \* classPathName = "whf/jnitest/Person"; 
56. 
57. **static****int** registerNativeMethods(JNIEnv\* env, **const****char**\* className, 
58.  JNINativeMethod\* gMethods, **int** numMethods) 
59.  \{ 
60.  jclass clazz; 
61. 
62.  clazz = env->FindClass(className); 
63. **if** (clazz == NULL) \{ 
64. //LOGE("Native registration unable to find class '%s'", className);
65. **return** JNI\_FALSE; 
66.  \} 
67. **if** (env->RegisterNatives(clazz, gMethods, numMethods) < 0) \{ 
68. //LOGE("RegisterNatives failed for '%s'", className);
69. **return** JNI\_FALSE; 
70.  \} 
71. 
72. **return** JNI\_TRUE; 
73.  \} 
74. 
75. **static****int** registerNatives(JNIEnv\* env) 
76.  \{ 
77. **if** (!registerNativeMethods(env, classPathName, 
78.  methods, **sizeof**(methods) / **sizeof**(methods\[0\]))) \{ 
79. **return** JNI\_FALSE; 
80.  \} 
81. 
82. **return** JNI\_TRUE; 
83.  \} 
84. 
85. **typedef****union** \{ 
86.  JNIEnv\* env; 
87. **void**\* venv; 
88.  \} UnionJNIEnvToVoid; 
89. 
90. /\* This function will be call when the library first be loaded \*/
91.  jint JNI\_OnLoad(JavaVM\* vm, **void**\* reserved) 
92.  \{ 
93.  UnionJNIEnvToVoid uenv; 
94.  JNIEnv\* env = NULL; 
95. //LOGI("JNI\_OnLoad!");
96. 
97. **if** (vm->GetEnv((**void**\*\*)&uenv.venv, JNI\_VERSION\_1\_4) != JNI\_OK) \{ 
98. //LOGE("ERROR: GetEnv failed");
99. **return** \-1; 
100.  \} 
101. 
102.  env = uenv.env;; 
103. 
104. //jniRegisterNativeMethods(env, "whf/jnitest/Person", methods, sizeof(methods) / sizeof(methods\[0\]));
105. 
106. **if** (registerNatives(env) != JNI\_TRUE) \{ 
107. //LOGE("ERROR: registerNatives failed");
108. **return** \-1; 
109.  \} 
110. 
111. **return** JNI\_VERSION\_1\_4; 
112.  \}

CPerson的声明如下：

**\[cpp\]** [view plain][] [copy][view plain]

1.  \#ifndef \_CPERSON\_H\_
2.  \#define \_CPERSON\_H\_
3.  
4.  **class** CPerson 
5.  \{ 
6.  **private**: 
7.  **int** m\_age; 
8.  **public**: 
9.   CPerson(); 
10. **int** getAge(); 
11. **void** setAge(**int** age); 
12. \}; 
13. 
14. \#endif

这样一个简单的JNI调用C++自定义类就实现了

http://blog.csdn.net/wanghaofeng/article/details/7781094

[Java]: http://lib.csdn.net/base/javaee
[view plain]: http://blog.csdn.net/wanghaofeng/article/details/7781094#