Android stdio 用代码实现，用户注册账号密码登陆。其中布局文件已经给出有两个EditText和两个Button和一个CheckBox组成。要求注册账号密码时，如果当前账号密码没有注册过则可以注册成功，否则注册失败。 登陆账号密码时会和注册的账号密码比对，如果相同则登陆成功，否则登陆失败。 CheckBox如果被赋予true，则下次打开软件时自动填充账号密码。 最终将代码以一个xml和一个Activity的格式给出

下面是实现该功能的代码：

activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="@dimen/activity_horizontal_margin"
    tools:context=".MainActivity">

    <EditText
        android:id="@+id/et_username"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="@string/username"/>

    <EditText
        android:id="@+id/et_password"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/et_username"
        android:hint="@string/password"
        android:inputType="textPassword"/>

    <Button
        android:id="@+id/btn_register"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/et_password"
        android:layout_alignParentStart="true"
        android:text="@string/register"/>

    <Button
        android:id="@+id/btn_login"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/et_password"
        android:layout_alignParentEnd="true"
        android:text="@string/login"/>

    <CheckBox
        android:id="@+id/cb_remember"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/btn_register"
        android:text="@string/remember"/>

</RelativeLayout>

MainActivity.java:

import android.content.Context;
import android.content.SharedPreferences;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    private EditText et_username;
    private EditText et_password;
    private Button btn_register;
    private Button btn_login;
    private CheckBox cb_remember;
    private SharedPreferences sp;

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

        et_username = (EditText) findViewById(R.id.et_username);
        et_password = (EditText) findViewById(R.id.et_password);
        btn_register = (Button) findViewById(R.id.btn_register);
        btn_login = (Button) findViewById(R.id.btn_login);
        cb_remember = (CheckBox) findViewById(R.id.cb_remember);
        sp = getSharedPreferences("user", Context.MODE_PRIVATE);

        btn_register.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String username = et_username.getText().toString();
                String password = et_password.getText().toString();
                if (username.isEmpty() || password.isEmpty()) {
                    Toast.makeText(MainActivity.this, R.string.empty_input, Toast.LENGTH_SHORT).show();
                } else {
                    if (sp.contains(username)) {
                        Toast.makeText(MainActivity.this, R.string.username_exist, Toast.LENGTH_SHORT).show();
                    } else {
                        sp.edit().putString(username, password).apply();
                        Toast.makeText(MainActivity.this, R.string.register_success, Toast.LENGTH_SHORT).show();
                    }
                }
            }
        });

        btn_login.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String username = et_username.getText().toString();
                String password = et_password.getText().toString();
                if (username.isEmpty() || password.isEmpty()) {
                    Toast.makeText(MainActivity.this, R.string.empty_input, Toast.LENGTH_SHORT).show();
                } else {
                    if (sp.contains(username)) {
                        if (password.equals(sp.getString(username, ""))) {
                            Toast.makeText(MainActivity.this, R.string.login_success, Toast.LENGTH_SHORT).show();
                            if (cb_remember.isChecked()) {
                                sp.edit().putString("last_user", username).apply();
                            }
                        } else {
                            Toast.makeText(MainActivity.this, R.string.password_error, Toast.LENGTH_SHORT).show();
                        }
                    } else {
                        Toast.makeText(MainActivity.this, R.string.username_not_exist, Toast.LENGTH_SHORT).show();
                    }
                }
            }
        });

        String lastUser = sp.getString("last_user", "");
        if (!lastUser.isEmpty()) {
            et_username.setText(lastUser);
            et_password.setText(sp.getString(lastUser, ""));
            cb_remember.setChecked(true);
        }
    }
}

strings.xml:

<resources>
    <string name="app_name">UserLogin</string>
    <string name="username">Username</string>
    <string name="password">Password</string>
    <string name="register">Register</string>
    <string name="login">Login</string>
    <string name="remember">Remember me</string>
    <string name="empty_input">Username or password cannot be empty</string>
    <string name="username_exist">Username already exists</string>
    <string name="register_success">Register successful</string>
    <string name="login_success">Login successful</string>
    <string name="password_error">Password incorrect</string>
    <string name="username_not_exist">Username not exist</string>
</resources>