如何将此 class 设为单例？

Question

我正在尝试将此 class 设为单例，但没有成功。你会怎么做？我在互联网上看到我应该对头文件和 cpp 文件进行修改。我只尝试通过更改 cpp 文件... 我需要做的是能够从 JNI 调用中访问布尔值“isRecording”。

谢谢。

OboeAudioRecorder.cpp

#include <jni.h>
#include <string>
#include <oboe/Oboe.h>
#include "OboeAudioRecorder.h"
#include "oboe/samples/debug-utils/logging_macros.h"

class OboeAudioRecorder: public oboe::AudioStreamCallback {
public:
    bool isRecording = true;

    explicit OboeAudioRecorder() { }

    void StartAudioRecorder() {
        oboe::AudioStreamBuilder builder;
        builder.setDirection(oboe::Direction::Input);
        builder.setPerformanceMode(oboe::PerformanceMode::LowLatency);
        builder.setFormat(oboe::AudioFormat::Float);
        builder.setChannelCount(oboe::ChannelCount::Mono);
        builder.setInputPreset(oboe::InputPreset::Unprocessed);
        builder.setSharingMode(oboe::SharingMode::Shared);
        builder.setSampleRate(48000);
        builder.setAudioApi(oboe::AudioApi::OpenSLES);
        //builder.setCallback(this);

        oboe::Result r = builder.openStream(&stream);
        if (r != oboe::Result::OK) {
            return;
        }

        r = stream->requestStart();
        if (r != oboe::Result::OK) {
            return;
        }

        auto a = stream->getState();
        if (a == oboe::StreamState::Started) {

            constexpr int kMillisecondsToRecord = 2;
            const int32_t requestedFrames = (int32_t) (kMillisecondsToRecord * (stream->getSampleRate() / oboe::kMillisPerSecond));
            __android_log_print(ANDROID_LOG_INFO, "OboeAudioRecorder", "requestedFrames = %d", requestedFrames);
            float_t mybuffer[requestedFrames];
            constexpr int64_t kTimeoutValue = 3 * oboe::kNanosPerMillisecond;

            int framesRead = 0;
            do {
                auto result = stream->read(mybuffer, requestedFrames, 0);
                if (result != oboe::Result::OK) {
                    break;
                }
                framesRead = result.value();
                __android_log_print(ANDROID_LOG_INFO, "OboeAudioRecorder", "framesRead = %d", framesRead);
                if (framesRead > 0) {
                    break;
                }
            } while (framesRead != 0);

            while (isRecording) {
                auto result = stream->read(mybuffer, requestedFrames, kTimeoutValue * 1000);
                if (result == oboe::Result::OK) {
                    auto nbFramesRead = result.value();
                    __android_log_print(ANDROID_LOG_INFO, "OboeAudioRecorder", "nbFramesRead = %d", nbFramesRead);
                    for (int i=0; i<nbFramesRead; i++) {
                        __android_log_print(ANDROID_LOG_INFO, "OboeAudioRecorder", "nbFramesRead[%d] = %f", i, mybuffer[i]);
                    }
                } else {
                    auto error = convertToText(result.error());
                    __android_log_print(ANDROID_LOG_INFO, "OboeAudioRecorder", "error = %s", error);
                }
            }

            stream->requestStop();
            stream->close();
        }
    }

    oboe::DataCallbackResult onAudioReady(oboe::AudioStream *oboeStream, void *audioData, int32_t numFrames) override {
        LOGE("onAudioReady");
    }

private:
    oboe::ManagedStream outStream;
    oboe::AudioStream *stream{};
};

OboeAudioRecorder.h

#ifndef OBOEAUDIORECORDER_OBOEAUDIORECORDER_H
#define OBOEAUDIORECORDER_OBOEAUDIORECORDER_H


#endif //OBOEAUDIORECORDER_OBOEAUDIORECORDER_H

Answer 1

由于以下 link（法语），我能够将此 class 设为单例：https://h-deb.clg.qc.ca/Sujets/Divers--cplusplus/CPP--Singletons.html

这是我的 class 单例模式（注意声明在“class”范围之外的最后一行）：

#include <jni.h>
#include <string>
#include <oboe/Oboe.h>
#include "OboeAudioRecorder.h"
#include "oboe/samples/debug-utils/logging_macros.h"

class OboeAudioRecorder: public oboe::AudioStreamCallback {

private:
    oboe::ManagedStream outStream;
    oboe::AudioStream *stream{};

    oboe::DataCallbackResult
    onAudioReady(oboe::AudioStream *oboeStream, void *audioData, int32_t numFrames) override {
        LOGE("onAudioReady");
    }

    static OboeAudioRecorder *singleton;
    explicit OboeAudioRecorder() = default;

public:
    static OboeAudioRecorder *get() {
        if (!singleton)
            singleton = new OboeAudioRecorder();
        return singleton;
    }

    bool isRecording = true;

    void StartAudioRecorder() {
        oboe::AudioStreamBuilder builder;
        builder.setDirection(oboe::Direction::Input);
        builder.setPerformanceMode(oboe::PerformanceMode::LowLatency);
        //builder.setFormat(oboe::AudioFormat::Float);
        builder.setFormat(oboe::AudioFormat::I16);
        builder.setChannelCount(oboe::ChannelCount::Mono);
        builder.setInputPreset(oboe::InputPreset::Unprocessed);
        builder.setSharingMode(oboe::SharingMode::Shared);
        builder.setSampleRate(48000);
        builder.setAudioApi(oboe::AudioApi::OpenSLES);
        //builder.setCallback(this);

        oboe::Result r = builder.openStream(&stream);
        if (r != oboe::Result::OK) {
            return;
        }

        r = stream->requestStart();
        if (r != oboe::Result::OK) {
            return;
        }

        auto a = stream->getState();
        if (a == oboe::StreamState::Started) {

            constexpr int kMillisecondsToRecord = 2;
            auto requestedFrames = (int32_t) (kMillisecondsToRecord *
                                                       (stream->getSampleRate() /
                                                        oboe::kMillisPerSecond));
            __android_log_print(ANDROID_LOG_INFO, "OboeAudioRecorder", "requestedFrames = %d",
                                requestedFrames);
            //const int32_t requestedFrames = 65536;
            //int16_t mybuffer[requestedFrames];
            int16_t mybuffer[requestedFrames];
            constexpr int64_t kTimeoutValue = 3 * oboe::kNanosPerMillisecond;

            int framesRead = 0;
            do {
                auto result = stream->read(mybuffer, requestedFrames, 0);
                if (result != oboe::Result::OK) {
                    break;
                }
                framesRead = result.value();
                __android_log_print(ANDROID_LOG_INFO, "OboeAudioRecorder", "framesRead = %d",
                                    framesRead);
                if (framesRead > 0) {
                    break;
                }
            } while (framesRead != 0);

            while (isRecording) {
                auto result = stream->read(mybuffer, requestedFrames, kTimeoutValue * 1000);
                if (result == oboe::Result::OK) {
                    auto nbFramesRead = result.value();
                    __android_log_print(ANDROID_LOG_INFO, "OboeAudioRecorder", "nbFramesRead = %d",
                                        nbFramesRead);
                    for (int i = 0; i < nbFramesRead; i++) {
                        __android_log_print(ANDROID_LOG_INFO, "OboeAudioRecorder",
                                            "nbFramesRead[%d] = %d", i, mybuffer[i]);
                    }
                } else {
                    auto error = convertToText(result.error());
                    __android_log_print(ANDROID_LOG_INFO, "OboeAudioRecorder", "error = %s", error);
                }
            }

            stream->requestStop();
            stream->close();
        }
    }


};

OboeAudioRecorder *OboeAudioRecorder::singleton = nullptr;

Answer 2

使 class 成为单例的一种简单方法是添加一个在方法中使用静态变量的 getInstance() 方法。

static OboeAudioRecorder &getInstance() {
    static EngineOpenSLES sInstance;
    return sInstance;
}

您还可以通过将构造函数设为私有并删除复制运算符来防止创建其他实例：

private:
    // Make this a safe Singleton
    OboeAudioRecorder()= default;
    ~OboeAudioRecorder()= default;
public:
    OboeAudioRecorder(const OboeAudioRecorder&)= delete;
    OboeAudioRecorder& operator=(const OboeAudioRecorder&)= delete;

如何将此 class 设为单例？

How would to make this class as a singleton?

android

android-ndk

java-native-interface

singleton

oboe