我正在编写一个方法,我想查询数据库并在查询完成后执行另一个方法。不过,由于对数据库的调用是异步的,我似乎无法弄清楚如何在数据库调用完成之前停止主要执行流程,如下所示:
public void getUserFromEmail(String email) {
Firebase usersRef = rootRef.child("users");
//Asynchronous database call, want to stop everything else
usersRef.orderByKey().equalTo(email).addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
}
@Override
public void onCancelled(FirebaseError firebaseError) {
System.out.println(firebaseError.getMessage());
}
});
//Perform some more operations after database call is finished
}
我习惯于在 Nodejs 中使用异步回调,但我不知道在 Java 中是否有任何等效的控制执行流的方法。有什么简单的方法可以实现我想做的事情吗?
最佳答案
你无法停止主流程,主线程将继续运行。 (除非您以其他方式停止它,但这会导致“应用程序未响应”,所以不要这样做)。
只需在回调中执行操作即可。
public void getUserFromEmail(String email) {
Firebase usersRef = rootRef.child("users");
//Asynchronous database call, want to stop everything else
usersRef.orderByKey().equalTo(email).addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
// Perform some more operations after database call is finished
// OR... callSomeMethod();
}
@Override
public void onCancelled(FirebaseError firebaseError) {
System.out.println(firebaseError.getMessage());
}
});
}
public void callSomeMethod() {
// Perform some more operations after database call is finished
}
如果您有 Node 背景,那么这看起来可能很相似。将函数传递给 getUserFromEmail
public void otherMethod() {
getUserFromEmail("steve@example.com", new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
// Perform some more operations after database call is finished
}
@Override
public void onCancelled(FirebaseError firebaseError) {
System.out.println(firebaseError.getMessage());
}
});
}
public void getUserFromEmail(String email, ValueEventListener listener) {
rootRef.child("users")
.orderByKey()
.equalTo(email)
.addListenerForSingleValueEvent(listener);
}
关于java - Java 中的异步执行流程,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/39985535/