英文:
Why can I use print my API response on a button press but not display it as a widget in Flutter? And how do I fix it?
问题
以下是翻译的部分：
-
在我的Flutter应用程序中，我尝试在initState中调用API，并且成功地以我想要的格式获取了响应。我知道这一点，因为当我尝试在按钮按下时打印变量时，我得到了正确的响应。但是，当我尝试在实际应用程序中显示这个响应，比如通过文本小部件或ListView时，出现了错误。
-
我做了以下操作：
- 在initState方法中调用了我的API，并且成功地获取了响应：
dynamic myArticles = {}; @override void initState() { super.initState(); getTopNews().then((value) { setState(() { myArticles = value; }); }); }- 我有一个按钮，成功显示了我从API中想要的响应：
MaterialButton( child: Text("点击"), onPressed: () { print(myArticles["articles"][0]["description"]); } ) //点击按钮后，按钮会打印出我想要的值。- 我添加了一个文本小部件的代码，它应该显示信息，然后重新加载了应用程序，但出现了错误。
Text(myArticles["articles"][0]["description"]) // 这行代码返回一个错误。步骤3中的错误信息如下：
(NoSuchMethodError: 调用了null上的方法'[]'。 接收者：null 尝试调用：[](0))
为什么我会收到这个错误，我如何解决它？我知道我正确地调用了API，我得到了正确的数据，但当我尝试在应用程序中显示相同的信息时，我会收到错误。
英文:
In my Flutter App, I am trying to call an API in initState and I am able to successfully get a response in the format that I want. I know this because when I try and print the variable on a button press, I get the correct response. However, when I try to display this response in the actual app such as through a text widget or a ListView, I get an error.
Here is what I did:
- I called my API in the initState method and I was able to successfully get my response:
dynamic myArticles = {};
@override
void initState() {
super.initState();
getTopNews().then((value) {
setState(() {
myArticles = value;
});
});
}
- I have a button that successfully displays the response that I want from the API:
MaterialButton(
child: Text("Click"),
onPressed: () {
print(myArticles["articles"][0]["description"]);
}
)
//On clicked, the button prints out the value I want.
- I added the code for a Text widget that is supposed to display the information, and I reloaded the app, but I get an error.
Text(myArticles["articles"][0]["description"])
// This line of code returns an error.
The error that I get from step 3 says this:
(NoSuchMethodError: The method '[]' was called on null.
Receiver: null
Tried calling: [](0))
Why am I getting this error and how can I solve it? I know that I am calling the API correctly and I am getting the correct data back, yet when I try to display the same information in the app I am getting an error.
答案1
得分: 0
因为在第一次构建时，myArticles 是空的，而 myArticles["articles"] 会为 null。
你可以使用 ? 来修复它：
Text(myArticles["articles"]?[0]["description"] ?? "")
英文:
Because at the first time build, myArticles is empty and myArticles["articles"] will be null.
You can fix it with ? :
Text(myArticles["articles"]?[0]["description"] ?? "")
答案2
得分: 0
你可以在执行onPress后调用你的API并重新渲染你的小部件树。这将有助于获取响应并更新用户界面。
MaterialButton(
child: Text("点击"),
onPressed: () {
getTopNews().then((value) {
setState(() {
myArticles = value;
});
}
)
英文:
One thing you can do is once you do onPress you can call your API and re-render your widget tree. This will help you to get response and update the UI.
MaterialButton(
child: Text("Click"),
onPressed: () {
getTopNews().then((value) {
setState(() {
myArticles = value;
});
}
)
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