如何從另一個類中獲取SharedPreference中的數據？

Question

我試圖獲取存儲在另一個類的共享偏好數據，

public class MyActivity_Settings extends ListActivity { 


       //Shared Preference 
       SharedPreferences mSharedPreferences; 
       public static final String MYPREFERENCES = "MyUserChoice"; 
       public ArrayList<String> selectedItems = new ArrayList<>(); 

//onCreate 
    mSharedPreferences = getSharedPreferences(MYPREFERENCES, Context.MODE_PRIVATE); 

     @Override 
      public void finish() { 

     String selected = "My string" 

       SharedPreferences.Editor prefEditor = mSharedPreferences.edit(); 
       prefEditor.putString(MYPREFERENCES, selected); 
       prefEditor.apply(); 
       super.finish(); 
      } 

所以，從另一個類我要檢查是否爲MyPreference有一些數據，也基本上使用這些數據，這樣我可以進一步代碼

我想要做這樣的事情

if (mSharedPreferences.contains(MYPREFERENCES)) { 
      String savedItems = mSharedPreferences.getString(MYPREFERENCES, ""); 
      selectedItems.addAll(Arrays.asList(savedItems.split(","))); 

這是另一項活動

MyActivity_Settings mMyActivity_settings = new MyActivity_Settings(); 

public class MainActivity extends AppCompatActivity{ 
    protected void onCreate(Bundle savedInstanceState) { 
      super.onCreate(savedInstanceState); 

    //Obviously this is not working 

    if(mMyActivity_settings.mSharedPreferences.contains(mMyActivity_settings.MYPREFERENCES){ 

Toast.makeText(this, " From MainACTIVITY WE HAVE DATA",Toast.LENGTH_LONG).show(); 
      } 


    } 

    } 

Answer 1

從其他類（活動），你應該爲了重視這個代碼把你SharedPreferences：

SharedPreferences sharedPref; sharedPref = getSharedPreferences(MYPREFERENCESKEY , Context.MODE_PRIVATE); String selected = sharedPref.getString("MyUserChoice","");

你也尚未初始化SharedPreferences實例，您應該在當前活動中像這樣初始化它

SharedPreferences sharedPref; 
sharedPref = getSharedPreferences(MYPREFERENCESKEY , Context.MODE_PRIVATE) 

如果要檢查，如果你 SharedPreferences有數據，你可以檢查 SharedPreference與鍵值 MyUserChoice已，爲了不與空白 String值相等

。正如您在sharedPref.getString("MyUserChoice","");中看到的，第二個參數是您沒有任何數據時的默認值。檢查正確的方法是這樣的 if(str != null && !str.isEmpty())

Answer 2

在其他活動，你可以使用reget的sharedprefs：

mSharedPreferences = gettApplicationContext().getSharedPreferences(SHARED_PREFERENCES_NAME, Context.MODE_PRIVATE); 

，並檢查有：

mSharedPreferences.contains(KEY); 

編輯：添加完整的例子爲清楚：

1日活動

private final static String MYPREFERENCES = "myapppref";//pref file name 
    private final static String MY_PREF_KEY = "timesclicked";//a key for the sharedpref map key->value 

    public void onCreate(Bundle savedInstanceState){ 
     [do usual stuff layout and so on...] 
     //first argument is the preference filename, if not existing it will be created, you can use a lot of different files if you need to 
     SharedPreference mSharedPreferences = getSharedPreferences(MYPREFERENCES, Context.MODE_PRIVATE); 
     //store a value to this pref file, in this case a key MY_PREF_KEY is a costant, value is what you want to store 
     mSharedPreferences.edit().putString(MY_PREF_KEY, value).apply(); 
    } 

第二幕ivity

public void checkMyPrefKeyExistance(){ 
    //get the pref file with the same name as first activity 
    SharedPreference mSharedPreferences = getSharedPreferences(MYPREFERENCES, Context.MODE_PRIVATE); 
    //check if key exists 
    boolean hasKey = mSharedPreferences.contains(KEY); 
    //get value for key, or default value, in this case def val is empty string 
    mSharedPreferences.getString(MY_PREF_KEY, ""); 
} 

https://developer.android.com/reference/android/content/Context.html#getSharedPreferences(java.lang.String，INT）

Answer 3

在大多數應用中，我創建MyApp擴展Application類。 我在MyApp類中編寫了大部分SharePreference方法。

public static String getUsername() { 
     SharedPreferences mAppPreferences = PreferenceManager 
       .getDefaultSharedPreferences(context); 
     return mAppPreferences.getString("USERNAME", ""); 
    } 

public static void setUsername(String username) { 
     SharedPreferences mAppPreferences = PreferenceManager 
       .getDefaultSharedPreferences(context); 
     Editor mEditor = mAppPreferences.edit(); 
     mEditor.putString("USERNAME", username); 
     mEditor.commit(); 
    } 

因此，您可以輕鬆地在每個活動中獲取或設置數據。 獲取數據，只需撥打：

MyApp.getUsername(); 

設定資料，請致電：

MyApp.setUsername("Your User Name"); 

希望，這將幫助你。