Android - 在 UI 片段中保留对象 [英] Android - Retain objects in UI Fragment
问题描述
在我的项目中,我最初使用这个方案:
In my project, I originally use this scheme:
Activity A
(UI) > Fragment B
(non-UI) > Adapter + AsyncTask
Activity
A
(UI) > FragmentB
(non-UI) > Adapter + AsyncTask
B
保留与setRetainInstance(true)
并更新A
UIA
使用getFragmentManager()
实例化 B
retained withsetRetainInstance(true)
and updatingA
UIA
instantiateB
withgetFragmentManager()
C
保留了setRetainInstance(true)
并更新了B
UIB
使用getChildFragmentManager()
实例化 C
retained withsetRetainInstance(true)
and updatingB
UIB
instantiateC
withgetChildFragmentManager()
B
但是我现在需要使用UI Fragments,所以我想使用这个方案:
But I now need to use UI Fragments, so I thought to use this scheme:
Activity A
> Fragment B
(UI) > Fragment C
(非 UI) > Adapter + AsyncTask
Activity
A
> FragmentB
(UI) > FragmentC
(non-UI) > Adapter + AsyncTask
C
但似乎不可能:
Caused by: java.lang.IllegalStateException:
Can't retain fragements that are nested in other fragments
我尝试使用 getFragmentManager()
而不是 getChildFragmentManager()
来实例化 C
但我遇到了一些问题.
I tried to instantiate C
with getFragmentManager()
instead of getChildFragmentManager()
but I had some problems.
在 Fragment 中保留对象和管理 AsyncTask 的最佳做法是什么?
What is the best practice to retain objects and manage AsyncTasks in a Fragment?
推荐答案
我终于开发了一个小助手类:
I finally develop a little helper class:
public class RetainFragment<F extends Fragment> extends Fragment {
private static <F extends Fragment> String tag(F ui, Object id) {
return ui.getClass().getName() + id.toString();
}
public static <F extends Fragment> Fragment get(F ui, Object id) {
return ui.getFragmentManager().findFragmentByTag(tag(ui, id));
}
public F ui;
public Object id;
@Override
public void onCreate(Bundle state) {
super.onCreate(state);
setRetainInstance(true);
}
public void link(F ui, Object id) {
this.id = id;
this.ui = ui;
if (get(ui, id) == null) {
ui.getFragmentManager()
.beginTransaction()
.add(this, tag(ui, id))
.commit();
}
}
public void unlink() {
if (get(ui, id) != null) {
ui.getFragmentManager()
.beginTransaction()
.remove(this)
.commit();
}
ui = null;
id = null;
}
}
现在,在 UI Fragments 中,我只写:
And now, in UI Fragments, I only write:
public class UiFragment extends Fragment {
private static class Retain extends RetainFragment<UiFragment> {
private MyAsyncTask task; // Objects to retain over
private MyAdapter adapter; // configuration changes
}
private Retain retain;
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
retain = (Retain) Retain.get(this, 0);
if (retain == null) {
retain = new Retain();
// Retained objects initialization
retain.adapter = new MyAdapter();
}
retain.link(this, 0);
}
@Override
public void onDetach() {
if (isRemoving()) {
// Retained objects terminate
if (retain.task != null) {
retain.task.cancel(true);
}
retain.unlink();
}
super.onDetach();
}
private void update() {
if (!isDetached()) {
// Update UI fragment
}
}
}
在retain.task.onPostExecute()
中:
retain.ui.update(); // Reference to the last ui fragment instance linked
并在 UI 片段启动时启动任务:
And to launch the task at UI fragment startup:
private static class Retain extends RetainFragment<UiFragment> {
private MyAsyncTask task; // Objects to retain over
private MyAdapter adapter; // configuration changes
@Override
public void onCreate(Bundle state) {
super.onCreate(state);
ui.onRetainCreated();
}
}
private void onRetainCreated() {
retain.task = new MyAsyncTask() {
@Override
protected void onPostExecute(Void result) {
retain.ui.update();
}
};
retain.task.execute();
}
这篇关于Android - 在 UI 片段中保留对象的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!