本文共 3790 字，大约阅读时间需要 12 分钟。

前言

chromium工程中，base::Value是一个数据的容器, 可以装double, string类型数据，数据的存取为key-value。

实验

找了一段现有的chromium代码，入参有base::Value, 尝试读取base::Value入参的内容。

Z:\chromium\src\chrome\browser\ui\webui\download_internals\download_internals_ui_message_handler.cc

bool DownloadInternalsUIMessageHandler::get_double_value_by_key_from_value(const base::Value& value, const char* psz_key, double& f_value){	bool b_rc = false;	const base::Value* p_bv_find_key = NULL;	do {		f_value = 0.0f;		if (NULL == psz_key) {			break;		}		p_bv_find_key = value.FindKey(psz_key);		if (NULL == p_bv_find_key) {			break;		}		if (!p_bv_find_key->is_double()) {			break;		}		f_value = p_bv_find_key->GetDouble();		b_rc = true;	} while (0);	return b_rc;}bool DownloadInternalsUIMessageHandler::get_string_value_by_key_from_value(const base::Value& value, const char* psz_key, std::string& str_value){	bool b_rc = false;	const base::Value* p_bv_find_key = NULL;	do {		str_value = "";		if (NULL == psz_key) {			break;		}		p_bv_find_key = value.FindKey(psz_key);		if (NULL == p_bv_find_key) {			break;		}		if (!p_bv_find_key->is_string()) {			break;		}		str_value = p_bv_find_key->GetString();		b_rc = true;	} while (0);	return b_rc;}void DownloadInternalsUIMessageHandler::OnServiceDownloadChanged(    const base::Value& service_download) {	double f_bytes_downloaded = 0.0f;	std::string str_client = "";	std::string str_state = "";	std::string str_file_path = "";	std::string str_guid = "";	std::string str_url = "";  if (!IsJavascriptAllowed())    return;  FireWebUIListener("service-download-changed", service_download);	/*+		[0]	("bytes_downloaded", unique_ptr DOUBLE 0.00000000000000000)	std::pair
   
    
     
      ,std::allocator
      
        >,std::unique_ptr
       
        
          > >+ [1] ("client", unique_ptr STRING "Debugging") std::pair
         
          
           
            ,std::allocator
            
              >,std::unique_ptr
             
              
                > >+ [2] ("file_path", unique_ptr STRING "C:\\Users\\LostSpeed\\AppData\\Local\\Chromium\\User Data\\Default\\Download Service\\Files\\205d0b7a-b28e-4594-943c-ec8e5180eda6") std::pair
               
                
                 
                  ,std::allocator
                  
                    >,std::unique_ptr
                   
                    
                      > >+ [3] ("guid", unique_ptr STRING "205d0b7a-b28e-4594-943c-ec8e5180eda6") std::pair
                     
                      
                       
                        ,std::allocator
                        
                          >,std::unique_ptr
                         
                          
                            > >+ [4] ("state", unique_ptr STRING "ACTIVE") std::pair
                           
                            
                             
                              ,std::allocator
                              
                                >,std::unique_ptr
                               
                                
                                  > >+ [5] ("url", unique_ptr STRING "https://download.csdn.net/download/lostspeed/10834374") std::pair
                                 
                                  
                                   
                                    ,std::allocator
                                    
                                      >,std::unique_ptr
                                     
                                      
                                        > > */ do { if (!get_double_value_by_key_from_value(service_download, "bytes_downloaded", f_bytes_downloaded)) { break; } if (!get_string_value_by_key_from_value(service_download, "client", str_client)) { break; } if (!get_string_value_by_key_from_value(service_download, "file_path", str_file_path)) { break; } if (!get_string_value_by_key_from_value(service_download, "guid", str_guid)) { break; } if (!get_string_value_by_key_from_value(service_download, "state", str_state)) { break; } if (!get_string_value_by_key_from_value(service_download, "url", str_url)) { break; } // COMPLETE DLOG(INFO) << "service_download info :" << "bytes_downloaded = " << f_bytes_downloaded << ", client = " << str_client << ", file_path = " << str_file_path << ", guid = " << str_guid << ", down_state = " << str_state << ", url = " << str_url; } while (0);}
                                      
                                     
                                    
                                   
                                  
                                 
                                
                               
                              
                             
                            
                           
                          
                         
                        
                       
                      
                     
                    
                   
                  
                 
                
               
              
             
            
           
          
         
        
       
      
     
    
   

记录的日志效果

[223200:240192:1218/130225.050:INFO:download_internals_ui_message_handler.cc(172)] service_download info :bytes_downloaded = 0, client = Debugging, file_path = C:\Users\LostSpeed\AppData\Local\Chromium\User Data\Default\Download Service\Files\b345452c-992c-47db-83ad-43606b7632ac, guid = b345452c-992c-47db-83ad-43606b7632ac, down_state = ACTIVE, url = https://download.csdn.net/download/lostspeed/10834374

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