android - 无法清除共享首选项

Question

我做了一个简单的登录 Activity ，其中我使用 android sqlite 数据库来存储登录信息，即用户名和密码。当用户在注册 Activity 中单击创建帐户按钮时，他/她将被转移到另一个 Activity ，在那里他们可以看到他们的用户名和密码。在该屏幕中，我需要检查首选项是否明确，然后按钮的文本将根据决定进行更改。

我使用 SharedPreference 在 Activity 之间传递了信息，但是当用户单击注销时我无法删除或清除它。下面是两个 Activity 的代码。

这是我的 SignUp.java

@Override
protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.signup);

    // get Instance  of Database Adapter
    loginDataBaseAdapter=new LoginDataBaseAdapter(this);
    loginDataBaseAdapter=loginDataBaseAdapter.open();

    // Get Refferences of Views
    editTextUserName=(EditText)findViewById(R.id.editTextUserName);
    editTextPassword=(EditText)findViewById(R.id.editTextPassword);
    editTextConfirmPassword=(EditText)findViewById(R.id.editTextConfirmPassword);
    tv=(TextView)findViewById(R.id.textView);

    btnCreateAccount=(Button)findViewById(R.id.buttonCreateAccount);
    btnCreateAccount.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            String userName=editTextUserName.getText().toString();
            String password=editTextPassword.getText().toString();
            String confirmPassword=editTextConfirmPassword.getText().toString();

            // check if any of the fields are vaccant
            if(userName.equals("")||password.equals("")||confirmPassword.equals("")) {
                Toast.makeText(getApplicationContext(), "Field Vaccant", Toast.LENGTH_LONG).show();
                return;
            }
            // check if both password matches
            if(!password.equals(confirmPassword)) {
                Toast.makeText(getApplicationContext(), "Password does not match", Toast.LENGTH_LONG).show();
                return;
            }
            if(password.length()<8) {
                Toast.makeText(getApplicationContext(),"Password must be 8 digits longer",Toast.LENGTH_LONG).show();
            }
            else {
                // Save the Data in Database
                loginDataBaseAdapter.insertEntry(userName, password);
                try {

                    sharedPreferences= PreferenceManager.getDefaultSharedPreferences(getApplicationContext());

                    SharedPreferences.Editor editor = sharedPreferences.edit();
                    editor.putString(Name,userName);
                    editor.putString(Pass,password);
                    editor.commit();

                } catch (NullPointerException e) {
                    e.printStackTrace();
                }

                intent=new Intent(getApplicationContext(),AfterLogin.class);
                startActivity(intent);
                Toast.makeText(getApplicationContext(), "Account Successfully Created ", Toast.LENGTH_LONG).show();
            }
        }
    });
}

@Override
protected void onDestroy() {
    super.onDestroy();
    loginDataBaseAdapter.close();
}

和 AfterLogin.Java

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.afterlogin);

    username=(TextView)findViewById(R.id.Username);
    name=(TextView)findViewById(R.id.Name);
    user=(TextView)findViewById(R.id.User);
    pass=(TextView)findViewById(R.id.Pass);
    sout=(Button)findViewById(R.id.SignOut);

    s= sharedPreferences.getString(Name,"");
    us=sharedPreferences.getString(Pass,"");

    username.setText(s);
    name.setText(s);
    user.setText(s);
    pass.setText(us);

    sout.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            SharedPreferences.Editor editor=sharedPreferences.edit();
            editor.clear();
            editor.commit();

            String n=sharedPreferences.getString(Name,"");

            if (n == null) {
                sout.setText("Signed Out");
            }
        }
    });
}

Answer 1

你检查过的AfterLogin.java

n == null

但将字符串 n 的默认值传递为空

String n=sharedPreferences.getString(Name,""); //EMPTY

改变

if (n==null) {
    sout.setText("Signed Out");
}

到

if (n.isEmpty()) {
    sout.setText("Signed Out");
}