Android JNI sample code

In this article, we will introduce how to use Android JNI through several steps, hoping to help you.

You can modify the Android mobile phone operating system in the android modulo simulator to add various functions to meet your needs. So today we will bring you the android JNI-related usage methods to facilitate your interpretation of this system. In Android applications (Dalvik VM), JNI (Java Native Interface) is used to call the shared libraries developed by C/C ++.

• Overview of various functions of the android Java package
• Tips for using the android call Platform
• Overview of the basic content of the android program architecture
• How Android judges the network status
• Android unit test source code

Development Environment

1. (Eclipse + Android ADT)
2. Windows XP SP3
3. JDK 1.6.0.12
4. VMware + Ubuntu Linux 8.04

Steps for using Android JNI (1) Create an android project in eclipse

1. Project name: jnitest
2. Package name com. Ura. Test
3. Activity name jnitest
4. Application name: jnitest

Steps for using Android JNI (2) EDIT main. xml

1. <? XML version = "1.0" encoding = "UTF-8"?>
2. <Linearlayout xmlns: Android =
   Http://schemas.Android.com/apk/res/Android"
3. Android: Orientation = "vertical"
4. Android: layout_width = "fill_parent"
5. Android: layout_height = "fill_parent"
6. >
7. <Textview
8. Android: Id = "@ + ID/jnitest"
9. Android: layout_width = "fill_parent"
10. Android: layout_height = "wrap_content"
11. Android: text = "@ string/jnitest"
12. />
13. </Linearlayout>

Steps for using Android JNI (3) edit a Java File

1. Package com. Ura. test;
2. Import Android. App. activity;
3. Import Android. OS. Bundle;
4. Import Android. widget. textview;
5. Public class jnitest extends activity {
6. /** Called when the activity is first created .*/
7. Static {
8. System. loadlibrary ("jnitest ");
9. }
10. Public native string gettest ();
11. @ Override
12. Public void oncreate (bundle savedinstancestate ){
13. Super. oncreate (savedinstancestate );
14. Setcontentview (R. layout. Main );
15. String STR = gettest ();
16. Textview jnitest = (textview) findviewbyid (R. Id. jnitest );
17. Jnitest. settext (STR );
18. }
19. }

Steps for using Android JNI (4) to generate a head File　

Compile the above project and claim the class file, and then use javah to generate the C/C ++ header file.

1. Javah-classpath bin-d jni com. Ura. Test. jnitest

The generated header file is as follows:

1. /* Do not edit this file-it is machine generated */
2. # Include <JNI. h>
3. /* Header for class com_ura_test_jnitest */
4. # Ifndef _ included_com_ura_test_jnitest
5. # DEFINE _ included_com_ura_test_jnitest
6. # Ifdef _ cplusplus
7. Extern "C "{
8. # Endif
9. /*
10. * Class: com_ura_test_jnitest
11. * Method: gettest
12. * Signature: () ljava/lang/string;
13. */
14. Jniexport jstring jnicall java_com_ura_test_jnitest_gettest
15. (Jnienv *, jobject );
16. # Ifdef _ cplusplus
17. }
18. # Endif
19. # Endif

Step 5: Compile the C/C ++ file as follows:

1. # Include "com_ura_test_jnitest.h"
2. # Define log_tag "jnitest"
3. # UNDEF log
4. # Include <utils/log. h>
5. Jniexport jstring jnicall java_com_ura_test_jnitest_gettest
6. (Jnienv * ENV, jobject OBJ)
7. {
8. Return (* env)-> newstringutf (ENV, (char *)
   "Jnitest native string ");
9. Logd ("Hello Lib! \ N ");
10. }

Step 6: Compile the Android. mk File

1. Local_path: = $ (call my-DIR)
2. Include $ (clear_vars)
3. Local_src_files: = \
4. Com_ura_test_jnitest.c
5. Local_c_includes: = \
6. $ (Jni_h_include)
7. Local_shared_libraries: = libutils
8. Local_prelink_module: = false
9. Local_module: = libjnitest
10. Include $ (build_shared_library)

Step 7: compile and generate a dynamic library for Android JNI

Create folder

1. ~ /Mydroid/external/libjnitest

Copy the header file, C/C ++ source file, and make file to the preceding directory.

* Set prelink_moudule to false.

Otherwise, you need to re-create an imgfile and then burn it in.

Run

1. CD
2. CD mydroid/build/
3. Envsetup. Sh
4. Cd ~ /Mydroid
5. CD external/libjnitest/
6. Mm

After compilation is successful, the libjnitest. So file will be generated in the following directory.

1. ~ Mydroid/out/target/product/generic/system/lib/

Steps for using Android JNI (8) execute a program in the simulator

First, copy the dynamic library to/system/lib.

Start the simulator

1. ADB Shell
2. ADB remount
3. ADB push libjnitest. So/system/lib

Confirm that the copy is successful.

1. CD/system/lib
2. Ls

Then do not close the simulator (turn it off and enable the dynamic library, because the simulator Rom is read-only)

Execute Java program jnitest

The screen is displayed.

Jnitest native string

The specific usage of Android JNI is described here.

[Responsible editor: Cao Kai Tel :( 010) 68476606]

 

Original article: Android JNI sample code

Tag: Android JNI