角形材料扩展面板，带有子扩展面板

实际上我已经使用角度材料扩展面板（手风琴）进行面板扩展 . 所以我试过的是我只想在一个父扩展面板中显示这样的子面板 . 见下图 .

数据库将成为顶级父级面板，在其中我有不同的数据库作为子面板 . 为此，我写了这样的代码 . 但是，当我点击子面板内的任何父面板时，代码不起作用，然后一切都崩溃了 . 我的意思是说面板正在倒塌 . 见下面的代码：

<mat-accordion>

        <mat-expansion-panel>
            <mat-expansion-panel-header>
              <mat-panel-title>
                Databases
              </mat-panel-title>
              </mat-expansion-panel-header>


              <mat-expansion-panel (opened)="panelOpenState = true"
                             (closed)="panelOpenState = false">
                  <mat-expansion-panel-header>
                    <mat-panel-title>
                      MySQL
                    </mat-panel-title>
                  </mat-expansion-panel-header>

                  <mat-form-field>
                    <textarea matInput placeholder="Assertions"></textarea>
                  </mat-form-field>

                  <mat-form-field>
                      <textarea matInput placeholder="Assertions"></textarea>
                    </mat-form-field>

                    <mat-form-field>
                        <textarea matInput placeholder="Assertions"></textarea>
                      </mat-form-field>

                      <mat-form-field>
                          <textarea matInput placeholder="Assertions"></textarea>
                        </mat-form-field>
                </mat-expansion-panel>


                <mat-expansion-panel (opened)="panelOpenState = true"
                             (closed)="panelOpenState = false">
                  <mat-expansion-panel-header>
                    <mat-panel-title>
                        Oracle
                    </mat-panel-title>
                  </mat-expansion-panel-header>

                  <mat-form-field>
                    <textarea matInput placeholder="Assertions"></textarea>
                  </mat-form-field>

                  <mat-form-field>
                      <textarea matInput placeholder="Assertions"></textarea>
                    </mat-form-field>

                    <mat-form-field>
                        <textarea matInput placeholder="Assertions"></textarea>
                      </mat-form-field>

                      <mat-form-field>
                          <textarea matInput placeholder="Assertions"></textarea>
                        </mat-form-field>
                </mat-expansion-panel>

                <mat-expansion-panel (opened)="panelOpenState = true"
                             (closed)="panelOpenState = false">
                  <mat-expansion-panel-header>
                    <mat-panel-title>
                        Postgres
                    </mat-panel-title>
                  </mat-expansion-panel-header>

                  <mat-form-field>
                    <textarea matInput placeholder="Assertions"></textarea>
                  </mat-form-field>

                  <mat-form-field>
                      <textarea matInput placeholder="Assertions"></textarea>
                    </mat-form-field>

                    <mat-form-field>
                        <textarea matInput placeholder="Assertions"></textarea>
                      </mat-form-field>

                      <mat-form-field>
                          <textarea matInput placeholder="Assertions"></textarea>
                        </mat-form-field>
                </mat-expansion-panel>

                <mat-expansion-panel (opened)="panelOpenState = true"
                             (closed)="panelOpenState = false">
                  <mat-expansion-panel-header>
                    <mat-panel-title>
                        SQLServer
                    </mat-panel-title>
                  </mat-expansion-panel-header>

                  <mat-form-field>
                    <textarea matInput placeholder="Assertions"></textarea>
                  </mat-form-field>

                  <mat-form-field>
                      <textarea matInput placeholder="Assertions"></textarea>
                    </mat-form-field>

                    <mat-form-field>
                        <textarea matInput placeholder="Assertions"></textarea>
                      </mat-form-field>

                      <mat-form-field>
                          <textarea matInput placeholder="Assertions"></textarea>
                        </mat-form-field>
                </mat-expansion-panel>

                <mat-expansion-panel (opened)="panelOpenState = true"
                             (closed)="panelOpenState = false">
                  <mat-expansion-panel-header>
                    <mat-panel-title>
                        MongoDB
                    </mat-panel-title>
                  </mat-expansion-panel-header>

                  <mat-form-field>
                    <textarea matInput placeholder="Assertions"></textarea>
                  </mat-form-field>

                  <mat-form-field>
                      <textarea matInput placeholder="Assertions"></textarea>
                    </mat-form-field>

                    <mat-form-field>
                        <textarea matInput placeholder="Assertions"></textarea>
                      </mat-form-field>

                      <mat-form-field>
                          <textarea matInput placeholder="Assertions"></textarea>
                        </mat-form-field>
                </mat-expansion-panel>

          </mat-expansion-panel>
</mat-accordion>

我的计划是仅显示该特定面板 . 这很奇怪它不适合我 . 如果我将扩展面板放在单独的面板中，那么就为我工作 . 谁能建议我？