如何在OnBackPressed上显示自定义对话框

// custom_dialog.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="确定要退出吗？"
        android:textSize="18sp"
        android:padding="16dp" />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <Button
            android:id="@+id/btn_cancel"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="取消" />

        <Button
            android:id="@+id/btn_confirm"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="确定" />

    </LinearLayout>
</LinearLayout>

// CustomDialog.java
public class CustomDialog extends Dialog implements View.OnClickListener {
    private Button btnCancel;
    private Button btnConfirm;

    public CustomDialog(Context context) {
        super(context);
    }

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

        btnCancel = findViewById(R.id.btn_cancel);
        btnConfirm = findViewById(R.id.btn_confirm);

        btnCancel.setOnClickListener(this);
        btnConfirm.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.btn_cancel:
                dismiss();
                break;
            case R.id.btn_confirm:
                // 执行相应操作，例如关闭当前Activity
                finish();
                break;
        }
    }
}

// MainActivity.java
public class MainActivity extends AppCompatActivity {
    private CustomDialog customDialog;

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

    @Override
    public void onBackPressed() {
        customDialog = new CustomDialog(this);
        customDialog.show();
    }
}