我正在使用StreamBuilder其中，我有一個任務串列，這些任務從快照中獲取輸入并相應地顯示資料，但是在處理快照資料時我遇到了一個空安全問題。代碼如下所示：
StreamBuilder<List<Task>>(
stream: DatabaseService()
.getCompletedTasks(orderName),
builder: (context, snapshot) {
List<Task> completedTasks =
snapshot.data!;
return snapshot.data!.isEmpty
? Container(
alignment:
Alignment.center,
child: Text(
"You don't have any completed tasks.",
style: TextStyle(
fontSize: 20,
fontFamily:
"Roboto",
color: Colors.black,
),
),
)
: Container(
child: Flexible(
flex: 0,
child: ListView
.separated(
physics:
const NeverScrollableScrollPhysics(),
shrinkWrap: true,
separatorBuilder:
(context,
index) =>
const SizedBox(
height: 5,
),
itemCount:
completedTasks
.length,
itemBuilder:
(context,
index) {
return Dismissible(
background:
Container(
color: Colors
.red,
child:
const Align(
alignment:
Alignment
.centerLeft,
child:
Padding(
padding:
EdgeInsets.all(
15.0),
child:
Icon(
Icons
.delete,
color: Colors
.white,
),
),
),
),
secondaryBackground:
Container(
color: Colors
.red,
child:
const Align(
alignment:
Alignment
.centerRight,
child:
Padding(
padding:
EdgeInsets.all(
15.0),
child:
Icon(
Icons
.delete,
color: Colors
.white,
),
),
),
),
key:
UniqueKey(),
onDismissed:
(direction) {
DatabaseService()
.deleteTask(
completedTasks[index]
.id);
AwesomeNotifications()
.cancelSchedule(
completedTasks[index]
.id);
},
child: Item(
task:
completedTasks[
index],
),
);
},
),
),
);
}),
一切正常，但只是在短時間內彈出空安全錯誤。
uj5u.com熱心網友回復：
你在這里強制非空值
List<Task> completedTasks =snapshot.data!;
// this caused issue
像這樣添加條件
StreamBuilder<List<Task>>(
stream: DatabaseService().getCompletedTasks(orderName),
builder: (context, snapshot) {
if(snapshot.hasData){
// Returns whether this snapshot contains a non-null [data] value.
//your widget list
// display widget when it success
}else if(snapshot.hasError){
//your widget show error state
// display when error occured
}else{
// your default widget,
// like loader , etc
// display while loading run the function stream
}
)
uj5u.com熱心網友回復：
在初始階段加載流資料時添加 1 個條件。
StreamBuilder<List<Task>>(
stream: DatabaseService()
.getCompletedTasks(orderName),
builder: (context, snapshot) {
// Add this condition.
if(!snapshot.hasData){
return Center(child: CircularProgressIndicator());
}
List<Task> completedTasks =
snapshot.data!;
return snapshot.data!.isEmpty
? Container(
alignment:
Alignment.center,
child: Text(
"You don't have any completed tasks.",
style: TextStyle(
fontSize: 20,
fontFamily:
"Roboto",
color: Colors.black,
),
),
)
: Container(
child: Flexible(
flex: 0,
child: ListView
.separated(
physics:
const NeverScrollableScrollPhysics(),
shrinkWrap: true,
separatorBuilder:
(context,
index) =>
const SizedBox(
height: 5,
),
itemCount:
completedTasks
.length,
itemBuilder:
(context,
index) {
return Dismissible(
background:
Container(
color: Colors
.red,
child:
const Align(
alignment:
Alignment
.centerLeft,
child:
Padding(
padding:
EdgeInsets.all(
15.0),
child:
Icon(
Icons
.delete,
color: Colors
.white,
),
),
),
),
secondaryBackground:
Container(
color: Colors
.red,
child:
const Align(
alignment:
Alignment
.centerRight,
child:
Padding(
padding:
EdgeInsets.all(
15.0),
child:
Icon(
Icons
.delete,
color: Colors
.white,
),
),
),
),
key:
UniqueKey(),
onDismissed:
(direction) {
DatabaseService()
.deleteTask(
completedTasks[index]
.id);
AwesomeNotifications()
.cancelSchedule(
completedTasks[index]
.id);
},
child: Item(
task:
completedTasks[
index],
),
);
},
),
),
);
}),
轉載請註明出處，本文鏈接：https://www.uj5u.com/net/507508.html
標籤：Google Cloud Collective 扑 火力基地 镖