Java Android SwipeRefreshLayout返回null

我想使用SwipeRefreshLayout替换数据， 但当我这么做的时候

mSwipeRefreshLayout = (SwipeRefreshLayout)findViewById(R.id.refresh);

mSwipeRefreshLayout具有null。 代码示例：

<androidx.cardview.widget.CardView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_margin="5dp">
 <androidx.cardview.widget.CardView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_margin="5dp">

<LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_margin="10dp"
            android:orientation="vertical">

  </LinearLayout>

    </androidx.cardview.widget.CardView>
</androidx.swiperefreshlayout.widget.SwipeRefreshLayout>


import androidx.swiperefreshlayout.widget.SwipeRefreshLayout;


private SwipeRefreshLayout mSwipeRefreshLayout ;

@Override
    protected void onCreate(Bundle savedInstanceState) {
        mSwipeRefreshLayout = (SwipeRefreshLayout)findViewById(R.id.refresh);
        mSwipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
            @Override
            public void onRefresh() {
                Toast.makeText(SpisokActivity.this, "Обновление", Toast.LENGTH_SHORT).show();
                mSwipeRefreshLayout.setRefreshing(false);
            }
        });

导入androidx.swiperefreshlayout.widget.swiperefreshlayout；
私人SwipeRefreshLayout mSwipeRefreshLayout；
@凌驾
创建时受保护的void（Bundle savedInstanceState）{
mSwipeRefreshLayout=（SwipeRefreshLayout）findViewById（R.id.refresh）；
mSwipeRefreshLayout.setOnRefreshListener（新的SwipeRefreshLayout.OnRefreshListener（））{
@凌驾
公共void onRefresh（）{
Toast.makeText（SpisokActivity.this，“бббббббббббббб；
mSwipeRefreshLayout.setRefresh（false）；
}
});

那么，在

---

mSwipeRefreshLayout=（SwipeRefreshLayout）findViewById（R.id.refresh）

我收到一个错误。我认为原因是mSwipeRefreshLayout为null。

在

findViewById

setContentView(R.layout.main)

---

谢谢。错误是因为我写的setContentView布局不规则。