昨天，我为我的Android应用程序构建了一个SettingsActivity，用户可以在其中输入webservice-server的URL。我使用以下方法保存：
editor = sharedPref.edit();
editor.putString(
getString(R.string.SAVED_URL_MOBILEHELPER), lvsURL_mobilehelper);
editor.commit();
在按下“保存”按钮后的SharedPreferences中。
在onStart()我读取了设置，将保存的值设置为所属文本字段：
// line 29
String lvsURL_mobilehelper = sharedPref.getString(
getString(R.string.SAVED_URL_MOBILEHELPER), "");
昨天也运作良好;我输入并成功从设置中读取的最后一个字符串是“testURL12345”。
今天，我试图在我的应用程序周围添加用户身份验证，因此，当我打开SettingsActivity时，我得到ClassCastException：
Caused by: java.lang.ClassCastException: java.lang.Long cannot be cast to
java.lang.String
at android.app.SharedPreferencesImpl.getString(SharedPreferencesImpl.java:224)
at de.unibonn.sdb.wissappmobile.activities.SettingsActivity.onResume(
SettingsActivity.java:29)
有没有人知道为什么昨天一切正常，现在却没有？
注意：我不希望将用户凭据存储在AccountManager或我的偏好设置中，因为该应用程序应在“商务平板电脑”上使用，而不是“个人平板电脑”。 HTTP-Basic身份验证需要用户凭据。所以我的想法是检查父Activity是否用户“登录”并且不活动超过1800秒。
/*
* Activity for settings page (webservice URL)
*/
public class SettingsActivity extends AppFragmentActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_settings);
}
@Override
protected void onResume() {
super.onResume();
// Fill content
// URL of the Mobile Helper
String lvsURL_mobilehelper = sharedPref.getString(
getString(R.string.SAVED_URL_MOBILEHELPER), "");
EditText dfsURLMobileHelper = (EditText) findViewById(R.id.dfsURLMobileHelper);
dfsURLMobileHelper.setText(lvsURL_mobilehelper);
}
/*
* Action called when pressing the "Save"-Button
*
* Saves the entered Data in a local file.
*/
public void ClickBtnSave(View view) {
EditText dfsURLMobileHelper = (EditText) findViewById(R.id.dfsURLMobileHelper);
TextView txtError = (TextView) findViewById(R.id.txtError);
String lvsURL_mobilehelper = dfsURLMobileHelper.getText().toString();
String Eceptiontext = "";
Boolean success = false;
// Write to file
try {
editor = sharedPref.edit();
editor.putString(getString(R.string.SAVED_URL_MOBILEHELPER), lvsURL_mobilehelper);
editor.commit();
success = true;
} catch (Exception e) {
success = false;
Eceptiontext = e.getLocalizedMessage();
}
if (success) {
txtError.setText(getString(R.string.SAVING_SUCCESS));
} else {
txtError.setText(getString(R.string.SAVING_FAILED) + " : " + Eceptiontext);
}
}
/*
* Action called when pressing the "Back"-Button
*
* Opens the Search-Acitivity
*/
public void ClickBtnBack(View view) {
// Back to SearchActivity
Intent intent = new Intent(this, SearchActivity.class);
startActivity(intent);
}
}
/**
* Class to handle global Callbacks (e.g. user credentials)
*/
public class AppFragmentActivity extends FragmentActivity {
protected SharedPreferences sharedPref;
protected SharedPreferences.Editor editor;
protected String WebServiceUsername;
protected String WebServicePassword;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_appfragmentactivity);
}
@Override
protected void onResume () {
super.onResume();
// Check if user is "logged in".
// Meaning: Are there given user credentials and are they valid of was the user inactive for too long?
// We only do this "onResume" because this callback is the only one, which is called everytime an user
// starts/restarts/resumes an application
checkForUserCredentials();
// Set new "last action" now "now"
setLastAction(new Date().getTime());
}
@Override
protected void onStart () {
// Fill content
super.onStart();
// Set global sharedPreferences
sharedPref = getSharedPreferences(
getString(R.string.FILE_settings_file), Context.MODE_PRIVATE);
}
/*
* Checks if user credentials are valid meaning if they are set and not too old
*/
private void checkForUserCredentials() {
// Get filehandle to PreferencesFile
long TimeLastAction = sharedPref.getLong(
getString(R.string.SETTINGS_USER_LAST_ACTION), 0);
long TimeNow = new Date().getTime();
// Ask for User credentials when last action is too long ago
if(TimeLastAction < (TimeNow - 1800)) {
// Inactive for too long
// Set credentials back
setUsernameAndPassword("", "");
} else {
WebServiceUsername = sharedPref.getString(
getString(R.string.SETTINGS_USER_USERNAME), "");
WebServicePassword = sharedPref.getString(
getString(R.string.SETTINGS_USER_PASSWORD), "");
}
}
/*
* Saves the given last action in the sharedPreferences
* @param long LastAction - Time of the last action
*/
private void setLastAction(long LastAction) {
editor = sharedPref.edit();
editor.putLong(getString(R.string.SETTINGS_USER_LAST_ACTION), LastAction);
editor.commit();
}
/*
* Saves the given username and userpassword sharedPreferences
* @param String username
* @param String password
*/
private void setUsernameAndPassword(String username, String password) {
editor = sharedPref.edit();
editor.putString(
getString(R.string.SETTINGS_USER_USERNAME), username);
editor.putString(
getString(R.string.SETTINGS_USER_PASSWORD), username);
editor.commit();
WebServiceUsername = username;
WebServicePassword = password;
}
/*
* Method called when pressing the OK-Button
*/
public void ClickBtnOK(View view) {
// Save User-Creentials
EditText dfsUsername = (EditText) findViewById(R.id.dfsUsername);
String lvsUsername = dfsUsername.getText().toString();
EditText dfsPassword = (EditText) findViewById(R.id.dfsPassword);
String lvsPassword = dfsPassword.getText().toString();
if(lvsUsername.equals("") || lvsPassword.equals("")) {
TextView txtError = (TextView) findViewById(R.id.txtError);
txtError.setText(getString(R.string.ERR_Name_or_Password_empty));
} else {
// Save credentials
setUsernameAndPassword(lvsUsername, lvsPassword);
setLastAction(new Date().getTime());
// open Searchactivity
Intent intent = new Intent(this, SearchActivity.class);
startActivity(intent);
}
}
@Override
protected void onPause() {
super.onPause();
setLastAction(new Date().getTime());
}
@Override
protected void onStop() {
super.onStop();
setLastAction(0);
setUsernameAndPassword("", "");
}
}
答案 0 :(得分：0)
P.S。我认为最佳做法是使用public static final String MY_PREFERENCE_KEY = "my_preference_key";