Question

我在SharedPreference中存储了值，现在我想访问Fragment中的所有内容。当我试图运行我的应用程序时，它崩溃了。

public class Credentials extends Fragment {

Button submit, change;
EditText user, id;
Context ctx;

Context context = getActivity();

 @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {

     View windows = inflater.inflate(R.layout.credential, container, false);
        ((TextView)windows.findViewById(R.id.textView)).setText("Credentials");
        submit = ((Button)windows.findViewById(R.id.submit));
        change = ((Button)windows.findViewById(R.id.change));
        user = ((EditText)windows.findViewById(R.id.username));
        id = ((EditText)windows.findViewById(R.id.Useremail));



    SharedPreferences pref = getActivity().getPreferences(Context.MODE_PRIVATE);
    String username = "";
    String email = "";
    pref.getString("username", username);
    pref.getString("email", email);
    Toast.makeText(getActivity(), "Pressed", Toast.LENGTH_SHORT).show();
    user.setText(username);
    id.setText(email);
}

Answer 1

我为SharedPreference创建了一个Util类，希望它能帮到你。

import android.app.Activity;
import android.content.Context;
import android.content.SharedPreferences;

public class SharedPrefrenceUtils {
    public static final String SHARED_PREFERENCE_TAG="TAG_NAME";

    private SharedPrefrenceUtils(){
         throw new AssertionError();
    }

    public static String getString(Context mContext, String key){
        SharedPreferences pref = mContext.getSharedPreferences(SHARED_PREFERENCE_TAG,Activity.MODE_PRIVATE);
        return pref.getString(key, null);
    }

    public static String getString(Context mContext, String key,  String defaultValue){
        SharedPreferences pref = mContext.getSharedPreferences(SHARED_PREFERENCE_TAG,Activity.MODE_PRIVATE);
        return pref.getString(key, defaultValue);
    }

    public static void putString(Context mContext, String key, String value ){
        SharedPreferences pref= mContext.getSharedPreferences(SHARED_PREFERENCE_TAG, Activity.MODE_PRIVATE);
        SharedPreferences.Editor editor = pref.edit();
        editor.putString(key, value);
        editor.commit();
    }


    public static int getInt(Context mContext, String key){
        SharedPreferences pref = mContext.getSharedPreferences(SHARED_PREFERENCE_TAG,Activity.MODE_PRIVATE);
        return pref.getInt(key, 0);
    }

    public static int getInt(Context mContext, String key,  int defaultValue){
        SharedPreferences pref = mContext.getSharedPreferences(SHARED_PREFERENCE_TAG,Activity.MODE_PRIVATE);
        return pref.getInt(key, defaultValue);
    }

    public static void putInt(Context mContext, String key, int value ){
        SharedPreferences pref= mContext.getSharedPreferences(SHARED_PREFERENCE_TAG, Activity.MODE_PRIVATE);
        SharedPreferences.Editor editor = pref.edit();
        editor.putInt(key, value);
        editor.commit();
    }

    public static long getLong(Context mContext, String key){
        SharedPreferences pref = mContext.getSharedPreferences(SHARED_PREFERENCE_TAG,Activity.MODE_PRIVATE);
        return pref.getLong(key, 0);
    }

    public static long getLong(Context mContext, String key,  long defaultValue){
        SharedPreferences pref = mContext.getSharedPreferences(SHARED_PREFERENCE_TAG,Activity.MODE_PRIVATE);
        return pref.getLong(key, defaultValue);
    }

    public static void putLong(Context mContext, String key, long value ){
        SharedPreferences pref= mContext.getSharedPreferences(SHARED_PREFERENCE_TAG, Activity.MODE_PRIVATE);
        SharedPreferences.Editor editor = pref.edit();
        editor.putLong(key, value);
        editor.commit();
    }


    public static boolean getBoolean(Context mContext, String key){
        SharedPreferences pref = mContext.getSharedPreferences(SHARED_PREFERENCE_TAG,Activity.MODE_PRIVATE);
        return pref.getBoolean(key, false);
    }

    public static boolean getBoolean(Context mContext, String key,  boolean defaultValue){
        SharedPreferences pref = mContext.getSharedPreferences(SHARED_PREFERENCE_TAG,Activity.MODE_PRIVATE);
        return pref.getBoolean(key, defaultValue);
    }

    public static void putBoolean(Context mContext, String key, boolean value ){
        SharedPreferences pref= mContext.getSharedPreferences(SHARED_PREFERENCE_TAG, Activity.MODE_PRIVATE);
        SharedPreferences.Editor editor = pref.edit();
        editor.putBoolean(key, value);
        editor.commit();
    }

    public static void remove(Context mContext, String key){
            SharedPreferences pref= mContext.getSharedPreferences(SHARED_PREFERENCE_TAG, Activity.MODE_PRIVATE);
            SharedPreferences.Editor editor = pref.edit();
            editor.remove(key);
            editor.commit();
    }

    public static void clear(Context mContext){
            SharedPreferences pref= mContext.getSharedPreferences(SHARED_PREFERENCE_TAG, Activity.MODE_PRIVATE);
            SharedPreferences.Editor editor = pref.edit();
            editor.clear();
            editor.commit();
    }

}

现在存储字符串值：在片段中使用以下语句

SharedPrefrenceUtils.putString(mContext,"username", "1234");
SharedPrefrenceUtils.putString(mContext,"email", "xyz@gmail.com");

获取字符串值：在片段中使用以下语句

String userName = SharedPrefrenceUtils.getString(mContext,"username");
String email = SharedPrefrenceUtils.getString(mContext,"email");

您可以从应用程序的任何片段或活动中存储和检索任何其他值。

Answer 2

您的接收方法存在问题。

public abstract String getString（String key，String defValue）

从首选项中检索字符串值。

<强>参数

键：要检索的首选项的名称    defValue ：如果此首选项不存在，则返回值。

退货

返回首选项值（如果存在）或defValue。抛出   如果存在不具有此名称的首选项，则为ClassCastException   一个字符串。

因此，当您使用pref.getString()方法时，您必须将返回值存储为某些内容。

尝试以下示例。

String username = pref.getString("username", "EMPTY");
Toast.makeText(getActivity(), "Value : "+username, Toast.LENGTH_SHORT).show();

如何在Fragment中显示SharedPreference存储的数据？

2 个答案: