共享preferences使应用程序强制关闭 [英] SharedPreferences makes app force close

问题描述

我要读取和写入共享preferences 通过类，但是当我在我的活动调用这个类它使应用程序崩溃/强制关闭

I want to read and write SharedPreferences through a class, but when I call this class in my Activity it makes the app crash/force close

如果在复选框记住电子邮件被选中的应用程序会记住的电子邮件。

If the CheckBox "Remember email" is checked the app will remember the email.

我的 LoginActivity ：

public class LoginActivity extends Activity
{
    private AppPreferences appPreferences;

    @Override
    protected void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);        
        appPreferences = new AppPreferences(); // this makes the app crash
        String email = appPreferences.getPreferenceString("email");
        // ...

类应用preferences

public class AppPreferences extends Activity
{
    private SharedPreferences settings = null;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        settings = this.getSharedPreferences(LOGIN_CREDENTIALS, MODE_PRIVATE);
    }
    public String getPreferenceString(String key) {
        return settings.getString(key, DEFAULT_STRING);
    }
    public void setPreferenceString(String key, String value) {
    editor.putString(key, (String) value);
    }
// ...

我一直在寻找一些时间来解决这个问题，我从这么试了几种解决方案。我称之为 getShared preferences 方法在的onCreate 方法，这样就不会成为问题。

I've been looking for some hours to fix this and I tried several solutions from SO. I do call the getSharedPreferences method in the onCreate method so that wouldn't be the problem.

我是什么做错了吗？我是新来的Java和Android发展得如此充分，请举例说明。一个完整的不同的方法，其他的解决方案也欢迎。先谢谢了。

What am I doing wrong? I'm new to Java and Android developing so please describe fully with examples. Other solutions with a complete different approach are welcome too. Thanks in advance.

推荐答案

由于您要创建一个扩展Activity类类的一个对象。如果应用程序preferences非活动类，那么只传递当前活动上下文相关的分离code在单独的Java类的共享preferences：

because you are trying to create an object of class which extending Activity class. if AppPreferences is non Activity class then just pass current Activity context for separating SharedPreferences related code in separate java class as :

public class AppPreferences  
{
    private SharedPreferences settings = null;
    Context context;
    public AppPreferences(Context context){
     this.context=context;
     settings = context.getSharedPreferences(LOGIN_CREDENTIALS, MODE_PRIVATE);
    }
//your code here....

}

现在通过使用应用preferences 构造为活动背景：

now pass Activity context using AppPreferences constructor as :

appPreferences = new AppPreferences(LoginActivity.this);
String email = appPreferences.getPreferenceString("email");

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