Angular Ionic与Firebase数据库Ref多次调用
我正在使用Ionic3和AngularFire2与Firebase数据库交互 我有以下代码: tsAngular Ionic与Firebase数据库Ref多次调用,angular,firebase,ionic-framework,firebase-realtime-database,ionic3,Angular,Firebase,Ionic Framework,Firebase Realtime Database,Ionic3,我正在使用Ionic3和AngularFire2与Firebase数据库交互 我有以下代码: ts createMessage(chatItem: any, messageText: string): Promise<firebase.database.ThenableReference> { let offsetRef: firebase.database.Reference = firebase.database().ref(".info/serverTimeOffset
createMessage(chatItem: any, messageText: string): Promise<firebase.database.ThenableReference> {
let offsetRef: firebase.database.Reference = firebase.database().ref(".info/serverTimeOffset");
return new Promise<firebase.database.ThenableReference>((resolve) => {
offsetRef.on("value", (snap: firebase.database.DataSnapshot) => {
var offset = snap.val();
var negativeTimestamp = (new Date().getTime() + offset) * -1;
chatItem.readByReceiver = false;
if (chatItem && !chatItem.$key && chatItem.key) {
chatItem.$key = chatItem.key;
}
this.updateChat(chatItem);
let ref: firebase.database.ThenableReference = this.af.database.list('/message').push({
chatId: chatItem.$key,
memberId1: this.me.uid,
memberId2: this.you.uid,
username: this.me.displayName,
message_text: messageText,
timestamp: firebase.database.ServerValue.TIMESTAMP,
negativtimestamp: negativeTimestamp,
readByReceiver: false
});
resolve(ref);
});
});
}
我希望每次调用函数时只执行一次<我认为code>offsetRef.on的行为就像一个可观察的对象
问题
确保代码只执行一次的最佳方法是什么
谢谢。你说得对,它像一个可观察的物体一样工作,每次值改变时都会被触发。要确保它只运行一次,请使用
one('value')
。
更多信息:
非常感谢。我将测试它。
offsetRef.on("value", (snap: firebase.database.DataSnapshot) => {
// breakpoint getting executed more than once here
});
offsetRef.once("value").then((snapshot) => {
// cod will be executed once here
});