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我已阅读了大量有关此(异步和期货)的帖子和文章,并且我不确定当前情况如何。我尝试了许多不同的变化。如何按顺序处理异步代码
我试图在序列下面的代码的过程:
import 'dart:async' as async;
import 'dart:io';
import 'dart:math';
import 'package:postgresql/postgresql.dart' as pg;
var uri = 'postgres://admin:[email protected]:5432/testdb';
List lgNames = ['Peter', 'Robert', 'Mary', 'Marg', 'William',
'Vern', 'Dermot', 'Monty', 'Peggy', 'Sue', 'William'];
List lgUsed = [];
Random rand1 = new Random();
void main() {
pg.connect(uri).then((oDb) {
print ("Connected to database");
fClearTable(oDb).then((String sResult){
print(sResult);
for (int iPos = 0; iPos < 3; iPos++) {
fListTable(oDb, "Select before Insert number ${iPos+1}").then((String sResult) =>
print(sResult));
fInsertData(oDb, "Insert Number ${iPos+1}").then((String sResult) =>
print(sResult));
fListTable(oDb, "Select after Insert number ${iPos+1}").then((String sResult) =>
print(sResult));
}
});
});
}
async.Future<String> fClearTable(oDb) {
async.Completer oCompleter = new async.Completer();
oDb.execute("DELETE FROM test01").then((oResult){
oCompleter.complete("Table has been cleared");
});
return oCompleter.future;
}
async.Future<List> fListTable(oDb, sMsg) {
async.Completer oCompleter = new async.Completer();
oDb.query("SELECT * FROM test01").toList().then((lResult){
String sResult = "$sMsg = $lResult";
oCompleter.complete(sResult);
});
return oCompleter.future;
}
async.Future<String> fInsertData(oDb, sMsg) {
async.Completer oCompleter = new async.Completer();
oDb.execute("Start Transaction").then((oResult){
String sName;
for (bool tFound = true; tFound;) {
int iPos = rand1.nextInt(10);
sName = lgNames[iPos];
tFound = false; // init
for (iPos = 0; iPos < lgUsed.length && !tFound; iPos++){
tFound = (sName == lgUsed[iPos]);
}
}
lgUsed.add(sName);
String sSql = """INSERT INTO test01 (name)
VALUES ('$sName')""";
print("$sSql");
oDb.execute(sSql).then((oVal){
oDb.execute("COMMIT").then((oVal){
oCompleter.complete(sMsg);
});
});
});
return oCompleter.future;
}
该计划的目的是循环三次: a)选择表 B)插入一行到表中。 c)选择表
程序的输出结果清楚地显示了所有三个插入。
从程序的输出如下:显示
Connected to database
Table has been cleared
Select before Insert number 1 = []
INSERT INTO test01 (name)
VALUES ('Vern')
Select after Insert number 1 = []
Select before Insert number 2 = []
INSERT INTO test01 (name)
VALUES ('Peter')
Select after Insert number 2 = []
Select before Insert number 3 = []
INSERT INTO test01 (name)
VALUES ('Robert')
Select after Insert number 3 = []
Insert Number 1
Insert Number 2
Insert Number 3
A选择在节目结束的psql:
testdb=# select * from test01;
id | name
-----+--------
157 | Vern
158 | Peter
159 | Robert
(3 rows)
有没有办法达到我想要的IE浏览器。对于插入后的选择显示表中的新值?
欢迎任何相关的意见。