//获取当前设备可用内存（单位：MB）

-(double)availableMemory{

    vm_statistics_data_t vmStats;

    mach_msg_type_number_t infoCount = HOST_VM_INFO_COUNT;

    kern_return_t kernReturn = host_statistics(mach_host_self(), HOST_VM_INFO, (host_info_t)&vmStats, &infoCount);

    if (kernReturn != KERN_SUCCESS) {

        return NSNotFound;

    }

    return ((vm_page_size * vmStats.free_count) / 1024.0)/1024.0;

}

//获取当前任务所占的内存，单位：MB

-(double)usedMemory{

    task_basic_info_data_t taskInfo;

    mach_msg_type_number_t infoCount;

    kern_return_t kernReturn = task_info(mach_task_self(), TASK_BASIC_INFO, (task_info_t)&taskInfo, &infoCount);

    if (kernReturn != KERN_SUCCESS) {

        return NSNotFound;

    }

    return (taskInfo.resident_size / 1024.0 / 1024.0);

}