Javascript“承诺”如何使同步
我正在使用Ionic2/Typescript 我有两个承诺,我想在我继续之前完成,即同步。所以我把对这两个函数的调用放在一个承诺中。全部…,期望它们在调用resolve之前完成 我有以下代码:Javascript“承诺”如何使同步,javascript,sqlite,typescript,Javascript,Sqlite,Typescript,我正在使用Ionic2/Typescript 我有两个承诺,我想在我继续之前完成,即同步。所以我把对这两个函数的调用放在一个承诺中。全部…,期望它们在调用resolve之前完成 我有以下代码: public openDatabase(): Promise<Array<Message>> { let promise: Promise<Array<Message>> = new Promise<Array<Message>&g
public openDatabase(): Promise<Array<Message>> {
let promise: Promise<Array<Message>> = new Promise<Array<Message>>(resolve => {
if (false && this.database && this.database != null) {
Promise.all([this.refreshChats(this.database), this.refreshMessages(this.database)]).then(() => {
console.log('openDatabase1: resolve');
resolve(this.messages);
});
} else {
this.database = new SQLite();
this.database.openDatabase({
name: "data.db",
location: "default"
}).then(() => {
Promise.all([this.refreshChats(this.database), this.refreshMessages(this.database)]).then(() => {
console.log('openDatabase2: resolve');
resolve(this.messages);
});
}, (error) => {
console.log("OPEN ERROR: ", error);
});
}
});
return promise;
}
public refreshChats(db: any): Promise<any> {
console.log('refreshChats ');
return db.executeSql("SELECT * FROM chats", [])
.then((chatData) => {
let promises: Array<any> = [];
this.chats = [];
if (chatData.rows.length > 0) {
for (var i = 0; i < chatData.rows.length; i++) {
promises.push(this.populateChat(db, chatData.rows.item(i)));
}
}
Promise.all(promises).then(() => {
console.log('refreshChats return this.chats.length = ' + this.chats.length);
return this.chats;
});
})
.catch(error => {
console.log("ERROR REFRESHING CHATS: " + JSON.stringify(error));
console.log(error);
});
}
对于如何构建我的承诺的任何建议,我都非常感谢。您需要从内部承诺回访中返回新的承诺:
public openDatabase(): Promise<Array<Message>> {
let promise: Promise<Array<Message>> = new Promise<Array<Message>>(resolve => {
if (false && this.database && this.database != null) {
return Promise.all([this.refreshChats(this.database), this.refreshMessages(this.database)]).then(() => {
console.log('openDatabase1: resolve');
resolve(this.messages);
});
} else {
this.database = new SQLite();
return this.database.openDatabase({
name: "data.db",
location: "default"
}).then(() => {
return Promise.all([this.refreshChats(this.database), this.refreshMessages(this.database)]).then(() => {
console.log('openDatabase2: resolve');
resolve(this.messages);
});
}, (error) => {
console.log("OPEN ERROR: ", error);
});
}
});
return promise;
}
public refreshChats(db: any): Promise<any> {
console.log('refreshChats ');
return db.executeSql("SELECT * FROM chats", [])
.then((chatData) => {
let promises: Array<any> = [];
this.chats = [];
if (chatData.rows.length > 0) {
for (var i = 0; i < chatData.rows.length; i++) {
promises.push(this.populateChat(db, chatData.rows.item(i)));
}
}
return Promise.all(promises).then(() => {
console.log('refreshChats return this.chats.length = ' + this.chats.length);
return this.chats;
});
})
.catch(error => {
console.log("ERROR REFRESHING CHATS: " + JSON.stringify(error));
console.log(error);
});
}
注意,返回Promise.all并返回this.database.openDatabase
public openDatabase(): Promise<Array<Message>> {
let promise: Promise<Array<Message>> = new Promise<Array<Message>>(resolve => {
if (false && this.database && this.database != null) {
return Promise.all([this.refreshChats(this.database), this.refreshMessages(this.database)]).then(() => {
console.log('openDatabase1: resolve');
resolve(this.messages);
});
} else {
this.database = new SQLite();
return this.database.openDatabase({
name: "data.db",
location: "default"
}).then(() => {
return Promise.all([this.refreshChats(this.database), this.refreshMessages(this.database)]).then(() => {
console.log('openDatabase2: resolve');
resolve(this.messages);
});
}, (error) => {
console.log("OPEN ERROR: ", error);
});
}
});
return promise;
}
public refreshChats(db: any): Promise<any> {
console.log('refreshChats ');
return db.executeSql("SELECT * FROM chats", [])
.then((chatData) => {
let promises: Array<any> = [];
this.chats = [];
if (chatData.rows.length > 0) {
for (var i = 0; i < chatData.rows.length; i++) {
promises.push(this.populateChat(db, chatData.rows.item(i)));
}
}
return Promise.all(promises).then(() => {
console.log('refreshChats return this.chats.length = ' + this.chats.length);
return this.chats;
});
})
.catch(error => {
console.log("ERROR REFRESHING CHATS: " + JSON.stringify(error));
console.log(error);
});
}