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android - Android：启动应用程序时保存的InstanceState为空

问题描述

savedInstanceState == nullAndroid ：当我重新启动我的应用程序时，我总是有。我有一个片段，我想在停止应用程序后存储/重用数据。

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setHasOptionsMenu(true);
    mPrefs = android.preference.PreferenceManager.getDefaultSharedPreferences(getActivity());

    if (savedInstanceState != null) {
        mLoading = savedInstanceState.getBoolean(OUTSTATE_LOADING, false);
        mCurrentFiliere = savedInstanceState.getInt(OUTSTATE_CURRENT_FILIERE, 0);
    }
}

@Override
public void onSaveInstanceState(@NonNull Bundle savedInstanceState) {
    super.onSaveInstanceState(savedInstanceState);
    savedInstanceState.putInt(OUTSTATE_CURRENT_FILIERE, mCurrentFiliere);
}

@Override
public void onViewStateRestored(@Nullable Bundle savedInstanceState) {
    super.onViewStateRestored(savedInstanceState);
    if (savedInstanceState != null) {
        mCurrentFiliere = savedInstanceState.getInt(OUTSTATE_CURRENT_FILIERE);
    }
}

方法onCreate和onViewStateRestored返回null

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@android:id/list"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <ProgressBar
        android:id="@android:id/progress"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:indeterminate="true"
        android:visibility="gone" />
</FrameLayout>

而且我在其他帖子中没有找到任何答案...

标签： androidonsaveinstancestate

解决方案

您可能了解Activity Lifecycle，为了避免在方向更改、接听电话等时 Instance Sate 之间的数据松散，请使用SaveInstanceState. 否则使用shared preferences.

节省-

SharedPreferences pref = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
                        SharedPreferences.Editor editor = pref.edit();
                        editor.putString("testkey", "testvalue");
                        editor.commit();

要得到-

SharedPreferences defPref = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
        String restore  = defPref.getString("testkey","");

示例类-

public class MainActivity extends AppCompatActivity {
private Button add;
private TextView textView;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    add = (Button) findViewById(R.id.add);
    textView = findViewById(R.id.textviewYear);

    SharedPreferences defPref = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
    String restore  = defPref.getString("testkey","");
    textView.setText(restore);



    add.setOnClickListener(new View.OnClickListener() {
        @RequiresApi(api = Build.VERSION_CODES.O)
        @Override
        public void onClick(View v) {
            SharedPreferences pref = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
            SharedPreferences.Editor editor = pref.edit();
            editor.putString("testkey", "testvalue");
            editor.commit();
        }
    });
}
 }

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