Android NDK入门、提高和实战

核心提示：//步骤3jfloat ax = (*env)->GetFloatField(env, a, field_x);jfloat ay = (*env)->GetFloatField(env, a, field_y);jfloat bx = (*env)->GetFloatField(env, b, fi

//步骤3

jfloat ax = (*env)->GetFloatField(env, a, field_x);

jfloat ay = (*env)->GetFloatField(env, a, field_y);

jfloat bx = (*env)->GetFloatField(env, b, field_x);

jfloat by = (*env)->GetFloatField(env, b, field_y);

//步骤4

return sqrtf(powf(bx-ax, 2) + powf(by-ay, 2));

}

#include

#include

#include

jfloat Java_chroya_demo_ndk_Main_distance(JNIEnv* env, jobject thiz, jobject a,jobject b)

{

//步骤1

jclass point_class = (*env)->FindClass(env, "chroya/demo/ndk/Point");

if(point_class == NULL) {

//printf("class not found");

__android_log_write(ANDROID_LOG_INFO, "MyNdkDemo", "class Point not found");

return 0;

} else {

__android_log_write(ANDROID_LOG_INFO, "MyNdkDemo", "found class Point");

}

//步骤2

jfieldID field_x = (*env)->GetFieldID(env, point_class, "x", "F");

jfieldID field_y = (*env)->GetFieldID(env, point_class, "y", "F");

//步骤3

jfloat ax = (*env)->GetFloatField(env, a, field_x);

jfloat ay = (*env)->GetFloatField(env, a, field_y);

jfloat bx = (*env)->GetFloatField(env, b, field_x);

jfloat by = (*env)->GetFloatField(env, b, field_y);

//步骤4

return sqrtf(powf(bx-ax, 2) + powf(by-ay, 2));

}

然后在Java里面调用：

Java代码

public class Main extends Activity {

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

TextView tv = new TextView(getApplicationContext());

Point a = new Point();

a.x = 3;

a.y = 3;

Point b = new Point();