兩次按返回按鈕可退出應用，弄亂Android中的視圖

Question

我有MainActivity，它檢查用戶是否使用sessionmanager登錄。 如果未登錄，則將它們定向到LoginActivity.java

但是，當出現登錄屏幕並且用戶按下一次時，我將獲得一個沒有元素的視圖，並且當用戶再次按下時，應用程序將退出。 我想避免應用程序顯示此中間屏幕。

這是MainActivity.java

 public class MainActivity extends Activity {

    // Alert Dialog Manager
    AlertDialogManager alert = new AlertDialogManager();

    // Session Manager Class
    SessionManager session;

    // Button Logout
    Button btnLogout;
    public boolean doubleBackToExitPressedOnce;

    @Override
    public void onBackPressed() {
        if (doubleBackToExitPressedOnce) {
            super.onBackPressed();
            return;
        }

        this.doubleBackToExitPressedOnce = true;
        Toast.makeText(this, "Click Back again to exit", Toast.LENGTH_SHORT).show();

        new Handler().postDelayed(new Runnable() {

            @Override
            public void run() {
                doubleBackToExitPressedOnce=false;
            }
        }, 2000);
    }
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);


        // Session class instance
        session = new SessionManager(getApplicationContext());

        if (session.isLoggedIn()){

            setContentView(R.layout.activity_main);

            TextView lblName = (TextView) findViewById(R.id.lblName);
            TextView lblEmail = (TextView) findViewById(R.id.lblEmail);

            // Button logout
            btnLogout = (Button) findViewById(R.id.btnLogout);

            Toast.makeText(getApplicationContext(), "User Login Status: " + session.isLoggedIn(), Toast.LENGTH_LONG).show();

            // get user data from session
            HashMap user = session.getUserDetails();

            // name
            String name = user.get(SessionManager.KEY_NAME);

            // email
            String email = user.get(SessionManager.KEY_EMAIL);

            // displaying user data
            lblName.setText(Html.fromHtml("Name: " + name + ""));
            lblEmail.setText(Html.fromHtml("Email: " + email + ""));

            btnLogout.setOnClickListener(new View.OnClickListener() {

                @Override
                public void onClick(View arg0) {
                    // Clear the session data
                    // This will clear all session data and
                    // redirect user to LoginActivity
                    session.logoutUser();
                }
            });
        }
        else{

            session.checkLogin();
        }


    }

} 

這是LoginActivity.java

public class LoginActivity extends Activity {

    // Email, password edittext
    EditText txtUsername, txtPassword;

    // login button
    Button btnLogin;

    // Alert Dialog Manager
    AlertDialogManager alert = new AlertDialogManager();

    // Session Manager Class
    SessionManager session;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);

        // Session Manager
        session = new SessionManager(getApplicationContext());

        // Email, Password input text
        txtUsername = (EditText) findViewById(R.id.txtUsername);
        txtPassword = (EditText) findViewById(R.id.txtPassword);

        Toast.makeText(getApplicationContext(), "User Login Status: " + session.isLoggedIn(), Toast.LENGTH_LONG).show();


        // Login button
        btnLogin = (Button) findViewById(R.id.btnLogin);
        Button btnRegister = (Button) findViewById(R.id.btnRegister);

        btnRegister.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent i = new Intent(getApplicationContext(), Register.class);
                startActivity(i);
                finish();
            }
        });

        // Login button click event
        btnLogin.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // Get username, password from EditText
                String username = txtUsername.getText().toString();
                String password = txtPassword.getText().toString();

                // Check if username, password is filled
                if(username.trim().length() > 0 && password.trim().length() > 0){
                    // For testing puspose username, password is checked with sample data
                    // username = test
                    // password = test
                    if(username.equals("test") && password.equals("test")){

                        // Creating user login session
                        // For testing i am stroing name, email as follow
                        // Use user real data
                        session.createLoginSession("Android Hive", "anroidhive@gmail.com");

                        // Staring MainActivity
                        Intent i = new Intent(getApplicationContext(), MainActivity.class);
                        startActivity(i);
                        finish();

                    }else{
                        // username / password doesn't match
                        alert.showAlertDialog(LoginActivity.this, "Login failed..", "Username/Password is incorrect", false);
                    }
                }else{
                    // user didn't entered username or password
                    // Show alert asking him to enter the details
                    alert.showAlertDialog(LoginActivity.this, "Login failed..", "Please enter username and password", false);
                }

            }
        });
    }
} 

這是SessionManager.java

public class SessionManager {
// Shared Preferences
SharedPreferences pref;

// Editor for Shared preferences
Editor editor;

// Context
Context _context;

// Shared pref mode
int PRIVATE_MODE = 0;

// Sharedpref file name
private static final String PREF_NAME = "AndroidHivePref";

// All Shared Preferences Keys
private static final String IS_LOGIN = "IsLoggedIn";

// User name (make variable public to access from outside)
public static final String KEY_NAME = "name";

// Email address (make variable public to access from outside)
public static final String KEY_EMAIL = "email";

// Constructor
public SessionManager(Context context){
    this._context = context;
    pref = _context.getSharedPreferences(PREF_NAME, PRIVATE_MODE);
    editor = pref.edit();
}

/**
 * Create login session
 * */
public void createLoginSession(String name, String email){
    // Storing login value as TRUE
    editor.putBoolean(IS_LOGIN, true);

    // Storing name in pref
    editor.putString(KEY_NAME, name);

    // Storing email in pref
    editor.putString(KEY_EMAIL, email);

    // commit changes
    editor.commit();
}

public void checkLogin(){
    // Check login status
    if(!this.isLoggedIn()){
        // user is not logged in redirect him to Login Activity
        Intent i = new Intent(_context, LoginActivity.class);
        // Closing all the Activities
        i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);

        // Add new Flag to start new Activity
        i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);

        // Staring Login Activity
        _context.startActivity(i);
    }

}


public HashMap<String, String> getUserDetails(){
    HashMap<String, String> user = new HashMap<String, String>();
    // user name
    user.put(KEY_NAME, pref.getString(KEY_NAME, null));

    // user email id
    user.put(KEY_EMAIL, pref.getString(KEY_EMAIL, null));

    // return user
    return user;
}

/**
 * Clear session details
 * */
public void logoutUser(){
    // Clearing all data from Shared Preferences
    editor.clear();
    editor.commit();

    // After logout redirect user to Loing Activity
    Intent i = new Intent(_context, LoginActivity.class);
    // Closing all the Activities
    i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);

    // Add new Flag to start new Activity
    i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);

    // Staring Login Activity
    _context.startActivity(i);
}

/**
 * Quick check for login
 * **/
// Get Login State
public boolean isLoggedIn(){
    return pref.getBoolean(IS_LOGIN, false);
}
}

Answer 1

  private static int  doubleBackToExitPressedOnce = 0;

@Override
    public void onBackPressed() {
        this.doubleBackToExitPressedOnce++;
        if (doubleBackToExitPressedOnce == 2) {
             doubleBackToExitPressedOnce =0;
            super.onBackPressed();
            return;
        }


        Toast.makeText(this, "Click Back again to exit", Toast.LENGTH_SHORT).show();
    }

Answer 2

我通過將以下代碼添加到MainActivity.java解決了這一問題。 但是現在我面臨着另一個問題。 登錄和注銷時，我進入LoginActivity.java 。 現在，如果我按后退按鈕，則可以看到在用戶登錄時顯示信息的活動。這不會發生，因為當用戶單擊注銷時，我正在刪除首選項文件。

 if (!session.isLoggedIn()){
        Intent i = new Intent(getApplicationContext(), LoginActivity.class);
        i.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        startActivity(i);
        finish();
    }