问'.MainActivity' is not an enclosing class？

 public  class MainActivity extends AppCompatActivity {

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

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
    }
}

public class TitleLayout extends LinearLayout {

    public TitleLayout(Context context, AttributeSet attrs) {

        super(context, attrs);
        LayoutInflater.from(context).inflate(R.layout.title, this);

        Button btn_plus = (Button) findViewById(R.id.title_btn);
        Button btn_exit = (Button) findViewById(R.id.title_btn2);

        btn_plus.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(MainActivity.this,new_cost.class));
            }
        });

        btn_exit.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                ((new_cost)getContext()).finish();
            }
        });
    }

}