共享首选项存储值在 android onCreate() 中不起作用

Question

在我的应用程序中，我使用共享首选项，它在 onResume() 中工作正常，只是在 onCreate() 中不起作用。有人知道原因吗？在 onCreate 中，共享首选项值始终仅为 null。

这是我的代码

@Override
protected void onResume() {

    setTextValues();
    super.onResume();
    }

private void setTextValues(){       
      txt1.setText(PreferenceConnector.readString(this,PreferenceConnector.MILEAGE, null));
      txt2.setText(PreferenceConnector.readString(this,PreferenceConnector.YEAR, null));
      txt3.setText(PreferenceConnector.readString(this,PreferenceConnector.CAPACITY, null));         
}

   package com.InternetGMBH.Sample.Utilities;

     import com.InternetGMBH.Tample.Activities.WheelActivity;

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

  public class PreferenceConnector{
  public static final String PREF_NAME = "PEOPLE_PREFERENCES";
  public static final int MODE = Context.MODE_PRIVATE;


public static final String MILEAGE= "MILEAGE";
public static final String YEAR= "YEAR";
public static final String CAPACITY= "CAPACITY";



public static void writeBoolean(Context context, String key, boolean value) {
    getEditor(context).putBoolean(key, value).commit();
}

public static boolean readBoolean(Context context, String key, boolean defValue) {
    return getPreferences(context).getBoolean(key, defValue);
}

public static void writeInteger(Context context, String key, int value) {
    getEditor(context).putInt(key, value).commit();

}

public static int readInteger(Context context, String key, int defValue) {
    return getPreferences(context).getInt(key, defValue);
}

public static void writeString(Context context, String key, String value) {
    getEditor(context).putString(key, value).commit();

}

public static String readString(Context context, String key, String defValue) {
    return getPreferences(context).getString(key, defValue);
}

public static void writeFloat(Context context, String key, float value) {
    getEditor(context).putFloat(key, value).commit();
}

public static float readFloat(Context context, String key, float defValue) {
    return getPreferences(context).getFloat(key, defValue);
}

public static void writeLong(Context context, String key, long value) {
    getEditor(context).putLong(key, value).commit();
}

public static long readLong(Context context, String key, long defValue) {
    return getPreferences(context).getLong(key, defValue);
}

public static SharedPreferences getPreferences(Context context) {
    return context.getSharedPreferences(PREF_NAME, MODE);
}



public static Editor getEditor(Context context) {
    return getPreferences(context).edit();
}

}

如果我在 onCreate() 中调用 setTextValues()，它只显示空值。但 onResume 工作正常。

Answer 1

您的 Activity 似乎是您应用程序的第一个 Activity，在 onCreate 方法中 SharedPreferences 可能未正确初始化。

最好在 onStart 方法中使用 Preferences，而不是 onCreate 或 onResume 方法。

Answer 2

SharedPreferences 不同于首选项。您应该像下面的示例代码一样调用 getSharedPreferences：

public static String APP_PREFERENCES = "appPreferences";
public static String PREFERENCE_SAMPLE = "prefSample";

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    //get Shared preferences
    sharedPreferences = getSharedPreferences(APP_PREFERENCES, MODE_PRIVATE);

    //retrieve a preference
    String str = sharedPreferences.getString(PREFERENCE_SAMPLE, "");

}

Answer 3

将此作为共享偏好类

public class PreferenceConnector{
public static final String PREF_NAME = "PEOPLE_PREFERENCES";
public static final int MODE = Context.MODE_PRIVATE;

/*public static final String NAME = "NAME";
public static final String SURNAME = "SURNAME";
public static final String AGE = "AGE";*/

public static void writeBoolean(Context context, String key, boolean value) {
    getEditor(context).putBoolean(key, value).commit();
}

public static boolean readBoolean(Context context, String key, boolean defValue) {
    return getPreferences(context).getBoolean(key, defValue);
}

public static void writeInteger(Context context, String key, int value) {
    getEditor(context).putInt(key, value).commit();

}

public static int readInteger(Context context, String key, int defValue) {
    return getPreferences(context).getInt(key, defValue);
}

public static void writeString(Context context, String key, String value) {
    getEditor(context).putString(key, value).commit();

}

public static String readString(Context context, String key, String defValue) {
    return getPreferences(context).getString(key, defValue);
}

public static void writeFloat(Context context, String key, float value) {
    getEditor(context).putFloat(key, value).commit();
}

public static float readFloat(Context context, String key, float defValue) {
    return getPreferences(context).getFloat(key, defValue);
}

public static void writeLong(Context context, String key, long value) {
    getEditor(context).putLong(key, value).commit();
}

public static long readLong(Context context, String key, long defValue) {
    return getPreferences(context).getLong(key, defValue);
}

public static SharedPreferences getPreferences(Context context) {
    return context.getSharedPreferences(PREF_NAME, MODE);
}

public static Editor getEditor(Context context) {
    return getPreferences(context).edit();
}

}