Android：如何從偏好活動類中調用主類的方法？

Question

我有一個帶有TextView和settings活動的主活動類（從Android的Studio模板生成）。

在設置活動中，我已經聲明了許多設置。 主活動上的TextView顯示了此設置之一，這是由一個函數完成的，該函數加載所有首選項的當前狀態並將其保存在變量中。

如果我在settings活動上更改了某些內容，偵聽器將執行，但不會在main活動上更新該值。

我不能使用onResume()方法，因為它在應用程序首次啟動時也會執行。

我嘗試過發送一個Intent並從偵聽器中啟動主類，但這會創建主類的新實例，並且由於偵聽器會觸發，因此只允許您更改一個首選項。

我的主要活動如下：

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);
}

}

這是設置活動（查看名為onSharedPreferenceChanged的函數）：

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"));
    }
}

}

額外的問題：我使用Android的Studio模板生成了設置活動，我注意到沒有onCreate()方法，這正常嗎？ 當我從主活動中調用startactivity()函數時，將執行什么操作？

謝謝。

PS：也許我發布了太多代碼來解決問題，對不起，我剛開始使用Android，感覺像個菜鳥。

Answer 1

您不應該嘗試從SettingsActivity更改MainActivity的UI！ MainActivity的UI的管理只能由自己完成。

看一下活動生命周期 。 您將看到，當Activity返回前台時，將調用MainActivity的onResume()方法。 因此有兩種解決方案：

1. 您可以在onResume()調用loadPrefs() onResume() 。 您告訴您無法做到，但我不明白為什么（也許我錯過了一些細節）
2. 在onResume()方法中，僅當檢測到更改時才調用loadPrefs() 。

再次：不要嘗試從另一個類調用MainActivity的方法：在Android世界中這是MainActivity 。

額外獎勵

onCreate()方法在Activity類中聲明，因此具有默認行為。 如果要修改默認行為（即聲明自己的UI組件），則可以覆蓋它（在添加@Override注釋時這樣做）。 因此，默認情況下，沒有絕對需要覆蓋它。 如果沒有覆蓋，則將調用默認實現。 這是基於OOP的；）

Answer 2

1. 無需從設置活動中開始主要活動
2. 從主要活動的onResume()而不是onCreate()調用loadPrefs() onCreate()
3. 設置活動中有onCreate()方法。