列的子项不得包含任何空值，但在索引 0 处发现了空值

Question

我正在开发一个 Flutter 应用程序，我正在尝试创建一个 InAppWebView。在 Android 上一切正常，但在 iOS 上出现错误：

“列的子项不得包含任何空值，但在索引 0 处发现了空值”。

我已经完成了 flutter clean、flutter build ios 和 clean xcode。但是还是报错。

感谢任何帮助

这是我的代码：

child: Scaffold(
        appBar: AppBar(title: Text("voucherweb")),
        body: Container(
            child: Column(children: <Widget>[
              progress == null ? Container() : (progress != 1.0)
              ? LinearProgressIndicator(
                  value: progress,
                  backgroundColor: Colors.grey[200],
                  valueColor: AlwaysStoppedAnimation<Color>(Colors.black))
              : null,
          Expanded(
            child: Container(
              child: InAppWebView(
                  initialUrl: "https://voucherweb.com",
                  initialHeaders: {},
                  initialOptions: InAppWebViewGroupOptions(
                    crossPlatform: InAppWebViewOptions(
                        debuggingEnabled: true,
                        useShouldOverrideUrlLoading: true),
                  ),
                  shouldOverrideUrlLoading: (controller, request) async {
                    var url = request.url;
                    var uri = Uri.parse(url);
                    if (request.url.startsWith("https://wa.me/")) {
                      final newString =
                          url.replaceAll("https://wa.me/", "");
                      if (await canLaunch(url)) {
                        FlutterOpenWhatsapp.sendSingleMessage(
                            newString, "Halo, gan. Mau order voucher : ");
                        return ShouldOverrideUrlLoadingAction.CANCEL;
                      }
                    }
                    return ShouldOverrideUrlLoadingAction.ALLOW;
                  },
                  onWebViewCreated: (InAppWebViewController controller) {
                    webView = controller;
                  },
                  onLoadStart:
                      (InAppWebViewController controller, String url) {},
                  onLoadStop:
                      (InAppWebViewController controller, String url) {},
                  onProgressChanged:
                      (InAppWebViewController controller, int progress) {
                    setState(() {
                      this.progress = progress / 100;
                    });
                  }),
            ),
          ),
        ]))));

Answer 1

您正在将 Column's 子项之一设置为 null，请考虑改用 SizedBox() 或 Container()：

我使用您的代码添加了一个示例：

child: Scaffold(
        appBar: AppBar(title: Text("voucherweb")),
        body: Container(
            child: Column(children: <Widget>[
              progress == null ? Container() : (progress != 1.0)
              ? LinearProgressIndicator(
                  value: progress,
                  backgroundColor: Colors.grey[200],
                  valueColor: AlwaysStoppedAnimation<Color>(Colors.black))
              // new line
              : SizedBox(),
          Expanded(
            child: Container(
              child: InAppWebView(
                  initialUrl: "https://voucherweb.com",
                  initialHeaders: {},
                  initialOptions: InAppWebViewGroupOptions(
                    crossPlatform: InAppWebViewOptions(
                        debuggingEnabled: true,
                        useShouldOverrideUrlLoading: true),
                  ),
                  shouldOverrideUrlLoading: (controller, request) async {
                    var url = request.url;
                    var uri = Uri.parse(url);
                    if (request.url.startsWith("https://wa.me/")) {
                      final newString =
                          url.replaceAll("https://wa.me/", "");
                      if (await canLaunch(url)) {
                        FlutterOpenWhatsapp.sendSingleMessage(
                            newString, "Halo, gan. Mau order voucher : ");
                        return ShouldOverrideUrlLoadingAction.CANCEL;
                      }
                    }
                    return ShouldOverrideUrlLoadingAction.ALLOW;
                  },
                  onWebViewCreated: (InAppWebViewController controller) {
                    webView = controller;
                  },
                  onLoadStart:
                      (InAppWebViewController controller, String url) {},
                  onLoadStop:
                      (InAppWebViewController controller, String url) {},
                  onProgressChanged:
                      (InAppWebViewController controller, int progress) {
                    setState(() {
                      this.progress = progress / 100;
                    });
                  }),
            ),
          ),
        ]))));

Answer 2

progress == null ? Container() : (progress != 1.0)
? LinearProgressIndicator(
value: progress,
backgroundColor: Colors.grey[200],
valueColor: AlwaysStoppedAnimation<Color>(Colors.black))
: Container(),

请使用此代码 null 不是小部件，这就是您收到此错误的原因。

列的子项不得包含任何空值，但在索引 0 处发现了空值

Column's children must not contain any null values, but null value was found at index 0

webview

ios

flutter