我在Android中玩碎片。
我知道我可以通过使用以下代码更改一个片段:
FragmentManager fragMgr = getSupportFragmentManager();
FragmentTransaction fragTrans = fragMgr.beginTransaction();
MyFragment myFragment = new MyFragment(); //my custom fragment
fragTrans.replace(android.R.id.content, myFragment);
fragTrans.addToBackStack(null);
fragTrans.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
fragTrans.commit();
我的问题是，在Java文件中，如何获得当前显示的片段实例?
当前回答
我遇到了一个类似的问题，我想知道当返回键被按下时最后显示的片段是什么。我用了一个非常简单的方法。每次我打开一个片段，在onCreate()方法中，我在我的单例中设置了一个变量(用你的片段的名称替换“myFragment”)
MySingleton.currentFragment = myFragment.class;
变量在单例中声明为
public static Class currentFragment = null;
然后在onBackPressed()中检查
if (MySingleton.currentFragment == myFragment.class){
// do something
return;
}
super.onBackPressed();
确保调用super.onBackPressed();在“返回”之后，否则应用程序将处理返回键，这在我的情况下导致应用程序终止。
其他回答
1)
ft.replace(R.id.content_frame, fragment, **tag**).commit();
2)
FragmentManager fragmentManager = getSupportFragmentManager();
Fragment currentFragment = fragmentManager.findFragmentById(R.id.content_frame);
3)
if (currentFragment.getTag().equals(**"Fragment_Main"**))
{
//Do something
}
else
if (currentFragment.getTag().equals(**"Fragment_DM"**))
{
//Do something
}
我的方法是基于try / catch，如下所示:
MyFragment viewer = null;
if(getFragmentManager().findFragmentByTag(MY_TAG_FRAGMENT) instanceOf MyFragment){
viewer = (MyFragment) getFragmentManager().findFragmentByTag(MY_TAG_FRAGMENT);
}
但也许有更好的办法……
简单的方法:
Fragment fr=getSupportFragmentManager().findFragmentById(R.id.fragment_container);
String fragmentName = fr.getClass().getSimpleName();
如果你有嵌套片段，如viewpagers内部viewpagers等 你想要得到所有嵌套的片段。
感谢Matt Mombrea的好意，回答一个稍微调整的版本。
private List<Fragment> getVisibleFragments(List<Fragment> searchFragments, List<Fragment> visibleFragments) {
if (searchFragments != null && searchFragments.size() > 0) {
for (Fragment fragment : searchFragments) {
List<Fragment> nestedFragments = new ArrayList<>();
List<Fragment> childFMFragments = fragment.getChildFragmentManager().getFragments();
List<Fragment> fmFragments = fragment.getFragmentManager().getFragments();
fmFragments.retainAll(childFMFragments);
nestedFragments.addAll(childFMFragments);
nestedFragments.addAll(fmFragments);
getVisibleFragments(nestedFragments, visibleFragments);
if (fragment != null && fragment.isVisible()) {
visibleFragments.add(fragment);
}
}
}
return visibleFragments;
}
用法如下:
List<Fragment> allVisibleFragments = getVisibleFragments(searchFragments, visibleFragments);
例如:
List<Fragment> visibleFragments = new ArrayList<>();
List<Fragment> searchFragments = MainActivity.this.getSupportFragmentManager().getFragments();
Toast.makeText(this, ""+getVisibleFragments(searchFragments, visibleFragments), Toast.LENGTH_LONG).show();
你也可以很容易地在logcat中使用URL，它将重定向到当前片段源代码的源代码。首先，你需要在主机活动中添加一个OnBackStackChangedListener，比如-
activity.getChildFragmentManager().addOnBackStackChangedListener(backStackListener);
OnBackStackChangedListener的实现是-
public FragmentManager.OnBackStackChangedListener backStackListener = () -> {
String simpleName = "";
String stackName = getStackTopName().trim();
if (Validator.isValid(stackName) && stackName.length() > 0) {
simpleName = stackName.substring(Objects.requireNonNull(stackName).lastIndexOf('.') + 1).trim();
List<Fragment >
fragmentList = getChildFragmentManager().getFragments();
Fragment myCurrentFragment;
for (int i = 0; i < fragmentList.size(); i++) {
myCurrentFragment= fragmentList.get(i);
if (myCurrentFragment.getClass().getSimpleName().equals(simpleName)) {
//Now you get the current displaying fragment assigned in myCurrentFragment.
break;
}
myFragment = null;
}
}
//The code below is for the source code redirectable logcat which would be optional for you.
StackTraceElement stackTraceElement = new StackTraceElement(simpleName, "", simpleName + ".java", 50);
String fileName = stackTraceElement.getFileName();
if (fileName == null) fileName = "";
final String info = "Current Fragment is:" + "(" + fileName + ":" +
stackTraceElement.getLineNumber() + ")";
Log.d("now", info + "\n\n");
};
getStackTopName()方法是-
public String getStackTopName() {
FragmentManager.BackStackEntry backEntry = null;
FragmentManager fragmentManager = getChildFragmentManager();
if (fragmentManager != null) {
if (getChildFragmentManager().getBackStackEntryCount() > 0)
backEntry = getChildFragmentManager().getBackStackEntryAt(
getChildFragmentManager().getBackStackEntryCount() - 1
);
}
return backEntry != null ? backEntry.getName() : null;
}
