android - 使用 NumberPicker 作为 DialogPreference。为什么我的设置不保存？

Question

只是在这里学习android代码。我不确定我遗漏了什么，但我正在尝试创建一个自定义 DialogPreference，它使用 NumberPicker 让用户选择年份。我试着关注安卓的 Settings Guide ，但我选择的值不会保存。只要我不退出应用程序，它就会保存，但如果我退出，那么当我重新启动应用程序时，它会重置为默认值。我错过了什么？

设置 Activity 代码:

public class SettingsActivity extends PreferenceActivity {

    @Override
      public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        getFragmentManager().beginTransaction().replace(android.R.id.content, new MyPreferenceFragment()).commit();

      }

    public static class MyPreferenceFragment extends PreferenceFragment
    {
        @Override
        public void onCreate(final Bundle savedInstanceState)
        {
            super.onCreate(savedInstanceState);
            addPreferencesFromResource(R.xml.app_preferences);
        }
    }
}

app_preferences.xml(SettingsActivity 的布局)

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android" >
    <EditTextPreference />

    <com.NsouthProductions.gradetrackerpro.SemesterPickerPreference
        android:key="MY_PICKER"
        android:title="@string/year_pref_str"
        android:summary="Choose a year here"
        android:defaultValue="2005"
    /> 

</PreferenceScreen>

SemesterPickerPreference(DialogPreference 的扩展)

public class SemesterPickerPreference extends DialogPreference {

    private int year;
    private NumberPicker semPick;
    private int DEFAULT_VALUE;

    public SemesterPickerPreference(Context context, AttributeSet attrs) {
        super(context, attrs);

        DEFAULT_VALUE = 2003;

        setDialogLayoutResource(R.layout.semester_picker_dialog);
        setPositiveButtonText(android.R.string.ok);
        setNegativeButtonText(android.R.string.cancel);

        setDialogIcon(null);
    }

    @Override
    protected void onDialogClosed(boolean positiveResult) {

        if (positiveResult) {
            persistInt(semPick.getValue());
        }
    }

    @Override
    protected void onSetInitialValue(boolean restorePersistedValue, Object defaultValue) {
        if (restorePersistedValue) {
            // Restore existing state
            year = this.getPersistedInt(DEFAULT_VALUE);
        } else {
            // Set default state from the XML attribute
            year = (Integer) defaultValue;
            persistInt(year);
        }
    }

    @Override
    protected Object onGetDefaultValue(TypedArray a, int index) {
        return a.getInteger(index,  DEFAULT_VALUE);
    }

    @Override
    protected View onCreateDialogView() {

        int max = 2038;
        int min = 2001;

        LayoutInflater inflater =
                (LayoutInflater) getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        View view = inflater.inflate(R.layout.semester_picker_dialog, null);

        semPick = (NumberPicker) view.findViewById(R.id.semester_picker);

        // Initialize state
        semPick.setMaxValue(max);
        semPick.setMinValue(min);
        semPick.setValue(this.getPersistedInt(DEFAULT_VALUE));
        semPick.setWrapSelectorWheel(false);

        return view;
    }



    //  This code copied from android's settings guide.

    private static class SavedState extends BaseSavedState {
        // Member that holds the setting's value
        // Change this data type to match the type saved by your Preference
        int value;

        public SavedState(Parcelable superState) {
            super(superState);
        }

        public SavedState(Parcel source) {
            super(source);
            // Get the current preference's value
            value = source.readInt();  // Change this to read the appropriate data type
        }

        @Override
        public void writeToParcel(Parcel dest, int flags) {
            super.writeToParcel(dest, flags);
            // Write the preference's value
            dest.writeInt(value);  // Change this to write the appropriate data type
        }

        // Standard creator object using an instance of this class
        public static final Parcelable.Creator<SavedState> CREATOR =
                new Parcelable.Creator<SavedState>() {

            public SavedState createFromParcel(Parcel in) {
                return new SavedState(in);
            }

            public SavedState[] newArray(int size) {
                return new SavedState[size];
            }
        };
    }



    @Override
    protected Parcelable onSaveInstanceState() {
        final Parcelable superState = super.onSaveInstanceState();
        // Check whether this Preference is persistent (continually saved)
        if (isPersistent()) {
            // No need to save instance state since it's persistent, use superclass state
            return superState;
        }

        // Create instance of custom BaseSavedState
        final SavedState myState = new SavedState(superState);
        // Set the state's value with the class member that holds current setting value
        myState.value = year;
        return myState;
    }

    @Override
    protected void onRestoreInstanceState(Parcelable state) {
        // Check whether we saved the state in onSaveInstanceState
        if (state == null || !state.getClass().equals(SavedState.class)) {
            // Didn't save the state, so call superclass
            super.onRestoreInstanceState(state);
            return;
        }

        // Cast state to custom BaseSavedState and pass to superclass
        SavedState myState = (SavedState) state;
        super.onRestoreInstanceState(myState.getSuperState());

        // Set this Preference's widget to reflect the restored state
        semPick.setValue(myState.value);
    }
}

semester_picker_dialog.xml(我的学期/年级选择器的布局)

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="match_parent"
    android:orientation="horizontal" 
    android:gravity="center_horizontal" >

    <NumberPicker
        android:id="@+id/semester_picker"
        android:layout_centerInParent="true"
        android:layout_width="100dip"
        android:layout_height="match_parent" />

</LinearLayout>

Answer 1

你错过了 android:persistent="true"您首选项 XML 中的 XML 属性。这就是告诉首选项是否实际将其值存储到共享首选项的原因。调用 PersistInt() 显然是不够的。