PreferenceFragment.findPreference 总是返回 NULL [英] PreferenceFragment.findPreference always returns NULL

问题描述

我目前正在尝试制作一个设置菜单，它将显示一个MultiSelectListPreference，以从您的联系人列表中选择多个联系人.

I'm currently trying to make a settings menu, that will show a MultiSelectListPreference, to select multiple contacts from your contact list.

此时，我收到 NullPointerException，当我尝试 MultiSelectListPreference#setEntryValue(CharSequence[]) 如果我把 setEntries代码> 首先，那个抛出相同的异常.

At this moment, I'm receiving an NullPointerException, when i try to MultiSelectListPreference#setEntryValue(CharSequence[]) If I put the setEntries first, that one throws the same exception.

我已经设置了一个断点，以逐步查看会发生什么.变量被填充是因为它们存储Strings，它们可以包含一个Stringnull"，所以我猜如果没有Display_Name<，它不会失败/code> 可用左右.

I've put a breakpoint, to see step by step what happens. The variables are filled because they store Strings, they can contain a String "null", so I guess that it doesn't fail if there is no Display_Name available or so.

我基于 这个答案

有人有想法吗?如果您需要更多信息，请告诉我.感谢阅读！

Anyone has an idea? If you need more information, tell me. Thanks for reading!

package be.wdk.sendtowork;contactNumberArray

import android.database.Cursor;
import android.os.Bundle;
import android.preference.MultiSelectListPreference;
import android.preference.PreferenceFragment;
import android.provider.ContactsContract;
import android.util.Log;
import android.widget.Toast;

public class PreferenceClass extends PreferenceFragment {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Integer countContacts = 0;

        String[] projection = new String[]{
                ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME,
                ContactsContract.CommonDataKinds.Phone.NUMBER,
                ContactsContract.CommonDataKinds.Phone.PHOTO_URI
        };

        String selection = ContactsContract.CommonDataKinds.Phone.HAS_PHONE_NUMBER;
        String sortOrder = ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME;
        try {
            Cursor c1 = getActivity().getContentResolver().query(ContactsContract.CommonDataKinds.Phone.CONTENT_URI, projection, selection, null, sortOrder);
            c1.moveToFirst();
            Integer c1columncount = c1.getColumnCount();
            Integer c1count = c1.getCount();
            Toast toastje = Toast.makeText(getActivity(), c1columncount.toString() + " - " + c1count.toString(), Toast.LENGTH_SHORT);
            toastje.show();

            CharSequence[] contactNameArray = new CharSequence[c1count], contactNumberArray = new CharSequence[c1count];
            MultiSelectListPreference mslp = (MultiSelectListPreference) findPreference("contactList");
            do {
                contactNameArray[countContacts] = c1.getString(0) + " - " + c1.getString(2);
                contactNumberArray[countContacts] = c1.getString(1);
                countContacts += 1;
            } while(c1.moveToNext());

            mslp.setEntryValues(contactNumberArray); //<- line that throws the error
            mslp.setEntries(contactNameArray);
            addPreferencesFromResource(R.xml.preferences);
        } 
        catch (Exception e) {
            Log.v("TAG", " " + e.toString());
            e.getMessage();
        }
    }
}

好的，我又做了几次检查.-我在我的 XML 中做了一个测试首选项，并使用 findPrefence 使它的一个对象可以使用 -> 返回 NULL- 我已经将我的 MultiSelectListPreference 的键设置为 @string/test，把它放在我的 strings.xml 中，findpreference 仍然返回 Null.

Ok, I did a couple more checks. -I made a test preference in my XML and used the findPrefence to make an object of it to work with -> returns NULL -I have set my key of my MultiSelectListPreference to @string/test, putted this in my strings.xml, findpreference still returns Null.

我的 PreferenceFragment 有问题吗?

Can there be a problem with my PreferenceFragment?

推荐答案

好的，我找到了我的问题所在.

Ok, i found what my problem was.

MultiSelectListPreference mslp = (MultiSelectListPreference) findPreference("contactList"); 

返回NULL，因为

addPreferencesFromResource(R.xml.preferences);

一开始还没有完成......所以它还没有加载我的偏好.

is not done at the start... so it didn't load my preferences in yet.

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