首先你得
#include <jni.h>

弄到全局Context
jobject getContext(JNIEnv *env,JavaVM *vm)
{
jclass activityThread = env->FindClass("android/app/ActivityThread");
jmethodID currentActivityThread = env->GetStaticMethodID(activityThread, "currentActivityThread", "()Landroid/app/ActivityThread;");
jobject at = env->CallStaticObjectMethod(activityThread, currentActivityThread);
jmethodID getApplication = env->GetMethodID(activityThread, "getApplication", "()Landroid/app/Application;");
jobject context = env->CallObjectMethod(at, getApplication);
return context;
}

Toast主代码
void toast(JNIEnv *env,JavaVM *vm,char* str,jint time)
{
jobject context = getContext(env,vm);
jclass tclss = env->FindClass("android/widget/Toast");
jmethodID mid = env->GetStaticMethodID(tclss,"makeText","(Landroid/content/Context;Ljava/lang/CharSequence;I)Landroid/widget/Toast;");
jobject job = env->CallStaticObjectMethod(tclss,mid,context,env->NewStringUTF(str),time);
jmethodID showId = env->GetMethodID(tclss,"show","()V");
env->CallVoidMethod(job,showId);
}

JavaVM通过JNI_OnLoad方法参数可得
JNIEnv可通过JavaVM指针->GetEnv((void **)&JNIEnv指针, JNI_VERSION_1_6)可得

完毕

首先你得打开一个项目

那么问题来了，内存溢出咋办