18 | 怎么减少 App 电量消耗？

在iOS中，IOKit framework 是专门用于跟硬件或内核服务通信的。所以，我们可以通过IOKit framework 来获取硬件信息，进而获取到电量消耗信息。在使用IOKit framework时，你需要：
首先，把IOPowerSources.h、IOPSKeys.h和IOKit 这三个文件导入到工程中；
然后，把batteryMonitoringEnabled置为true；
最后，通过如下代码获取1%精确度的电量信息。

#import "IOPSKeys.h"
#import "IOPowerSources.h"

-(double) getBatteryLevel{
    // 返回电量信息
    CFTypeRef blob = IOPSCopyPowerSourcesInfo();
    // 返回电量句柄列表数据
    CFArrayRef sources = IOPSCopyPowerSourcesList(blob);
    CFDictionaryRef pSource = NULL;
    const void *psValue;
    // 返回数组大小
    int numOfSources = CFArrayGetCount(sources);
    // 计算大小出错处理
    if (numOfSources == 0) {
        NSLog(@"Error in CFArrayGetCount");
        return -1.0f;
    }

    // 计算所剩电量
    for (int i=0; i<numOfSources; i++) {
        // 返回电源可读信息的字典
        pSource = IOPSGetPowerSourceDescription(blob, CFArrayGetValueAtIndex(sources, i));
        if (!pSource) {
            NSLog(@"Error in IOPSGetPowerSourceDescription");
            return -1.0f;
        }
        psValue = (CFStringRef) CFDictionaryGetValue(pSource, CFSTR(kIOPSNameKey));

        int curCapacity = 0;
        int maxCapacity = 0;
        double percentage;

        psValue = CFDictionaryGetValue(pSource, CFSTR(kIOPSCurrentCapacityKey));
        CFNumberGetValue((CFNumberRef)psValue, kCFNumberSInt32Type, &curCapacity);

        psValue = CFDictionaryGetValue(pSource, CFSTR(kIOPSMaxCapacityKey));
        CFNumberGetValue((CFNumberRef)psValue, kCFNumberSInt32Type, &maxCapacity);

        percentage = ((double) curCapacity / (double) maxCapacity * 100.0f);
        NSLog(@"curCapacity : %d / maxCapacity: %d , percentage: %.1f ", curCapacity, maxCapacity, percentage);
        return percentage;
    }
    return -1.

// 轮询检查多个线程 CPU 情况
+ (void)updateCPU {
    thread_act_array_t threads;
    mach_msg_type_number_t threadCount = 0;
    const task_t thisTask = mach_task_self();
    kern_return_t kr = task_threads(thisTask, &threads, &threadCount);
    if (kr != KERN_SUCCESS) {
        return;
    }
    for (int i = 0; i < threadCount; i++) {
        thread_info_data_t threadInfo;
        thread_basic_info_t threadBaseInfo;
        mach_msg_type_number_t threadInfoCount = THREAD_INFO_MAX;
        if (thread_info((thread_act_t)threads[i], THREAD_BASIC_INFO, (thread_info_t)threadInfo, &threadInfoCount) == KERN_SUCCESS) {
            threadBaseInfo = (thread_basic_info_t)threadInfo;
            if (!(threadBaseInfo->flags & TH_FLAGS_IDLE)) {
                integer_t cpuUsage = threadBaseInfo->cpu_usage / 10;
                if (cpuUsage > 90) {
                    //cup 消耗大于 90 时打印和记录堆栈
                    NSString *reStr = smStackOfThread(threads[i]);
                    //记录数据库中
                    [[[SMLagDB shareInstance] increaseWithStackString:reStr] subscribeNext:^(id x) {}];
                    NSLog(@"CPU useage overload thread stack：\n%@",reStr);
                }
            }
        }
    }
}