Question

获取错误，对于这种类型的sharedPreferences编辑器，未定义方法put double.Eclipse给编辑器一个快速修复添加强制转换，但是当我这样做时它仍然给出错误，为什么我不能放双。

代码：

@Override
protected void onPause() {
    // TODO Auto-generated method stub
    super.onPause();

    if (TextUtils.isEmpty(editBl.getText().toString())) {
        numberOfBl = 0;
    } else {
        numberOfBl = Integer.parseInt(editBl.getText().toString();

    }
    if (TextUtils.isEmpty(editSt.getText().toString())) {
        tonOfSt = 0;
    } else {
        tonOfSt = Double.parseDouble(editSt.getText().toString());

    }

    SharedPreferences prefs = getSharedPreferences(
            "SavedTotals", Context.MODE_PRIVATE);

    SharedPreferences.Editor editor = prefs.edit();

    editor.putInt("savedBl", numberOfBl);
    editor.putDouble("savedSt", tonOfSt);


    editor.commit();
}

Answer 1

那些建议使用 putFloat 和 getFloat 的人很遗憾是非常错误的。将double转换为float可导致

精度不足
溢出
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死小猫

那些暗示 toString 和 parseString 的人没有错，但这是一个效率低下的解决方案。

处理这个问题的正确方法是将double转换为其'raw long bits'等效值并存储该long。当您读取该值时，请转换回double。

因为两种数据类型具有相同的大小，所以不会丢失精度，也不会导致{over，under}流。

Editor putDouble(final Editor edit, final String key, final double value) {
   return edit.putLong(key, Double.doubleToRawLongBits(value));
}

double getDouble(final SharedPreferences prefs, final String key, final double defaultValue) {
return Double.longBitsToDouble(prefs.getLong(key, Double.doubleToLongBits(defaultValue)));
}

或者你可以把getter写成：

double getDouble(final SharedPreferences prefs, final String key, final double defaultValue) {
if ( !prefs.contains(key))
        return defaultValue;

return Double.longBitsToDouble(prefs.getLong(key, 0));
}

Answer 2

Kotlin扩展方式（比使用奇怪的utils类或其他任何东西更漂亮）

fun SharedPreferences.Editor.putDouble(key: String, double: Double) =
    putLong(key, java.lang.Double.doubleToRawLongBits(double))

fun SharedPreferences.getDouble(key: String, default: Double) =
    java.lang.Double.longBitsToDouble(getLong(key, java.lang.Double.doubleToRawLongBits(default)))

Answer 3

我所做的是将首选项保存为字符串：

getSharedPreferences("PREFERENCE", MODE_PRIVATE).edit().putString("double", "0.01").commit();

然后要检索double，只需使用Double.parseDouble：

Double.parseDouble(getSharedPreferences("PREFERENCE", MODE_PRIVATE).getString("double", "0.01"));

Answer 4

你总是可以实现SharedPreferences并包装android实现。

package com.company.sharedpreferences;

import android.content.Context;
import android.content.SharedPreferences;


import java.util.Map;
import java.util.Set;

public class EnhancedSharedPreferences implements SharedPreferences {

    public static class NameSpaces {
        public static String MY_FUN_NAMESPACE = "MyFunNameSpacePrefs";
    }

    public static EnhancedSharedPreferences getPreferences(String prefsName) {
        return new EnhancedSharedPreferences(SomeSingleton.getInstance().getApplicationContext().getSharedPreferences(prefsName, Context.MODE_PRIVATE));
    }

    private SharedPreferences _sharedPreferences;

    public EnhancedSharedPreferences(SharedPreferences sharedPreferences) {
        _sharedPreferences = sharedPreferences;
    }

    //region Overrides

    @Override
    public Map<String, ?> getAll() {
        return _sharedPreferences.getAll();
    }

    @Override
    public String getString(String key, String defValue) {
        return _sharedPreferences.getString(key, defValue);
    }

    @Override
    public Set<String> getStringSet(String key, Set<String> defValues) {
        return _sharedPreferences.getStringSet(key, defValues);
    }

    @Override
    public int getInt(String key, int defValue) {
        return _sharedPreferences.getInt(key, defValue);
    }

    @Override
    public long getLong(String key, long defValue) {
        return _sharedPreferences.getLong(key, defValue);
    }

    @Override
    public float getFloat(String key, float defValue) {
        return _sharedPreferences.getFloat(key, defValue);
    }

    @Override
    public boolean getBoolean(String key, boolean defValue) {
        return _sharedPreferences.getBoolean(key, defValue);
    }

    @Override
    public boolean contains(String key) {
        return _sharedPreferences.contains(key);
    }

    @Override
    public Editor edit() {
        return new Editor(_sharedPreferences.edit());
    }

    @Override
    public void registerOnSharedPreferenceChangeListener(OnSharedPreferenceChangeListener listener) {
        _sharedPreferences.registerOnSharedPreferenceChangeListener(listener);
    }

    @Override
    public void unregisterOnSharedPreferenceChangeListener(OnSharedPreferenceChangeListener listener) {
        _sharedPreferences.unregisterOnSharedPreferenceChangeListener(listener);
    }

    //endregion

    //region Extension

    public Double getDouble(String key, Double defValue) {
        return Double.longBitsToDouble(_sharedPreferences.getLong(key, Double.doubleToRawLongBits(defValue)));
    }

    //endregion

    public static class Editor implements SharedPreferences.Editor {

        private SharedPreferences.Editor _editor;

        public Editor(SharedPreferences.Editor editor) {
            _editor = editor;
        }

        private Editor ReturnEditor(SharedPreferences.Editor editor) {
            if(editor instanceof Editor)
                return (Editor)editor;
            return new Editor(editor);
        }

        //region Overrides

        @Override
        public Editor putString(String key, String value) {
            return ReturnEditor(_editor.putString(key, value));
        }

        @Override
        public Editor putStringSet(String key, Set<String> values) {
            return ReturnEditor(_editor.putStringSet(key, values));
        }

        @Override
        public Editor putInt(String key, int value) {
            return ReturnEditor(_editor.putInt(key, value));
        }

        @Override
        public Editor putLong(String key, long value) {
            return ReturnEditor(_editor.putLong(key, value));
        }

        @Override
        public Editor putFloat(String key, float value) {
            return ReturnEditor(_editor.putFloat(key, value));
        }

        @Override
        public Editor putBoolean(String key, boolean value) {
            return ReturnEditor(_editor.putBoolean(key, value));
        }

        @Override
        public Editor remove(String key) {
            return ReturnEditor(_editor.remove(key));
        }

        @Override
        public Editor clear() {
            return ReturnEditor(_editor.clear());
        }

        @Override
        public boolean commit() {
            return _editor.commit();
        }

        @Override
        public void apply() {
            _editor.apply();
        }

        //endregion

        //region Extensions

        public Editor putDouble(String key, double value) {
            return new Editor(_editor.putLong(key, Double.doubleToRawLongBits(value)));
        }

        //endregion
    }
}

Answer 5

检查这个要点https://gist.github.com/john1jan/b8cb536ca51a0b2aa1da4e81566869c4

我创建了一个Preference Utils类来处理所有情况。

易于使用

存储到首选项

PrefUtils.saveToPrefs(getActivity(), PrefKeys.USER_INCOME, income);

从偏好中获取

Double income = (Double) PrefUtils.getFromPrefs(getActivity(), PrefKeys.USER_INCOME, new Double(10));

Answer 6

在 Kotlin 中，您可以将指定浮点值的位表示形式的双精度值转换为 Long，然后使用 putLong() 方法将该位表示形式保存在共享首选项中。当您想从共享首选项中获取该值时，只需使用 Double.fromBits() 方法将其转换为 Double 值，您将获得一个没有精度损失的 double 值。您可以阅读更多相关信息here。

以下是我在共享首选项中使用纬度和经度作为双精度值的示例：

    val lat: Double = 40.23244412709637
    val lng: Double = 14.280891281901097
    
     private fun saveFetchedLocation(lat: Double, lng: Double) {
            val sharedPreference: SharedPreferences = requireActivity().getSharedPreferences(
                SHARED_PREF,
                Context.MODE_PRIVATE
            )
            val editor: SharedPreferences.Editor = sharedPreference.edit()
            editor.apply {
                putLong("lat_value", lat.toBits())
                putLong("lng_val", lng.toBits())
     
            Log.i("Tag", "LONG_BITS: "+ " Lat: " + lat.toBits() + " Lng: " + lng.toBits())
    
            }.apply()
    
        }
    
    private fun loadPreferences() {
            val sharedPreference: SharedPreferences = requireActivity().getSharedPreferences(
                SHARED_PREF,
                Context.MODE_PRIVATE
            )
            val lat_double: Double = Double.fromBits(sharedPreference.getLong("lat_value", 1))
            val lng_double: Double = Double.fromBits(sharedPreference.getLong("lng_val", 1))
    
            Log.i("Tag", "FINAL_DOUBLE: $lat_double and $lng_double")
    
        }

Logcat 结果：

//bit representation of the specified floating-point values as Long
I/Tag: LONG_BITS:  Lat: 4630859030446343002 Lng: 4624229045136719443 

//converted double values with no precision loss
I/Tag: FINAL_DOUBLE: 40.23244412709637 and 14.280891281901097

不能把双SharedPreferences

6 个答案: