Android PreferenceManager.setDefaultValues() 因类转换异常而崩溃

Question

我有一个令人沮丧的问题，我已经使用支持库为 Android 创建了自定义首选项。

public class CustomTimePreference extends DialogPreference {
    public int hour = 0;
    public int minute = 0;

    public CustomTimePreference(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public static int parseHour(String value) {
        try {
            String[] time = value.split(":");
            return (Integer.parseInt(time[0]));
        } catch (Exception e) {
            return 0;
        }
    }

    public static int parseMinute(String value) {
        try {
            String[] time = value.split(":");
            return (Integer.parseInt(time[1]));
        } catch (Exception e) {
            return 0;
        }
    }

    public static String timeToString(int h, int m) {
        return String.format("%02d", h) + ":" + String.format("%02d", m);
    }


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

    @Override
    protected void onSetInitialValue(boolean restoreValue, Object defaultValue) {
        String value;
        if (restoreValue) {
            if (defaultValue == null) value = getPersistedString("00:00");
            else value = getPersistedString(defaultValue.toString());
        } else {
            value = defaultValue.toString();
        }

        hour = parseHour(value);
        minute = parseMinute(value);
    }


    public void persistStringValue(String value) {
        persistString(value);
    }
}

和

public class CustomTimePreferenceDialogFragmentCompat extends PreferenceDialogFragmentCompat implements DialogPreference.TargetFragment {
    TimePicker timePicker = null;

    @Override
    protected View onCreateDialogView(Context context) {
        timePicker = new TimePicker(context);
        return (timePicker);
    }

    @Override
    protected void onBindDialogView(View v) {
        super.onBindDialogView(v);
        timePicker.setIs24HourView(true);
        CustomTimePreference pref = (CustomTimePreference) getPreference();
        timePicker.setCurrentHour(pref.hour);
        timePicker.setCurrentMinute(pref.minute);
    }

    @Override
    public void onDialogClosed(boolean positiveResult) {
        if (positiveResult) {
            CustomTimePreference pref = (CustomTimePreference) getPreference();
            pref.hour = timePicker.getCurrentHour();
            pref.minute = timePicker.getCurrentMinute();

            String value = CustomTimePreference.timeToString(pref.hour, pref.minute);
            if (pref.callChangeListener(value)) pref.persistStringValue(value);
        }
    }

    @Override
    public Preference findPreference(CharSequence charSequence) {
        return getPreference();
    }
}

为了完整起见，preferences.xml 中包含的 xml 是:

<customcontrols.CustomTimePreference
            android:key="time_pace_preference"
            android:title="@string/title_time_pace_preference"
            android:defaultValue="@string/settings_default_pace"
            android:summary="Set some time"
            />

但是，当我尝试调用

PreferenceManager.setDefaultValues(mContext, preferences, true);

我收到了

java.lang.ClassCastException: customcontrols.CustomTimePreference cannot be cast to android.preference.Preference

为什么会这样？由于 CustomTimePreference 扩展了 DialogPreference，而 DialogPreference 本身又扩展了 Preference，这应该没问题吧？!

如果我不调用 setDefaultValues()，我可以进入我的设置 fragment 并查看自定义控件吗？

我做错了什么，我该如何解决!？

Answer 1

如果您正在扩展 android.support.v7.preference.DialogPreference 将导致此崩溃。

如果是这样，您可以改用 android.support.v7.preference.PreferenceManager#setDefaultValues(android.content.Context, int, boolean)。