Android 运行阻塞请求
我了解到Firebase在后台线程上运行其操作,在UI线程上运行其回调 是否有办法运行阻止Firebase操作 例如: 我知道Android 运行阻塞请求,android,firebase,firebase-realtime-database,Android,Firebase,Firebase Realtime Database,我了解到Firebase在后台线程上运行其操作,在UI线程上运行其回调 是否有办法运行阻止Firebase操作 例如: 我知道setValue()不会返回布尔值,我是问是否有类似的API可以执行以下代码 // we are in a background thread DatabaseReference ref = FirebaseDatabase.getInstance().getReference(); boolean success = ref.child("user").child(
setValue()
不会返回布尔值,我是问是否有类似的API可以执行以下代码
// we are in a background thread
DatabaseReference ref = FirebaseDatabase.getInstance().getReference();
boolean success = ref.child("user").child("name").setValue("Arthur");
// code is blocked until operation completes
Log.d("MY_TAG", "successfull operation:" + success);
FirebaseDatabase API不包括块形式的。您可以在工作线程(非主线程)中使用返回的代码在自己的代码中添加阻塞: A可用于阻塞读取。由于侦听器回调在主线程上运行,因此此代码只能在另一个线程上运行。如果在主线程上运行,它会死锁
final Semaphore sem = new Semaphore(0);
DatabaseReference ref = FirebaseDatabase.getInstance().getReference();
ref.child("user").child("name").addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
String name = dataSnapshot.getValue(String.class);
Log.i("MY_TAG", "Name=" + name);
sem.release();
}
@Override
public void onCancelled(DatabaseError databaseError) {
Log.e("MY_TAG", "onCancelled: " + databaseError.getMessage());
sem.release();
}
});
try {
sem.acquire();
} catch (InterruptedException e) {
Log.w("MY_TAG", "Interrupted");
}
您还可以使用任务进行阻塞读取(脱离主线程):
final TaskCompletionSource taskSource=new TaskCompletionSource();
final Task Task=taskSource.getTask();
DatabaseReference ref=FirebaseDatabase.getInstance().getReference();
ref.child(“用户”).child(“名称”).addListenerForSingleValueEvent(新值EventListener()){
@凌驾
公共void onDataChange(DataSnapshot DataSnapshot){
taskSource.setResult(dataSnapshot);
}
@凌驾
已取消的公共void(DatabaseError DatabaseError){
setException(databaseError.toException());
}
});
试一试{
任务。等待(任务);
字符串名称=task.getResult().getValue(String.class);
Log.i(“我的标签”,“名称=”+名称);
}捕获(执行例外){
Log.e(“我的标签”,“读取失败:”+task.getException().getMessage());
}捕捉(中断异常e){
Log.w(“我的标签”,“读取中断”);
}
谢谢qbix!这似乎对setValue()起到了作用。有没有一种方法可以对“读取”操作执行相同的操作?(即,将DatabaseReference的addListenerForSingleValueEvent()替换为我可以等待的任务?
final Semaphore sem = new Semaphore(0);
DatabaseReference ref = FirebaseDatabase.getInstance().getReference();
ref.child("user").child("name").addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
String name = dataSnapshot.getValue(String.class);
Log.i("MY_TAG", "Name=" + name);
sem.release();
}
@Override
public void onCancelled(DatabaseError databaseError) {
Log.e("MY_TAG", "onCancelled: " + databaseError.getMessage());
sem.release();
}
});
try {
sem.acquire();
} catch (InterruptedException e) {
Log.w("MY_TAG", "Interrupted");
}
final TaskCompletionSource<DataSnapshot> taskSource = new TaskCompletionSource<>();
final Task<DataSnapshot> task = taskSource.getTask();
DatabaseReference ref = FirebaseDatabase.getInstance().getReference();
ref.child("user").child("name").addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
taskSource.setResult(dataSnapshot);
}
@Override
public void onCancelled(DatabaseError databaseError) {
taskSource.setException(databaseError.toException());
}
});
try {
Tasks.await(task);
String name = task.getResult().getValue(String.class);
Log.i("MY_TAG", "Name=" + name);
} catch (ExecutionException e) {
Log.e("MY_TAG", "Read failed: " + task.getException().getMessage());
} catch (InterruptedException e) {
Log.w("MY_TAG", "Read interrupted");
}