Question

好的，我知道之前有过很多关于Android中的SharedPreferences的问题，而且我确实设法走得很远，但是因为我对SharedPreferences有点新意，所以我不知道最后几步要做什么它起作用。

在我的MainActivity中，我有以下内容：

public class MainActivity extends ActionBarActivity
{
    ...

    // Public static MainActivity so we can use findViewById from MyPrefsActivity
    public static MainActivity mActivity;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        ...

        mActivity = this;
    }

    ...

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        switch(id){
            case R.id.action_settings:
                startActivity(new Intent(this, MyPrefsActivity.class));
                return true;
        }
        return false;
    }
}

这是MyPrefsActivity.java：

package com.example.checkboxoptionsv2;

import android.annotation.TargetApi;
import android.content.SharedPreferences;
import android.content.SharedPreferences.OnSharedPreferenceChangeListener;
import android.os.Bundle;
import android.preference.ListPreference;
import android.preference.Preference;
import android.preference.Preference.OnPreferenceChangeListener;
import android.preference.PreferenceActivity;
import android.preference.PreferenceFragment;
import android.preference.PreferenceManager;
import android.view.View;
import android.widget.ImageButton;

public class MyPrefsActivity extends PreferenceActivity implements OnSharedPreferenceChangeListener
{
    private static int prefs = R.xml.settings;
    private ImageButton cbButton, spinnerButton, popupButton;
    private final String LIST_PREFERENCE = "prefCheckboxOption";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        try{
            getClass().getMethod("getFragmentManager");
            AddResourceApi11AndGreater();
        }
        catch(NoSuchMethodException e){ // Android API < 11
            AddResourceApiLessThan11();
        }

        SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this);
        preferences.registerOnSharedPreferenceChangeListener(this);
*       ListPreference listPreference = (ListPreference) findPreference(LIST_PREFERENCE);
        if(listPreference.getValue() == null)
            listPreference.setValue("0");

        cbButton = (ImageButton) MainActivity.mActivity.findViewById(R.id.ibtnCheckbox);
        spinnerButton = (ImageButton) MainActivity.mActivity.findViewById(R.id.ibtnSpinner);
        popupButton = (ImageButton) MainActivity.mActivity.findViewById(R.id.ibtnPopup);

        setChosenPreference(0);
    }

    private void setChosenPreference(int chosen_value){
        // First put all Visibilities on GONE
        cbButton.setVisibility(View.GONE);
        spinnerButton.setVisibility(View.GONE);
        popupButton.setVisibility(View.GONE);

        // Then turn the chosen on VISIBLE again
        switch(chosen_value){
            case 0: // Multi-Click CheckBox
            default:
                cbButton.setVisibility(View.VISIBLE);
                break;
            case 1: // Dropdown CheckBox
                spinnerButton.setVisibility(View.VISIBLE);
                break;
            case 2: // Pop-up CheckBox
                popupButton.setVisibility(View.VISIBLE);
                break;          
        }
    }

    @Override
    public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
        if(key.equals(LIST_PREFERENCE)){
            ListPreference listPreference = (ListPreference) findPreference(key); // LIST_PREFERENCE
            listPreference.setOnPreferenceChangeListener(new OnPreferenceChangeListener() {
                @Override
                public boolean onPreferenceChange(Preference preference, Object newValue) {
                    int chosen_option = Integer.valueOf((String) newValue);
                    setChosenPreference(chosen_option);
                    return false;
                }
            });
        }
        else{
            // Other settings
        }
    }

    @SuppressWarnings("deprecation")
    protected void AddResourceApiLessThan11(){
        addPreferencesFromResource(prefs);
    }

    @TargetApi(11)
    protected void AddResourceApi11AndGreater(){
*       MyPreferenceFragment pf = new MyPreferenceFragment();
        getFragmentManager().beginTransaction().replace(android.R.id.content, pf).commit();
    }

    @TargetApi(11)
    public static class MyPreferenceFragment extends PreferenceFragment{
        @Override
        public void onCreate(Bundle savedInstanceState){
            super.onCreate(savedInstanceState);
*           addPreferencesFromResource(MyPrefsActivity.prefs); // outer class
            // private members seem to be visible for inner class, and
            // making it static made things so much easier
        }
    }
}

还有settings.xml：

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

    <PreferenceCategory android:title="@string/checkbox_options_title" >
        <ListPreference
                android:key="prefCheckboxOption"
                android:title="@string/pref_checkbox_option"
                android:summary="@string/checkbox_options_summary"
                android:entries="@array/checkbox_options"
                android:entryValues="@array/checkbox_option_values" />

    </PreferenceCategory>

</PreferenceScreen>

和arrays.xml：

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string-array name="checkbox_options">
        <item>CheckBox as Multi-Click</item>
        <item>CheckBox as Dropdown</item>
        <item>CheckBox as Pop-up</item>
    </string-array>
    <string-array name="checkbox_option_values">
        <item>0</item>
        <item>1</item>
        <item>2</item>
    </string-array>
</resources>

（当然我还在AndroidManifest.xml中包含了MyPrefsActivity）

我的目标是根据ListPreference中选择的首选项，使三个checkbox-option中的一个（在setChosenPreference方法中找到）可见，另外两个GONE。

现在onCreate（）方法和onSharedPreferenceChanged（）中的Listpreference都为null并给出NullPointerException。所以我设置了一些断点（参见三个“*”），并且它们为null的原因是因为没有调用第三个“*”（在静态类PF中）。

在使用findPreference之前应该调用addPreferencesFromResources，否则它将返回null。有没有人知道为什么在调试过程中我确实得到了AddResourceApi11AndGreater（）方法中的第二个“*”，但是我没有在MyPreferenceFragment类的onCreate方法（）中找到第三个？...没有调用onCreate在所有..

另外，我的其余代码是否正常（-ish）或者我应该更改某些内容以使其按预期工作？

提前感谢您的回复。

TL; DR：MyPreferenceFragment instantion已成功创建，但永远不会调用@Override onCreate方法。

编辑1：好的，我确实发现了问题：当我在活动的onCreate方法中添加addPreferencesFromResource（prefs）作为调试测试时，我发现MyPreferenceFragment类确实正在被初始化，然后它完成了活动的onCreate方法（如果我没有添加addPreferencesFromResource（prefs）测试行，则会在findPreference（）时失败），并且只有在活动的onCreate方法完成后，才会进入MyPreferenceFragment的onCreate方法。

有没有办法让PreferenceFrament的onCreate方法先行，而在活动的onCreate方法中间，所以在AddResourceApi11AndGreater（）之后但是在findPreference（LIST_PREFERENCE）之前？

Answer 1

将您的逻辑移至PF，不要在PreferenceActivity中执行操作。听取偏好变化的方式也有变化。检查代码。

public class MyPrefsActivity extends PreferenceActivity {
    private static int prefs = R.xml.settings;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        try{
            getClass().getMethod("getFragmentManager");
            AddResourceApi11AndGreater();
        }
        catch(NoSuchMethodException e){ // Android API < 11
            AddResourceApiLessThan11();
        }
    }

    @SuppressWarnings("deprecation")
    protected void AddResourceApiLessThan11(){
        addPreferencesFromResource(prefs);
    }

    @TargetApi(11)
    protected void AddResourceApi11AndGreater(){
        getFragmentManager().beginTransaction().replace(android.R.id.content,
                new PF()).commit();
    }

    @TargetApi(11)
    public static class PF extends PreferenceFragment implements SharedPreferences.OnSharedPreferenceChangeListener {
        private ImageButton cbButton, spinnerButton, popupButton;
        private final String LIST_PREFERENCE = "prefCheckboxOption";

        @Override
        public void onCreate(final Bundle savedInstanceState){
            super.onCreate(savedInstanceState);
            addPreferencesFromResource(MyPrefsActivity.prefs); // outer class
            // private members seem to be visible for inner class, and
            // making it static made things so much easier

            SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(getActivity());
            preferences.registerOnSharedPreferenceChangeListener(this);
            ListPreference listPreference = (ListPreference) findPreference(LIST_PREFERENCE);
            if(listPreference.getValue() == null)
                listPreference.setValue("0");



            cbButton = (ImageButton) MainActivity.mActivity.findViewById(R.id.ibtnCheckbox);
            spinnerButton = (ImageButton) MainActivity.mActivity.findViewById(R.id.ibtnSpinner);
            popupButton = (ImageButton) MainActivity.mActivity.findViewById(R.id.ibtnPopup);

            setChosenPreference(Integer.valueOf(preferences.getString(LIST_PREFERENCE, "0")));
        }

        @Override
        public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
            int chosen_option = Integer.valueOf(sharedPreferences.getString(key, "0"));
            setChosenPreference(chosen_option);
        }

        private void setChosenPreference(int chosen_value){
            // First put all Visibilities on GONE
            cbButton.setVisibility(View.GONE);
            spinnerButton.setVisibility(View.GONE);
            popupButton.setVisibility(View.GONE);

            // Then turn the chosen on VISIBLE again
            switch(chosen_value){
                case 0: // Multi-Click CheckBox
                default:
                    cbButton.setVisibility(View.VISIBLE);
                    break;
                case 1: // Dropdown CheckBox
                    spinnerButton.setVisibility(View.VISIBLE);
                    break;
                case 2: // Pop-up CheckBox
                    popupButton.setVisibility(View.VISIBLE);
                    break;
            }
        }
    }
}

Android - SharedPreferences ListPreference - 未调用PreferenceFragment onCreate

1 个答案: