Java 非活动类或RecyclerView适配器类中的SharedReference

我已将SharedReferences保存在设置活动上，并能够在加载时获取它。我还能够在主活动中获取相同的共享首选项。然而，当我试图在一个单独的类上调用它时，我打算在recyclerview适配器上使用它，就像每个card视图元素中的前缀一样，我得到一个空错误。以下是挑战：

我在建立正确的环境方面面临困难

我尝试在首选项类/活动中创建一个getter 从单独的java类调用时返回null

我尝试在适配器类中定义一个上下文，并按如下方式使用它

---

也尝试过：

sharedPreferences=PreferenceManager.getDefaultSharedPreferences(context.getApplicationContext()); 

调用此SharedReference行时出现以下错误

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference

你能帮我怎么做吗 或者设置一个我可以从单独的类调用的getter， 或者直接初始化并获取这个单独类中的值

主要活动 公共类MainActivity扩展了AppCompatActivity{

Button btnm, btnw, btnsep;
Intent intent;
TextView tvRecall;
Third third;
Shared shared;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    btnm = findViewById(R.id.btnmain);
    btnw = findViewById(R.id.btnwhat);
    btnsep = findViewById(R.id.sepClass);
    tvRecall=findViewById(R.id.txtRecall);

    intent = new Intent(this, Shared.class);

    btnm.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            startActivity(intent);

        }
    });


    btnw.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

           SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
            String s = sharedPreferences.getString("txt","");
            Log.i("testlog*****","t "+ s);
            Toast.makeText(getApplicationContext(),"Text is " + s,Toast.LENGTH_SHORT).show();

        }
    });

    btnsep.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
           third = new Third();
           third.callSharedPreference();
        }
    });

}

EditText textView ;
Button btn;
SharedPreferences sharedPreferences;
Context c;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_shared);
    textView = findViewById(R.id.txtName);
    btn = findViewById(R.id.btnName);



    btn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            sharedPreferences = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
            sharedPreferences.edit().putString("txt",textView.getText().toString()).apply();
        }
    });


}

public Shared () {    }

public void getlog () {
        sharedPreferences = PreferenceManager.getDefaultSharedPreferences(c);
        String s = sharedPreferences.getString("txt","");
        Log.i("testlog*****","t "+ s);
        Toast.makeText(getApplicationContext(),"Text is " + s,Toast.LENGTH_SHORT).show();
}

保存共享pref的活动 公共类共享扩展AppCompatActivity{

Button btnm, btnw, btnsep;
Intent intent;
TextView tvRecall;
Third third;
Shared shared;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    btnm = findViewById(R.id.btnmain);
    btnw = findViewById(R.id.btnwhat);
    btnsep = findViewById(R.id.sepClass);
    tvRecall=findViewById(R.id.txtRecall);

    intent = new Intent(this, Shared.class);

    btnm.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            startActivity(intent);

        }
    });


    btnw.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

           SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
            String s = sharedPreferences.getString("txt","");
            Log.i("testlog*****","t "+ s);
            Toast.makeText(getApplicationContext(),"Text is " + s,Toast.LENGTH_SHORT).show();

        }
    });

    btnsep.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
           third = new Third();
           third.callSharedPreference();
        }
    });

}

EditText textView ;
Button btn;
SharedPreferences sharedPreferences;
Context c;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_shared);
    textView = findViewById(R.id.txtName);
    btn = findViewById(R.id.btnName);



    btn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            sharedPreferences = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
            sharedPreferences.edit().putString("txt",textView.getText().toString()).apply();
        }
    });


}

public Shared () {    }

public void getlog () {
        sharedPreferences = PreferenceManager.getDefaultSharedPreferences(c);
        String s = sharedPreferences.getString("txt","");
        Log.i("testlog*****","t "+ s);
        Toast.makeText(getApplicationContext(),"Text is " + s,Toast.LENGTH_SHORT).show();
}

调用SharedReference的第三个类，调用时会出现如上所述的null错误 公共三等舱{

Context context;
SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(context.getApplicationContext());
String s = sharedPreferences.getString("txt","");


public Third (){}

public void callSharedPreference () {

    Log.i("testlog*****","t "+ s);
    Toast.makeText(context.getApplicationContext(),"Text is ==== " + s,Toast.LENGTH_SHORT).show();

}

---

在第三个类中，上下文未初始化 因此，您应该在构造函数方法中初始化它，并在调用该类时将值传递给它。。。 像这样

public class Third {
Context context;
SharedPreferences sharedPreferences = 
PreferenceManager.getDefaultSharedPreferences(context.getApplicationContext());
String s = sharedPreferences.getString("txt","");


public Third (Context context){
    this.context=context
}
//...
}

---

context

对象是什么？请发布整个代码。欢迎使用SO salman。您是否尝试过：

GetDefaultSharedReferences（context）；

只有一个

context

？请在您的问题中添加这些代码日志，不要将其作为注释发送。（使用编辑按钮）不过，也请在这里查看我的答案：嗨，流浪者。我终于找到了发布代码的方法。刚刚编辑了我的问题。嗨，莫森，谢谢。刚刚更新以提供代码的完整视图。谢谢莫森的帮助。我是用你的参考资料找到的。似乎我传递了错误的上下文。我仍然在想如何标记代码斯蒂恩回答了你的评论。