如何在共享首选项中存储默认值

Question

我正在创建一个餐厅应用程序，该应用程序由注册/登录系统的会员和非会员组成，通过跳过注册/登录过程来查看菜单。 我的主屏幕有菜单(供非会员直接查看(、登录和注册按钮(供会员注册/登录(。 我想将默认的 phoneId 和密码存储到 SharedPpreferences，让"非会员"通过跳过登录/注册过程来查看菜单(p/s自动登录仅适用于非会员(。但是，我总是面临nullPointerException错误，并且在非成员按下菜单按钮时无法查看。我不知道哪里出了问题，因为我只是一个初学者和学习过程。

常数.java

public class Constant {
public static final String DEFAULT_PHONE_ID = "9876543210";
public static final String DEFAULT_PASSWORD = "12345";
}

应用首选项.java

public class AppPreferences {
// Class variables
private Context context;
private static SharedPreferences sharedPreferences;
private static SharedPreferences.Editor editor;
public static final String PREF_NAME = "iMenuApp";
private int PRIVATE_MODE = 0;
// Define your preferences key
private static final String USER_PHONE = "9876543210";
private static final String USER_PASSWORD = "12345";
private AppPreferences(Context context)
{
this.context = context;
sharedPreferences = this.context.getSharedPreferences(PREF_NAME, PRIVATE_MODE);
if (sharedPreferences != null)
{
editor = sharedPreferences.edit();
}
}
//Store user PhoneId

public void setUserPhoneId(String userId){
String TAG = "AppPref:setUserId";
try
{
editor.putString(USER_PHONE, userId);
editor.commit();
} catch (Exception e) {
Log.e(TAG, String.valueOf(e));
}
}
// Get userPhoneId
public String getUserPhoneId(){
return sharedPreferences.getString(USER_PHONE,"default_phone");
}
//Store userPassword
public void setUserPassword(String userPassword){
String TAG = "AppPref:setUserPassword";
try
{
editor.putString(USER_PASSWORD, userPassword);
editor.commit();
} catch (Exception e) {
Log.e(TAG, String.valueOf(e));
}
}
// Get userPassword
public String getUserPassword(){
return sharedPreferences.getString(USER_PASSWORD,"default_password");
}

}

主要活动.java

public class MainActivity extends AppCompatActivity {
Button btnSignIn, btnSignUp, btnMenu;
public AppPreferences appPreference;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btnMenu = (Button)findViewById(R.id.btnMenu);
btnSignUp = (Button)findViewById(R.id.btnSignUp);
btnSignIn = (Button)findViewById(R.id.btnSignIn);

btnMenu.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent home = new Intent(MainActivity.this, Home.class);
//Here save user info to preferences
appPreference.setUserPhoneId(Constant.DEFAULT_PHONE_ID);
appPreference.setUserPassword(Constant.DEFAULT_PASSWORD);
startActivity(home);

}
});
btnSignUp.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent signUp = new Intent(MainActivity.this, SignUp.class);
startActivity(signUp);
}
});
btnSignIn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent signIn = new Intent(MainActivity.this, SignIn.class);
startActivity(signIn);
}
});
}
}

我需要跟踪非会员的交易订单，所以我需要在默认的 phoneId 和密码下设置所有非会员。

Answer 1

您从未在 MainActivity 中初始化过appPreference。

在onCreate()下执行此操作：

appPreference = new AppPreferences(this);

Answer 2

您需要先初始化应用程序首选项对象，然后才能访问其方法和默认值，如果未找到键值，则可以从首选项返回。

sharedPreferences.getString(USER_PHONE,"default_phone");