要从异步操作中获取值,可以在方法中定义自己的回调,以便在从这些操作返回时使用这些值.

这是Java的方法

首先定义一个接口：

interface Callback {

void myResponseCallback(YourReturnType result);//whatever your return type is: string, integer, etc.

}

接下来,将您的方法签名更改为：

public void foo(Callback callback) { // make your method, which was previously returning something, return void, and add in the new callback interface.

接下来,无论您以前想要使用这些值,请添加以下行：

callback.myResponseCallback(yourResponseObject);

举个例子 ：

@Override

public void onSuccess(QuerySnapshot documentSnapshots) {

// create your object you want to return here

String bar = document.get("something").toString();

callback.myResponseCallback(bar);

})

现在,您之前调用的方法称为foo：

foo(new Callback() {

@Override

public void myResponseCallback(YourReturnType result) {

//here, this result parameter that comes through is your api call result to use, so use this result right here to do any operation you previously wanted to do.

}

});

}

你是怎么为Kotlin做的？

(作为您只关心单个结果的基本示例)

首先将方法签名更改为以下内容：

fun foo(callback:(YourReturnType) -> Unit) {

.....

然后,在异步操作的结果中：

firestore.collection("something").document("document").get().addOnSuccessListener {

val bar = it.get("something").toString()

callback.invoke(bar)

}

那么,你以前称之为foo的方法,你现在这样做：

foo { result->

here, this result parameter that comes through is your api call result to use, so use this result right here to do any operation you previously wanted to do.

}

如果你的foo方法以前参数：

fun foo(value:SomeType, callback:(YourType) -> Unit)

你只需将其更改为：

foo(yourValueHere) { result ->

here, this result parameter that comes through is your api call result to use, so use this result right here to do any operation you previously wanted to do.

}