我的主活动类包含TextView和设置活动（从Android的Studio模板生成）。
在设置活动中，我已声明了许多设置。主活动上的TextView显示其中一个设置，这是由一个函数创建的，该函数加载所有首选项的当前状态并将其保存在变量上。
如果我在设置活动上更改某些内容，则侦听器将执行该操作，但不会在主活动上更新该值。
我无法使用onResume()方法，因为它也会在应用首次启动时执行。
我尝试发送一个Intent并从侦听器启动主类，但是这会创建一个主类的新实例，并且只允许您更改一个首选项，因为侦听器会触发。
我的主要活动如下：
public class MainActivity extends ActionBarActivity {
private SharedPreferences prefs;
private double _lat;
public void loadPrefs(){
prefs = PreferenceManager.getDefaultSharedPreferences(this);
_lat = Double.parseDouble(prefs.getString("lat", ""));
//updates the iu
TextView helloThere = (TextView) findViewById(R.id.TextView_hello_world);
helloThere.setText(Double.toString(_lat));
}
@Override
protected void onResume() {
super.onResume();
String changes = getIntent().getStringExtra("prefChanged");
if(changes != null)
Log.d("DEBUG!!!!", changes);
else
Log.d("DEBUG!!!!", "No changes!!!!");
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
loadPrefs();
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
if (id == R.id.action_settings) {
// Launch Settings activity
Intent intent = new Intent(this, SettingsActivity.class);
startActivity(intent);
return true;
}
return super.onOptionsItemSelected(item);
}
}
这是设置活动（查看名为onSharedPreferenceChanged的函数）：
public class SettingsActivity extends PreferenceActivity implements SharedPreferences.OnSharedPreferenceChangeListener {
SharedPreferences.OnSharedPreferenceChangeListener listener;
/**
* Determines whether to always show the simplified settings UI, where
* settings are presented in a single list. When false, settings are shown
* as a master/detail two-pane view on tablets. When true, a single pane is
* shown on tablets.
*/
private static final boolean ALWAYS_SIMPLE_PREFS = false;
private SharedPreferences prefs;
@Override
public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
Log.d("DEBUG!!","LISTENER!!");
Intent i = new Intent(this, MainActivity.class);
i.putExtra("prefChanged","Something changed...");
startActivity(i);
}
@Override
protected void onResume() {
super.onResume();
prefs.registerOnSharedPreferenceChangeListener(this);
}
@Override
protected void onPause() {
super.onPause();
prefs.unregisterOnSharedPreferenceChangeListener(this);
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
prefs = PreferenceManager.getDefaultSharedPreferences(this);
}
@Override
protected void onPostCreate(Bundle savedInstanceState) {
super.onPostCreate(savedInstanceState);
setupSimplePreferencesScreen();
}
/**
* Shows the simplified settings UI if the device configuration if the
* device configuration dictates that a simplified, single-pane UI should be
* shown.
*/
private void setupSimplePreferencesScreen() {
if (!isSimplePreferences(this)) {
return;
}
// In the simplified UI, fragments are not used at all and we instead
// use the older PreferenceActivity APIs.
// Add 'general' preferences.
addPreferencesFromResource(R.xml.pref_general);
// Add 'notifications' preferences, and a corresponding header.
PreferenceCategory fakeHeader = new PreferenceCategory(this);
fakeHeader.setTitle(R.string.pref_header_notifications);
getPreferenceScreen().addPreference(fakeHeader);
addPreferencesFromResource(R.xml.pref_notification);
// Add 'data and sync' preferences, and a corresponding header.
//fakeHeader = new PreferenceCategory(this);
//fakeHeader.setTitle(R.string.pref_header_data_sync);
//getPreferenceScreen().addPreference(fakeHeader);
//addPreferencesFromResource(R.xml.pref_data_sync);
// Bind the summaries of EditText/List/Dialog/Ringtone preferences to
// their values. When their values change, their summaries are updated
// to reflect the new value, per the Android Design guidelines.
//bindPreferenceSummaryToValue(findPreference("example_text"));
//bindPreferenceSummaryToValue(findPreference("example_list"));
bindPreferenceSummaryToValue(findPreference("notifications_ringtone"));
//bindPreferenceSummaryToValue(findPreference("sync_frequency"));
}
/**
* {@inheritDoc}
*/
@Override
public boolean onIsMultiPane() {
return isXLargeTablet(this) && !isSimplePreferences(this);
}
/**
* Helper method to determine if the device has an extra-large screen. For
* example, 10" tablets are extra-large.
*/
private static boolean isXLargeTablet(Context context) {
return (context.getResources().getConfiguration().screenLayout
& Configuration.SCREENLAYOUT_SIZE_MASK) >= Configuration.SCREENLAYOUT_SIZE_XLARGE;
}
/**
* Determines whether the simplified settings UI should be shown. This is
* true if this is forced via {@link #ALWAYS_SIMPLE_PREFS}, or the device
* doesn't have newer APIs like {@link PreferenceFragment}, or the device
* doesn't have an extra-large screen. In these cases, a single-pane
* "simplified" settings UI should be shown.
*/
private static boolean isSimplePreferences(Context context) {
return ALWAYS_SIMPLE_PREFS
|| Build.VERSION.SDK_INT < Build.VERSION_CODES.HONEYCOMB
|| !isXLargeTablet(context);
}
/**
* {@inheritDoc}
*/
@Override
@TargetApi(Build.VERSION_CODES.HONEYCOMB)
public void onBuildHeaders(List<Header> target) {
if (!isSimplePreferences(this)) {
loadHeadersFromResource(R.xml.pref_headers, target);
}
}
/**
* A preference value change listener that updates the preference's summary
* to reflect its new value.
*/
private static Preference.OnPreferenceChangeListener sBindPreferenceSummaryToValueListener = new Preference.OnPreferenceChangeListener() {
@Override
public boolean onPreferenceChange(Preference preference, Object value) {
String stringValue = value.toString();
if (preference instanceof ListPreference) {
// For list preferences, look up the correct display value in
// the preference's 'entries' list.
ListPreference listPreference = (ListPreference) preference;
int index = listPreference.findIndexOfValue(stringValue);
// Set the summary to reflect the new value.
preference.setSummary(
index >= 0
? listPreference.getEntries()[index]
: null);
} else if (preference instanceof RingtonePreference) {
// For ringtone preferences, look up the correct display value
// using RingtoneManager.
if (TextUtils.isEmpty(stringValue)) {
// Empty values correspond to 'silent' (no ringtone).
preference.setSummary(R.string.pref_ringtone_silent);
} else {
Ringtone ringtone = RingtoneManager.getRingtone(
preference.getContext(), Uri.parse(stringValue));
if (ringtone == null) {
// Clear the summary if there was a lookup error.
preference.setSummary(null);
} else {
// Set the summary to reflect the new ringtone display
// name.
String name = ringtone.getTitle(preference.getContext());
preference.setSummary(name);
}
}
} else {
// For all other preferences, set the summary to the value's
// simple string representation.
preference.setSummary(stringValue);
}
return true;
}
};
/**
* Binds a preference's summary to its value. More specifically, when the
* preference's value is changed, its summary (line of text below the
* preference title) is updated to reflect the value. The summary is also
* immediately updated upon calling this method. The exact display format is
* dependent on the type of preference.
*
* @see #sBindPreferenceSummaryToValueListener
*/
private static void bindPreferenceSummaryToValue(Preference preference) {
// Set the listener to watch for value changes.
preference.setOnPreferenceChangeListener(sBindPreferenceSummaryToValueListener);
// Trigger the listener immediately with the preference's
// current value.
sBindPreferenceSummaryToValueListener.onPreferenceChange(preference,
PreferenceManager
.getDefaultSharedPreferences(preference.getContext())
.getString(preference.getKey(), ""));
}
/**
* This fragment shows general preferences only. It is used when the
* activity is showing a two-pane settings UI.
*/
@TargetApi(Build.VERSION_CODES.HONEYCOMB)
public static class GeneralPreferenceFragment extends PreferenceFragment {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.pref_general);
// Bind the summaries of EditText/List/Dialog/Ringtone preferences
// to their values. When their values change, their summaries are
// updated to reflect the new value, per the Android Design
// guidelines.
//bindPreferenceSummaryToValue(findPreference("fixed_lat_long"));
bindPreferenceSummaryToValue(findPreference("example_text"));
bindPreferenceSummaryToValue(findPreference("example_list"));
}
}
/**
* This fragment shows notification preferences only. It is used when the
* activity is showing a two-pane settings UI.
*/
@TargetApi(Build.VERSION_CODES.HONEYCOMB)
public static class NotificationPreferenceFragment extends PreferenceFragment {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.pref_notification);
// Bind the summaries of EditText/List/Dialog/Ringtone preferences
// to their values. When their values change, their summaries are
// updated to reflect the new value, per the Android Design
// guidelines.
bindPreferenceSummaryToValue(findPreference("notifications_ringtone"));
}
}
}
加分问题：我已经使用Android的Studio模板生成了设置活动，我注意到没有onCreate()方法，这是正常的吗？当我从主要活动中调用startactivity()函数时执行了什么？
谢谢。
PS：也许我已经发布了太多的代码来解决这个问题，对不起，我刚刚开始使用Android，感觉就像一个菜鸟。答案 0 :(得分：1)
您不应该尝试从SettingsActivity更改MainActivity的UI！ MainActivity用户界面的管理应该只能自己完成。
看看Activity Lifecycle。您将看到，当活动将返回到前台时，将调用onResume()的{{1}}方法。所以有两个解决方案：
MainActivity中致电loadPrefs()。你告诉你不能这样做，但我不明白为什么（也许我会错过一些细节）onResume()方法中，仅在检测到更改时调用onResume()。再次：不要试图从另一个类调用loadPrefs()的方法：它在Android世界中是无意义的。
Bonus anwser
MainActivity方法在onCreate()类中声明，因此具有默认行为。如果要修改默认行为（即声明自己的UI组件），可以覆盖它（在添加@Override注释时这样做）。所以默认情况下，没有绝对需要覆盖它。如果不覆盖，将调用默认实现。这是一个OOP基础;）
答案 1 :(得分：0)
loadPrefs()而不是onResume() onCreate()
onCreate()方法。