Sharedpreferences 保存后返回空值

Question

我有一个带有两个单选按钮的单选组。我想选择一个单选按钮并点击保存，这样当我返回时，同一个单选按钮就会被选中。问题是，即使在我点击保存 onCreate 中的 sharedpreferences 后，它也总是返回 null。我知道保存功能正在执行，因为 toast 运行并且我在控制台中打印了 System.out.println。

public void saveSettings(View view)
{
    Toast.makeText(getApplicationContext(), "Settings Saved", Toast.LENGTH_LONG).show();

    //DETERMINE WHICH RADIO BUTTON IS SELECTED
    RadioButton lbSetting = (RadioButton)findViewById(R.id.weightSettingLB);
    RadioButton kgSetting = (RadioButton)findViewById(R.id.weightSettingKG);
    if(lbSetting.isChecked())
    {
        weightSetting = "lb";
    }
    if(kgSetting.isChecked())
    {
        weightSetting = "kg";
    }

    System.out.println("The " + weightSetting + " radio button has been selected.");

    //SAVE WEIGHT SETTING BETWEEN LB/KG
    settingsPrefString = getSharedPreferences(weightSetting, 0);
    SharedPreferences.Editor editor = settingsPrefString.edit();
    editor.putString("weightSetting", weightSetting);
    editor.commit();
}

在我的 onCreate 中，我尝试将保存的数据检索为

if(settingsPrefString != null)
{
    weightSetting = settingsPrefString.getString("weightSetting", "Couldn't load data!");
}
if(settingsPrefString == null)
{
    System.out.println("settingsPrefString is NULL!");
}

即使在我点击保存后，sharedpreferences 也总是返回为 null。

Answer 1

在需要时调用这些函数：

private void savePreferences(String key, String value){
    SharedPreferences sharedPreferences = getSharedPreferences("weightSetting", MODE_PRIVATE);
    SharedPreferences.Editor editor = sharedPreferences.edit();
    editor.putString(key, value);
    editor.commit();
   }


  private String loadPreferences(String key){
    SharedPreferences sharedPreferences = getSharedPreferences("weightSetting", MODE_PRIVATE);
    String load = sharedPreferences.getString(key, "");
    return load;

   }
}

例如：

savePreferences("selected", "lb");

和

String s = loadPreferences("selected);

Answer 2

您正在做的错误是在 saveSettings 方法中。在为第一个创建共享首选项时，您没有为其分配常量名称，因为您已使用变量作为名称，因此请更改它。为相同创建一个全局字符串常量

//SAVE WEIGHT SETTING BETWEEN LB/KG
settingsPrefString = getSharedPreferences(weightSetting, 0);
SharedPreferences.Editor editor = settingsPrefString.edit();

到

public static final String SETTINGS_PREFERENCE = "SETTINGS_PREFERENCE"
SharedPreference settingsPrefString

//your code
//saveSettings method
//SAVE WEIGHT SETTING BETWEEN LB/KG
settingsPrefString = getSharedPreferences(SETTINGS_PREFERENCE , Context.MODE_PRIVATE);
SharedPreferences.Editor editor = settingsPrefString.edit();

如果您查看更改，则会使用两个常量，这使代码更具可读性和可访问性。

下次在你的 onCreate() 方法中你必须添加

settingsPrefString = getSharedPreferences(SETTINGS_PREFERENCE , Context.MODE_PRIVATE);

if(settingsPrefString != null)
{
    weightSetting = settingsPrefString.getString("weightSetting", "Couldn't load data!");
} else {
    System.out.println("settingsPrefString is NULL!");
}

Answer 3

替换

settingsPrefString = getSharedPreferences(weightSetting, 0);

有

settingsPrefString = getSharedPreferences(weightSetting, Context.MODE_PRIVATE);

这也有帮助

settingsPrefString = PreferenceManager.getDefaultSharedPreferences(this);

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