java SharedReferences在检索值时返回null
当应用程序关闭或被破坏时,我试图将一些带有SharedPreferences
的值保存为键值对,并在再次打开应用程序时检索它们。
问题是,当我调用以检索值时,它返回null
我已经尝试过传递上下文或获取应用程序上下文并生成值static
,但它似乎不起作用
class SavedValues {
private static final String keyP1fName = String.valueOf(R.string.player_1_name_key);
private static final String keyP1Game = String.valueOf(R.string.player_1_game_key);
private static final String keyP2fName = String.valueOf(R.string.player_2_sname_key);
//Have other strings here
private MainGame mainGame;
SavedValues(MainGame mainGame) {
this.mainGame = mainGame;
}
//private SharedPreferences mPrefs = mainGame.getSharedPreferences("myPrefs", Context.MODE_PRIVATE);
private SharedPreferences mPrefs = mainGame.getPreferences(Context.MODE_PRIVATE);
//SharedPreferences mPrefs = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
void saveMainGameValues() {
SharedPreferences.Editor editor = mPrefs.edit();
editor.putString(keyP1fName, mainGame.fullNameP1.getText().toString());
editor.putString(keyP1Game, mainGame.gameScoreP1.getText().toString());
editor.putString(keyP2fName, mainGame.fullNameP2.getText().toString());
editor.putString(keyP2Game, maingGame.gameScoreP2.getText().toString());
editor.apply();
}
void getMainGameValues() {
mPrefs = mainGame.getPreferences(Context.MODE_PRIVATE);
if (mPrefs.contains(keyP1fName)) {
mainGame.fullNameP1.setText(mPrefs.getString(keyP1fName, "Player 1"));
mainGame.gameScoreP1.setText(mPrefs.getString(keyP1Game, "0"));
mainGame.fullNameP2.setText(mPrefs.getString(keyP2fName, "Player 2"));
mainGame.gameScoreP2.setText(mPrefs.getString(keyP2Game, "0"));
}}
}
我试图在我的主要活动的onStart/onStop等方法中调用这些
@Override
protected void onStart() {
//savedVals.getMainGameValues();
super.onStart();
}
@Override
protected void onResume() {
savedVals.getMainGameValues();
super.onResume();
}
@Override
protected void onPause() {
super.onPause();
savedVals.saveMainGameValues();
}
@Override
protected void onStop() {
super.onStop();
savedVals.saveMainGameValues();
}
@Override
protected void onDestroy() {
super.onDestroy();
savedVals.saveMainGameValues();
}
我应该获取最后检索到的值或至少是默认值,但是应用程序崩溃,并在onStart或onResume中获取回调的以下错误:
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.andygix.a40love.SavedValues.getMainGameValues()' on a null object reference
at com.andygix.a40love.MainGame.onResume(MainGame.java:379)
at 安卓.app.Instrumentation.callActivityOnResume(Instrumentation.java:1364)
at 安卓.app.Activity.performResume(Activity.java:7490)
# 1 楼答案
您的
SavedValues
类存在逻辑错误初始化类时,将调用构造函数
mainGame
获得一些值,但在mPref
之前创建变量mPref
,因此它没有值必须在构造函数中初始化mPref
在这里我更新了课程。。试着更换并检查
希望对你有帮助