Question

我试图从SharedPreferences首选项中获取一个字符串，然后将其放回另一个SharedPreferences首选项中。

来自第一个偏好的getString（）＆＃34; test1＆＃34;并使用putStringSet（）将其添加到第二个首选项。

示例代码：

void test()
{
    Log.v("Main", "********");

    final SharedPreferences test1 = context.getSharedPreferences("test1", MODE_PRIVATE);
    final SharedPreferences.Editor editor1 = test1.edit();
    editor1.clear();
    editor1.putString("sample1", "This is a test");
    editor1.apply();

    final SharedPreferences test2 = context.getSharedPreferences("test2", MODE_PRIVATE);
    final Set<String> set = new HashSet<>(test2.getStringSet("sample2", new HashSet<String>()));

    Log.v("Main", "set.size: " + set.size());

    Log.v("Main", test1.getString("sample1", null));
    set.add(new String(test1.getString("sample1", null)));

    Log.v("Main", "set.size: " + set.size());

    final SharedPreferences.Editor editor2 = test2.edit();
    editor2.clear();
    editor2.putStringSet("sample2", set);
    editor2.apply();
}

运行代码3次会导致：

V/Main﹕ ********
V/Main﹕ set.size: 0
V/Main﹕ This is a test
V/Main﹕ set.size: 1
V/Main﹕ ********
V/Main﹕ set.size: 1
V/Main﹕ This is a test
V/Main﹕ set.size: 1
V/Main﹕ ********
V/Main﹕ set.size: 1
V/Main﹕ This is a test
V/Main﹕ set.size: 1

预期的结果是每次调用都会增加第二个首选项，因为我们正在添加Set eg。

V/Main﹕ ********
V/Main﹕ set.size: 0
V/Main﹕ This is a test
V/Main﹕ set.size: 1
V/Main﹕ ********
V/Main﹕ set.size: 1
V/Main﹕ This is a test
V/Main﹕ set.size: 2
V/Main﹕ ********
V/Main﹕ set.size: 2
V/Main﹕ This is a test
V/Main﹕ set.size: 3

我已经通过getStringSet复制了来自第二个首选项的Set，以避免指向同一个对象。

问题在于Set.add（getString（））。如果我使用普通的字符串，例如Set.add（＆＃34; text＆＃34;），它会工作。我试图创建另一个字符串副本，例如set.add（new String（getString ....但是这也不起作用。

我已经尝试过清理编辑器或使用commit（）而不是apply（）而没有运气。

感谢任何帮助

Answer 1

好吧，我知道到底发生了什么！ 设置基本上不会允许冗余！请阅读documentation。它说

将指定的对象添加到此集合中。如果已经包含对象，则不会修改该集。

因此，如果您尝试添加已存在的同一对象，则不会对其进行修改。

您需要添加已经存在的新对象！所以我尝试了这段代码，它对我有用！

void test(int count) //count is nothing but number of iteration of loop
{
    Log.v("Main", "********");

    final SharedPreferences test1 = getSharedPreferences("test1", MODE_PRIVATE);
    final SharedPreferences.Editor editor1 = test1.edit();
    editor1.clear();
    editor1.putString("sample1", "This is a test");
    editor1.apply();

    final SharedPreferences test2 = getSharedPreferences("test2", MODE_PRIVATE);
    final Set<String> set = test2.getStringSet("sample2", new HashSet<String>()); // Edited this line (Removed new HashSet<>) If you do then it creates new object each time. 

    Log.v("Main", "set.size: " + set.size());

    Log.v("Main", test1.getString("sample1", null));

    set.add(test1.getString("sample1" + " " + count, null) + " --- " + count); // along with the text I'm adding count so the object (string) are not same

    Log.v("Main", "set.size: " + set.size());

    final SharedPreferences.Editor editor2 = test2.edit();
    editor2.clear();
    editor2.putStringSet("sample2", set);
    editor2.apply();
}

输出是：

V/Main﹕ ********
V/Main﹕ set.size: 0
V/Main﹕ This is a test
V/Main﹕ set.size: 1
V/Main﹕ ********
V/Main﹕ set.size: 1
This is a test
V/Main﹕ set.size: 2
V/Main﹕ ********
V/Main﹕ set.size: 2
V/Main﹕ This is a test
V/Main﹕ set.size: 3
V/Main﹕ ********
V/Main﹕ set.size: 3
V/Main﹕ This is a test
V/Main﹕ set.size: 4
V/Main﹕ ********
V/Main﹕ set.size: 4
V/Main﹕ This is a test
V/Main﹕ set.size: 5

并替换

行

final HashSet set = new HashSet<>(test2.getStringSet("sample2", new HashSet<String>()));

带

final HashSet set = test2.getStringSet("sample2", new HashSet<String>());

android SharedPreferences中的Set.add（）没有按预期工作

1 个答案: