如何使SharedPreferences更新数据，而不是覆盖数据并丢失部分数据? [英] How can I make SharedPreferences to update the data instead of overwriting the data and losing part of it?

问题描述

我正在使用以下代码将ArrayList<String>保存到SharedPreferences中:

StringBuilder stringBuilder = new StringBuilder();

    for(String str: semesterArray) {
        stringBuilder.append(str);
        stringBuilder.append(",");
    }

    SharedPreferences sharedPreferences = getSharedPreferences("PREFERENCES", MODE_PRIVATE);
    SharedPreferences.Editor editor = sharedPreferences.edit();
    editor.putString("semesterArray", stringBuilder.toString());
    editor.apply();

这有点可以完成工作，因为它按预期方式保存了ArrayList<String>，并且当应用重新启动时，添加的Semesters仍按我希望的方式存储在ArrayList<String>中.但是，如果在重新启动应用程序后添加更多Semesters，则保存的Semesters将被覆盖，并且我将丢失之前保存的Semesters.有没有一种方法可以更新SharedPreferences而不是将其覆盖?如果不是，我应该朝哪个方向存储这些Semesters?感谢您的帮助！

解决方案

正如我在评论中提到的，使用sharedPrefences更新或插入新值不是一个好习惯，但是如果您要使用sharedPrefences，我会给您一个解决方案

您可以做的是:

1. 创建称为当前"的首选项以保存字符串的值
2. 创建另一个名为new的首选项，以在之后保存新数据 检查它是否不等于当前值.

您将以以下代码结尾:

 sharedPreferences = getSharedPreferences("shared",MODE_PRIVATE);
        editor = sharedPreferences.edit();
        String text = "first text";
        editor.putString("current",text);
        if (!sharedPreferences.getString("current","").equals(sharedPreferences.getString("new","")))
        {
            editor.putString("new",sharedPreferences.getString("current","") + text );
            editor.commit();

        }
        editor.commit();

首次保存后的结果:sharedPreferences.getString("current"，") 将返回某些文本"和sharedPreferences.getString("new"，")将 返回"

更改第一个文本"后的结果新文本" : sharedPreferences.getString("current"，")将返回"new text".和 sharedPreferences.getString("new"，")将返回第一个新的文本" 文字"

如何使用它:

  if sharedPreferences.getString("new","") equals ""
your data is not updated  use sharedPreferences.getString("current","")  
else  your data is updated so use sharedPreferences.getString("new","")

I'm using the following piece of code to save an ArrayList<String> into SharedPreferences:

StringBuilder stringBuilder = new StringBuilder();

    for(String str: semesterArray) {
        stringBuilder.append(str);
        stringBuilder.append(",");
    }

    SharedPreferences sharedPreferences = getSharedPreferences("PREFERENCES", MODE_PRIVATE);
    SharedPreferences.Editor editor = sharedPreferences.edit();
    editor.putString("semesterArray", stringBuilder.toString());
    editor.apply();

This is somewhat getting the job done since it saves the ArrayList<String> as intended and when the app is re-launched the Semesters that were added are still stored in the ArrayList<String> as I want them to be. But if I add more Semesters after re-launching the app, the Semesters that were saved are overwritten and I lose the previously saved Semesters. Is there a way SharedPreferences can be updated instead of overwritten? If not, in what direction should I move to store these Semesters? Thanks for the help!

解决方案

As i mentioned in my comment using sharedPrefences to update or insert new values is not a good practice , but i will give you a solution if you want to use sharedPrefences

what you can do is :

1. create prefrence called current to save the value of your string
2. create another prefrence called new , to save the new data after checking that it's not equal to the current.

you will end with something like this code :

 sharedPreferences = getSharedPreferences("shared",MODE_PRIVATE);
        editor = sharedPreferences.edit();
        String text = "first text";
        editor.putString("current",text);
        if (!sharedPreferences.getString("current","").equals(sharedPreferences.getString("new","")))
        {
            editor.putString("new",sharedPreferences.getString("current","") + text );
            editor.commit();

        }
        editor.commit();

Result after first save : sharedPreferences.getString("current","") will return "some text" and sharedPreferences.getString("new","") will return ""

Result after changing "first Text" to " new text" : sharedPreferences.getString("current","") will return "new text" and sharedPreferences.getString("new","") will return "first text new text"

how to use it :

  if sharedPreferences.getString("new","") equals ""
your data is not updated  use sharedPreferences.getString("current","")  
else  your data is updated so use sharedPreferences.getString("new","")

这篇关于如何使SharedPreferences更新数据，而不是覆盖数据并丢失部分数据?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！