英文:
How to exit if else and for loop in Flutter?
问题
我计划在Flutter中退出if else或循环语句，当检测到列表中存在重复项时。但是，当我在if和else语句中放置break时，它并不起作用良好。如果我在if中放置break，那么即使if语句中有break退出循环，else语句仍将继续执行。如果我在else语句中放置break，那么由于else语句中的break会影响i++，if语句将根本不执行。而如果我在if和else语句中都放置break，它会显示我的i++是死代码。
以下是代码：
void addFavourite() {
favouriteCountry.add(properties[0]['name']);
}
void checkDuplicates() {
int length = favouriteCountry.length;
String cName = properties[0]['name'];
if (length > 0) {
for (int i = 0; i < length; i++) {
String name = favouriteCountry[i];
print(name);
if (name == cName) {
print(length);
showDialog<void>(
context: context,
barrierDismissible: false,
builder: (BuildContext context) {
return AlertDialog(
title: const Text('Duplicated action, country already added to list.'),
content: SingleChildScrollView(
child: ListBody(
children: const <Widget>[
Text('You really liked this country huh?'),
],
),
),
actions: <Widget>[
TextButton(
child: const Text('OK'),
onPressed: () {
Navigator.of(context).pop();
},
),
],
);
},
);
break;
} else {
addFavourite();
displayAddFavourite();
print("object");
}
}
} else {
addFavourite();
displayAddFavourite();
print("object1");
}
}
英文:
I am planning to exit my if else or loop statement in Flutter when it detects there are duplicated item in my lists. But it does not work well when I put break in the if and else statement. When I put break in if, then the else statement will continue to execute even when the if statement had break the loop. If I put break in the else statement, then the if statement will not execute at all since the break in else statement will affect i++. While if I put break in both if and else statement, it shows my i++ is dead code.
Here are the code:
void addFavourite() {
favouriteCountry.add(properties[0]['name']);
}
void checkDuplicates() {
int length = favouriteCountry.length;
String cName = properties[0]['name'];
if (length > 0) {
for (int i = 0; i < length; i++) {
String name = favouriteCountry[i];
print(name);
if (name == cName) {
print(length);
showDialog<void>(
context: context,
barrierDismissible: false, // user must tap button!
builder: (BuildContext context) {
return AlertDialog(
title: const Text(
'Duplicated action, country already added to list.'),
content: SingleChildScrollView(
child: ListBody(
children: const <Widget>[
Text('You really liked this country huh?'),
],
),
),
actions: <Widget>[
TextButton(
child: const Text('OK'),
onPressed: () {
Navigator.of(context).pop();
},
),
],
);
},
);
break;
} else {
addFavourite();
displayAddFavourite();
print("object");
}
}
} else {
addFavourite();
displayAddFavourite();
print("object1");
}
}
I tried to put i++ in both if and else statement, but it does not work. So if there is anything I can add into my code to make it work. Please feel free to enlighten me. Thanks in advance!
答案1
得分: 0
你可以考虑使用一个 `flag` 并相应地显示 `dialog`。
英文:
You can probably consider using a flag and show the dialog accordingly.
void checkDuplicates() {
int length = favouriteCountry.length;
String cName = properties[0]['name'];
bool foundDuplicate = false; // set this flag
for (int i = 0; i < length; i++) {
String name = favouriteCountry[i];
print(name);
if (name == cName) {
foundDuplicate = true;
break;
}
}
if (foundDuplicate) {
showDialog<void>(
context: context,
barrierDismissible: false,
builder: (BuildContext context) {
// ...
},
);
} else {
addFavourite();
displayAddFavourite();
print("object");
}
}
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