Android JNI-来自C ++的Android UI线程上的调用函数

正如@Elviss提到的-
将代码发布到主线程中，您应该使用

Looper

java.lang.Runnable

Android
NDK提供了极其轻便高效的方式来将本机代码发布到任意循环程序。关键是您应该向循环程序提供任意文件描述符，并指定您感兴趣的文件事件（输入，输出等）。在后台，looper会轮询该文件描述符，一旦事件可用，它将在适当的线程上运行您的回调。

有一个最小的示例（没有错误检查和删除）：

#include <android/looper.h>#include <unistd.h>#define LOGI(...) __android_log_print(ANDROID_LOG_INFO, "sergik", __VA_ARGS__)static ALooper* mainThreadLooper;static int messagePipe[2];static int looperCallback(int fd, int events, void* data);void someJniFuncThatYouShouldCallonceOnMainThread() {    mainThreadLooper = ALooper_forThread(); // get looper for this thread    ALooper_acquire(mainThreadLooper); // add reference to keep object alive    pipe(messagePipe); //create send-receive pipe    // listen for pipe read end, if there is something to read    // - notify via provided callback on main thread    ALooper_addFd(mainThreadLooper, messagePipe[0],       0, ALOOPER_EVENT_INPUT, looperCallback, nullptr);    LOGI("fd is registered");    // send few messages from arbitrary thread    std::thread worker([]() {        for(char msg = 100; msg < 110; msg++) { LOGI("send message #%d", msg); write(messagePipe[1], &msg, 1); sleep(1);        }    });    worker.detach();}// this will be called on main threadstatic int looperCallback(int fd, int events, void* data) {    char msg;    read(fd, &msg, 1); // read message from pipe    LOGI("got message #%d", msg);    return 1; // continue listening for events}

此代码产生下一个输出：

06-28 23:28:27.076 30930-30930/? I/sergik: fd is registered06-28 23:28:27.076 30930-30945/? I/sergik: send message #10006-28 23:28:27.089 30930-30930/? I/sergik: got message #10006-28 23:28:28.077 30930-30945/? I/sergik: send message #10106-28 23:28:28.077 30930-30930/? I/sergik: got message #10106-28 23:28:29.077 30930-30945/? I/sergik: send message #10206-28 23:28:29.078 30930-30930/? I/sergik: got message #10206-28 23:28:30.078 30930-30945/? I/sergik: send message #10306-28 23:28:30.078 30930-30930/? I/sergik: got message #10306-28 23:28:31.079 30930-30945/? I/sergik: send message #10406-28 23:28:31.079 30930-30930/? I/sergik: got message #10406-28 23:28:32.079 30930-30945/? I/sergik: send message #10506-28 23:28:32.080 30930-30930/? I/sergik: got message #10506-28 23:28:33.080 30930-30945/? I/sergik: send message #10606-28 23:28:33.080 30930-30930/? I/sergik: got message #10606-28 23:28:34.081 30930-30945/? I/sergik: send message #10706-28 23:28:34.081 30930-30930/? I/sergik: got message #10706-28 23:28:35.081 30930-30945/? I/sergik: send message #10806-28 23:28:35.082 30930-30930/? I/sergik: got message #10806-28 23:28:36.082 30930-30945/? I/sergik: send message #10906-28 23:28:36.083 30930-30930/? I/sergik: got message #109

从pid-tid对中可以看到-消息是在主线程上接收的。当然，您可能会发送比一字节消息更复杂的内容。