android - OnPreferenceChangeListener 在进行更改之前触发

Question

对于下面的代码:

final SwitchPreference sp = (SwitchPreference) findPreference(getString(R.string.pref_key_reminder));
        sp.setOnPreferenceChangeListener(new Preference.OnPreferenceChangeListener() {
            @Override
            public boolean onPreferenceChange(Preference preference, Object o) {
                AlarmReceiver.scheduleAlarm(getActivity());
                return true;
            }
        });

我需要switch preference的改变值，但是preferance中的值是改变前的值。对象 o 具有新值，但如何在调用 AlarmReceiver.scheduleAlarm 之前在首选项中设置它。该方法使用首选项的值。

Answer 1

你是对的，SwitchPreference 更改了底层 SharedPreferences 值之后 Preference.OnPreferenceChangeListener.onPreferenceChange 是调用，请参阅 SwitchPreference 中的代码:

private class Listener implements CompoundButton.OnCheckedChangeListener {
    @Override
    public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
        if (!callChangeListener(isChecked)) { // callback here
            // Listener didn't like it, change it back.
            // CompoundButton will make sure we don't recurse.
            buttonView.setChecked(!isChecked);
            return;
        }

        SwitchPreference.this.setChecked(isChecked); // save value here
    }
}

/**
 * Sets the checked state and saves it to the {@link SharedPreferences}.
 *
 * @param checked The checked state.
 */
public void setChecked(boolean checked) {
    // Always persist/notify the first time; don't assume the field's default of false.
    final boolean changed = mChecked != checked;
    if (changed || !mCheckedSet) {
        mChecked = checked;
        mCheckedSet = true;
        persistBoolean(checked);
        if (changed) {
            notifyDependencyChange(shouldDisableDependents());
            notifyChanged();
        }
    }
}

然后当你打电话时:

AlarmReceiver.scheduleAlarm(getActivity());

并从 SharedPreferences 中检索值，您将获得旧值。因此，您可以推迟对 AlarmReceiver.scheduleAlarm 的调用，例如，使用 Handler:

handler.post(new Runnable() {
    AlarmReceiver.scheduleAlarm(getActivity());
});