Data storage

In some application scenarios, it is necessary to permanently store some information (save data after power-off), such as account numbers, passwords or other configuration information. The characteristics of these data are: the total amount is small, but it needs flexible access. In such cases, there is no need to use a database. We provide a set of simple data storage interfaces, which are stored in the form of key-value pairs.

• Required header files

    #include "storage/StoragePreferences.h"
  

• Main interface

    // Storage interface
    static bool putString(const std::string &key, const std::string &val);
    static bool putInt(const std::string &key, int val);
    static bool putBool(const std::string &key, bool val);
    static bool putFloat(const std::string &key, float val);
  
    // delete the specified key
    static bool remove(const std::string &key);
    // Clear storage data
    static bool clear();
  
    // Get the interface, if the corresponding key value is not obtained, return the default value of defVal
    static std::string getString(const std::string &key, const std::string &defVal);
    static int getInt(const std::string &key, int defVal);
    static bool getBool(const std::string &key, bool defVal);
    static float getFloat(const std::string &key, float defVal);
  

[!Warning]

1. This interface saves the data in the flash as a file, so do not write frequently to cause damage to the flash.
2. The size of the partition is limited. The size of the partition varies depending on the model of the screen. Try to keep the data size within 512KB.

Usage example

• Save

  //Save the string, use "username" as the alias, and the value is the name string
  const char* name = "zhang san";
  StoragePreferences::putString("username", name);
  

  //Save the boolean variable, use "power" as the alias, the value is true
  StoragePreferences::putBool("power", true);
  

  //Save the floating point number, using "temperature" as the alias, the value is 30.12
  StoragePreferences::putFloat("temperature", 30.12);
  

  //Save the integer, use "age" as the alias, the value is 20
  StoragePreferences::putInt("age", 20);
  

• Read

  //Read the value of the "username" key, if there is no value, return an empty string
  std::string name = StoragePreferences::getString("username", "");
  //Log print the string read
  LOGD("username %s\n", username.c_str());
  

  //Read Boolean variable, if there is no value, then specify to return false
  bool power = StoragePreferences::getBool("power", false);
  

  //Read floating point number, if there is no value, specify to return 0
  float temperature = StoragePreferences::getFloat("temperature", 0);
  

  //Read the integer, if there is no value, return 18
  int age = StoragePreferences::getInt("age", 18);
  

• Delete

  //Clear a value individually
  StoragePreferences::remove("username");
  StoragePreferences::remove("power");
  StoragePreferences::remove("temperature");
  StoragePreferences::remove("age");
  //Clear all values
  StoragePreferences::clear();
  

• Modify If you need to modify a value, just save the key value repeatedly, and the old value will be automatically overwritten