android自动登陆SharedPreferences

LoginActivity.java
public class LoginActivity extends AppCompatActivity {
private Button login;
private EditText username;
private EditText password;
private SharedPreferences pref;
private SharedPreferences.Editor editor;
private CheckBox remember;
private String usernamevalue;
private String passwordvalue;

@Override
protected void onCreate(final Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_login);
    pref = PreferenceManager.getDefaultSharedPreferences(this);
    username = (EditText) findViewById(R.id.e_username);
    password = (EditText) findViewById(R.id.e_password);
    login = (Button) findViewById(R.id.login);
    remember = (CheckBox) findViewById(R.id.checkbox);
    boolean isremember = pref.getBoolean("remember", false);
    if (isremember) {//若选择了记住密码，则下次登陆直接进入登陆后页面
        remember.setChecked(true);
        Intent intent = new Intent(LoginActivity.this, MainActivity.class);
        startActivity(intent);
        Log.e("LoginActivity", "自动登陆");
    }
    login.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            usernamevalue = username.getText().toString();
            passwordvalue = password.getText().toString();
            if (usernamevalue.equals("admin") && passwordvalue.equals("123456")) {
                editor = pref.edit();
                if (remember.isChecked()) {
                    editor.putBoolean("remember", true);
                    editor.putString("username", usernamevalue);
                    editor.putString("password", passwordvalue);
                } else {
                    editor.clear();
                }
                editor.apply();
                Intent intent = new Intent(LoginActivity.this, MainActivity.class);
                startActivity(intent);
                finish();
            } else {
                Toast.makeText(LoginActivity.this, "username or password is invalid", Toast.LENGTH_SHORT).show();
            }
        }

    });

}

}

acitivity_login.xml

xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context="com.example.period.password.LoginActivity">
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:padding="10dp"
android:layout_marginTop="20dp">
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="UserName"
android:layout_weight="4"
android:gravity="center"
/>
android:id="@+id/e_username"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="2"
android:layout_marginRight="15dp"
/>

android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:padding="10dp">
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Password:"
android:layout_weight="4"
android:gravity="center"/>
android:id="@+id/e_password"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="2"
android:layout_marginRight="15dp"
/>

android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:orientation="horizontal"
android:padding="10dp">
android:id="@+id/checkbox"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
/>
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Remember password"/>

android:id="@+id/login"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Login"
android:layout_gravity="center"/>

MainActivity.java //登陆成功后跳转的页面
public class MainActivity extends AppCompatActivity {

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

}

activity_main.xml
android:layout_width="match_parent"
android:layout_height="match_parent"
android:text="welcome!"/>