第一行代码--Chapter6

2021-10-23

一、存储数据到文件

openFileOutput()：将数据存储到指定文件

public void save(String inputText) {
  FileOutputStream out = null;
  BufferedWriter writer = null;
  try {
    out = openFileOutput("data", Context.MODE_PRIVATE);
    writer = new BufferedWriter(new OutputStreamWriter(out));
    writer.write(inputText);
  } catch (IOException e) {
    e.printStackTrace();
  } finally {
    try {
      if (writer != null) {
        writer.close();
      }
    } catch (IOException e) {
      e.printStackTrace();
    }
  }
}

二、从文件读取数据

openFileInput()：从文件中读取数据

public String load() {
  FileInputStream in = null;
  BufferedReader reader = null;
  StringBuilder content = new StringBuilder();
  try {
    in = openFileInput("data");
    reader = new BufferedReader(new InputStreamReader(in));
    String line = "";
    while ((line = reader.readLine()) != null) {
      content.append(line);
    }
  } catch (IOException e) {
    e.printStackTrace();
  } finally {
    if (reader != null) {
      try {
        reader.close();
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
  }
  return content.toString();
}

EditText.setSelection()：将输入光标移动到文本末尾

TextUtils.isEmpty()：当传入字符串等于null或者空字符串时返回true

三、SharedPrefenrences存储和读取

使用键值对存储数据，若存储数据为整型，则读取出来的也是整型；若存储数据为字符串，则读取出来的也是字符串。

存储步骤：

Step1：调用SharedPreferences对象的edit()方法来获取一个ShredPreferences.Editor对象

Step2：想SharedPreferences.Editor对象添加数据

Step3：调用apply方法提交数据

SharedPreferences.Editor editor = getSharedPreferences("data",MODE_MULTI_PROCESS).edit();
editor.putString("name","Tom");
editor.putInt("age",28);
editor.putBoolean("married",false);
editor.apply();

读取数据：

SharedPreferences pref = getSharedPreferences("data", MODE_PRIVATE);
String name = pref.getString("name", "");
int age = pref.getInt("age", 0);
boolean married = pref.getBoolean("married", false);
Log.d("MainActivity", "name is " + name);
Log.d("MainActivity", "age is " + age);
Log.d("MainActivity", "married is " + married);