我有一个我希望在Flutter中作为下拉列表实现的位置列表.我对这门语言很陌生.这就是我所做的.
new DropdownButton(
value: _selectedLocation,
onChanged: (String newValue) {
setState(() {
_selectedLocation = newValue;
});
},
items: _locations.map((String location) {
return new DropdownMenuItem<String>(
child: new Text(location),
);
}).toList(),
这是我的项目清单:
List<String> _locations = ['A', 'B', 'C', 'D'];
我收到以下错误.
Another exception was thrown: 'package:flutter/src/material/dropdown.dart': Failed assertion: line 468 pos 15: 'value == null || items.where((DropdownMenuItem<T> item) => item.value == value).length == 1': is not true.
我假设值为_selectedLocationnull.但我正在初始化它.
String _selectedLocation = 'Please choose a location';
我在运行时收到此错误 pod install
[!] The 'Pods-Runner' target has transitive dependencies that include static binaries: (/Users/me/Documents/flutter/flutter/bin/cache/artifacts/engine/ios/Flutter.framework)
在做了一些研究之后，它说use frameworks!我Podfile的问题是造成这个问题的。如果我注释掉use frameworks!我会收到这个错误。知道问题是什么吗？过去三天我一直被困在这里。
ld: framework not found Flutter
clang: error: linker command failed with exit code 1 (use -v to see invocation)
也根据这里写的内容。添加以下内容Podfile对我也不起作用。这就是我的Podfile样子。
# Uncomment this line to define a global platform for your project
# platform :ios, '9.0'
# CocoaPods analytics sends network stats synchronously affecting flutter build latency.
ENV['COCOAPODS_DISABLE_STATS'] = 'true' …我有一个FlatButton。单击按钮时，我不希望启动突出显示。我尝试将初始颜色更改为透明，但这没有用。这是我的FlatButton的代码。
Widget button = new Container(
child: new Container(
padding: new EdgeInsets.only(bottom: 20.0),
alignment: Alignment.center,
child: new FlatButton(
onPressed: () {
_onClickSignInButton();
},
splashColor: Colors.transparent,
child: new Stack(
alignment: Alignment.center,
children: <Widget>[
new Image.asset('images/1.0x/button1.png',
),
new Text("SIGN IN",
style: new TextStyle(
color: Colors.white,
fontWeight: FontWeight.bold,
fontSize: 16.0
),
)
],
),
),
),
);
尝试在 Xcode 中构建时出现此错误。我尝试删除派生数据并重新启动 Xcode，但没有任何帮助。
ld: framework not found Flutter
clang: error: linker command failed with exit code 1 (use -v to see invocation)
这是整个错误日志：
Ld /Users/chaythanyanair/Library/Developer/Xcode/DerivedData/Runner-efsxwbzqcezyswaezzytcnxazinn/Build/Products/Debug-iphonesimulator/Runner.app/Runner normal x86_64
cd /Users/chaythanyanair/Documents/Qburst/Learn/flutter_poc/ios
export IPHONEOS_DEPLOYMENT_TARGET=8.0
export PATH="/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/usr/bin:/Applications/Xcode.app/Contents/Developer/usr/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin"
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -arch x86_64 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator11.0.sdk -L/Users/chaythanyanair/Library/Developer/Xcode/DerivedData/Runner-efsxwbzqcezyswaezzytcnxazinn/Build/Products/Debug-iphonesimulator -L/Users/chaythanyanair/Documents/Qburst/Learn/flutter_poc/ios/Pods/EstimoteSDK -L/Users/chaythanyanair/Library/Developer/Xcode/DerivedData/Runner-efsxwbzqcezyswaezzytcnxazinn/Build/Products/Debug-iphonesimulator/Alamofire -L/Users/chaythanyanair/Library/Developer/Xcode/DerivedData/Runner-efsxwbzqcezyswaezzytcnxazinn/Build/Products/Debug-iphonesimulator/SwiftKeychainWrapper -L/Users/chaythanyanair/Library/Developer/Xcode/DerivedData/Runner-efsxwbzqcezyswaezzytcnxazinn/Build/Products/Debug-iphonesimulator/device_info -L/Users/chaythanyanair/Library/Developer/Xcode/DerivedData/Runner-efsxwbzqcezyswaezzytcnxazinn/Build/Products/Debug-iphonesimulator/flutter_secure_storage -L/Users/chaythanyanair/Library/Developer/Xcode/DerivedData/Runner-efsxwbzqcezyswaezzytcnxazinn/Build/Products/Debug-iphonesimulator/shared_preferences -L/Users/chaythanyanair/Documents/Qburst/Learn/flutter_poc/ios/Flutter -F/Users/chaythanyanair/Library/Developer/Xcode/DerivedData/Runner-efsxwbzqcezyswaezzytcnxazinn/Build/Products/Debug-iphonesimulator -F/Users/chaythanyanair/Documents/Qburst/Learn/flutter_poc/ios/Pods/EstimoteSDK/EstimoteSDK -F/Users/chaythanyanair/Documents/Qburst/Learn/flutter_poc/ios/Pods/../../../../flutter/flutter/bin/cache/artifacts/engine/ios -F/Users/chaythanyanair/Documents/Qburst/Learn/flutter_poc/ios/Flutter -filelist /Users/chaythanyanair/Library/Developer/Xcode/DerivedData/Runner-efsxwbzqcezyswaezzytcnxazinn/Build/Intermediates.noindex/Runner.build/Debug-iphonesimulator/Runner.build/Objects-normal/x86_64/Runner.LinkFileList -Xlinker -rpath -Xlinker @executable_path/Frameworks -mios-simulator-version-min=8.0 -dead_strip -Xlinker -object_path_lto -Xlinker /Users/chaythanyanair/Library/Developer/Xcode/DerivedData/Runner-efsxwbzqcezyswaezzytcnxazinn/Build/Intermediates.noindex/Runner.build/Debug-iphonesimulator/Runner.build/Objects-normal/x86_64/Runner_lto.o -Xlinker -export_dynamic -Xlinker -no_deduplicate -Xlinker -objc_abi_version -Xlinker 2 -fobjc-arc -fobjc-link-runtime -L/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/iphonesimulator -Xlinker -add_ast_path -Xlinker /Users/chaythanyanair/Library/Developer/Xcode/DerivedData/Runner-efsxwbzqcezyswaezzytcnxazinn/Build/Intermediates.noindex/Runner.build/Debug-iphonesimulator/Runner.build/Objects-normal/x86_64/Runner.swiftmodule -ObjC -lAlamofire …我正在使用底部导航栏。在某个事件触发器上，我需要在当前屏幕上显示一些警报。
这就是我实现底部导航栏的方式。我有四个标签。在这里，当第4个选项卡的图标_isHomeDetected为true且用户单击该图标（即在索引3上）时，我需要更改该图标，无论用户位于哪个选项卡中，我都必须显示一条警报消息。我该如何做？
class LandingScreen extends StatefulWidget {
static Widget bottomNavigationBar;
..
}
class _LandingScreenState extends State<LandingScreen> {
...
StreamSubscription<String> _subscription;
bool _isHomeDetected = false;
@override
void initState() {
...
_subscription = server.messages.listen(onData, onError: onError);
}
onData(message) {
setState(() {
_isHomeDetected = json.decode(message)["isHomeBeacon"];
});
}
...
@override
Widget build(BuildContext context) {
LandingScreen.bottomNavigationBar = new BottomNavigationBar(
....
);
return new Scaffold(
body: _currentPage,
bottomNavigationBar: LandingScreen.bottomNavigationBar,
);
}
_navigateToScreens(int currentIndex) {
List screens = [
..
];
setState((){
if (!_isHomeDetected || …我想使用python中的类和字典来实现python中设置的内置数据类型。我已经包含了某些基本函数，但我无法执行在其上定义的并集和交集操作。我只想写 c=a+b 其中 a 和 b 是两个字典 c 是另一个字典，其键给出了 'a' 和 'b' 的并集。我尝试了 try 和 except 在我下面的代码中给出的，但我想要一个更好的解决方案。谁能帮我这个？
class My_Set:
def __init__(self,listt):
if listt:
self.dictionary={}
i=0
for x in listt:
self.dictionary[x]=len(x)
i=i+1
else:
self.dictionary={}
def is_element(self,element):
if element in self.dictionary:
return True
else:
return False
def remove(self,element):
if element in self.dictionary:
self.dictionary.pop(element)
else:
print 'element missing'
def add_element(self,element):
self.dictionary.update({element:len(element)})
#return self.dictionary
def union(self,other):
self.dictionary.update(other.dictionary)
return self.dictionary.keys()
在使用解释的方法解雇呈现的Cupertino警报对话动作时,我的整个屏幕都会弹出并且警报对话保留在屏幕上.这是我的代码.
if (deviceList.isEmpty){
var alert = new CupertinoAlertDialog(
title: new Text("Alert"),
content: new Text("There was an error signing in. Please try again."),
actions: <Widget>[
new CupertinoDialogAction(
child: const Text('Discard'),
isDestructiveAction: true,
onPressed: () { Navigator.pop(context, 'Discard'); }
),
new CupertinoDialogAction(
child: const Text('Cancel'),
isDefaultAction: true,
onPressed: () { Navigator.pop(context, 'Cancel'); }
),
],
);
showDialog(context: context, child: alert);
}
我在做什么有什么不对吗？我找不到任何其他解决方案来解雇警报对话.请帮忙.
在升级颤动后运行我的应用程序时，我收到此错误。
error: Invalid kernel binary format version (found 4, expected 6)
我目前处于master, I tried switch the branch to测试阶段。还是没有帮助。这是堆栈跟踪。
2018-05-28 15:22:46.214821+0530 Runner[579:57143] ../../third_party/dart/runtime/vm/kernel_binary.cc: 39: error: Invalid kernel binary format version (found 4, expected 6)
2018-05-28 15:22:46.214912+0530 Runner[579:57143] Dumping native stack trace for thread 7c03
2018-05-28 15:22:46.237923+0530 Runner[579:57143] [0x0000000100fda4a0] dart::Profiler::DumpStackTrace(void*)
2018-05-28 15:22:46.239415+0530 Runner[579:57143] [0x0000000100fda4a0] dart::Profiler::DumpStackTrace(void*)
2018-05-28 15:22:46.271484+0530 Runner[579:57143] [0x0000000000000000] Unknown symbol
2018-05-28 15:22:46.273617+0530 Runner[579:57143] [0x0000000100eda158] dart::kernel::Program::ReadFromBuffer(unsigned char const*, long, bool)
2018-05-28 15:22:46.273681+0530 Runner[579:57143] -- End of DumpStackTrace
这是 的输出flutter …
我已经实现了一个带有几个 TextFormFields 的表单。当我滚动表单时，视图外的 TextFormFields 会丢失输入的数据。这里已经发布了一个类似的问题。我不知道如何使用 TextEditingController 来保存状态，因为我对 Dart 和 Flutter 还很陌生。我什至尝试在这个github repo 之后使用 FormFieldStatePersistor 。那也没有用。关于如何解决问题的任何想法？
嗨我在运行应用程序时收到以下错误可能是什么原因导致问题？
??? EXCEPTION CAUGHT BY WIDGETS LIBRARY ???????????????????????????????????????????????????????????? The following assertion was thrown building Home(dirty, state: _HomeState#f7a67): 'package:flutter/src/widgets/framework.dart': Failed assertion: line 1639: '!children.any((Widget child) => child == null)': is not true.
我正在开发一个Android应用程序,我通过Intents调用Google Translate应用程序.这里描述的过程非常有用,但我无法弄清楚为什么我的应用程序崩溃说"没有找到活动来处理Intent".
提前致谢!
这是我的代码,
public void translate()
{
Intent intent = new Intent();
intent.setAction(Intent.ACTION_SEND);
intent.putExtra(Intent.EXTRA_TEXT, "hello");
intent.putExtra("key_text_input", "hello");
intent.putExtra("key_text_output", "");
intent.putExtra("key_language_from", "en");
intent.putExtra("key_language_to", "mal");
intent.putExtra("key_suggest_translation", "");
intent.putExtra("key_from_floating_window", false);
new ComponentName(
"com.google.android.apps.translate",
"com.google.android.apps.translate.HomeActivity");
startActivity(intent);
}
这就是我的logcat显示的内容
04-20 07:29:01.647: E/AndroidRuntime(31465): android.content.ActivityNotFoundException: No Activity found to handle Intent { act=android.intent.action.SEND flg=0x1 (has clip) (has extras) }
04-20 07:29:01.647: E/AndroidRuntime(31465): at android.app.Instrumentation.checkStartActivityResult(Instrumentation.java:1628)
04-20 07:29:01.647: E/AndroidRuntime(31465): at android.app.Instrumentation.execStartActivity(Instrumentation.java:1423)
04-20 07:29:01.647: E/AndroidRuntime(31465): at android.app.Activity.startActivityForResult(Activity.java:3388)
04-20 07:29:01.647: E/AndroidRuntime(31465): at android.app.Activity.startActivityForResult(Activity.java:3349)
04-20 07:29:01.647: E/AndroidRuntime(31465): at android.app.Activity.startActivity(Activity.java:3584) …我有两个类， auser_api_manager和 a base_api_manager。从user_api_manager我调用该get方法base_api_manager执行 http get 请求并返回一个Future<String>. 该get执行请求，但我不是结果传递给我的user_api_manager班。回调结果始终为空。
这是我的 user_api_manager.dart
static Future<Map<String,dynamic>> forgotPasswordAPI(String email) async{
String url = Constants.BASE_URL + Constants.FORGOT_PASSWORD_URL + email;
await BaseApiManager.get(url: url).then((val) {
var response = JSON.decode(val);
var status = response['status'];
String message = '';
print(response);
switch (response['status']) {
case Constants.SUCCESS:
message = Constants.SUCCESS_RESPONSE;
break;
case Constants.SERVER_ERROR:
message = Constants.SERVER_ERROR_MESSAGE;
break;
case Constants.UNAUTHORISED:
message = Constants.UNAUTHORISED_MESSAGE;
break;
}
return {'status':status,'message':message};
}); …