我正在学习如何使用片段。我有三个Fragment
实例,它们在课程顶部初始化。我将片段添加到这样的活动:
声明和初始化:
Fragment A = new AFragment();
Fragment B = new BFragment();
Fragment C = new CFragment();
更换/添加:
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.content_frame, A);
ft.addToBackStack(null);
ft.commit();
这些片段工作正常。每个片段都附加到活动,并保存到后台堆栈没有任何问题。
因此,当我启动A
,C
,然后B
时,堆栈看起来像这样:
| |
|B|
|C|
|A|
___
当我按下“后退”按钮时,B
被摧毁,C
被恢复。
但是,当我第二次启动片段A
时,它不会从后端堆栈恢复,而是添加到后端堆栈的顶部
| |
|A|
|C|
|A|
___
但我想恢复A
并摧毁它上面的所有碎片(如果有的话)。实际上,我只是喜欢默认的后台堆栈行为。
我该如何做到这一点?
预期:(应恢复A
并销毁顶部碎片)
| |
| |
| |
|A|
___
编辑:(由A - C建议)
这是我尝试的代码:
private void selectItem(int position) {
Fragment problemSearch = null, problemStatistics = null;
FragmentManager manager = getSupportFragmentManager();
FragmentTransaction ft = manager.beginTransaction();
String backStateName = null;
Fragment fragmentName = null;
boolean fragmentPopped = false;
switch (position) {
case 0:
fragmentName = profile;
break;
case 1:
fragmentName = submissionStatistics;
break;
case 2:
fragmentName = solvedProblemLevel;
break;
case 3:
fragmentName = latestSubmissions;
break;
case 4:
fragmentName = CPExercise;
break;
case 5:
Bundle bundle = new Bundle();
bundle.putInt("problem_no", problemNo);
problemSearch = new ProblemWebView();
problemSearch.setArguments(bundle);
fragmentName = problemSearch;
break;
case 6:
fragmentName = rankList;
break;
case 7:
fragmentName = liveSubmissions;
break;
case 8:
Bundle bundles = new Bundle();
bundles.putInt("problem_no", problemNo);
problemStatistics = new ProblemStatistics();
problemStatistics.setArguments(bundles);
fragmentName = problemStatistics;
default:
break;
}
backStateName = fragmentName.getClass().getName();
fragmentPopped = manager.popBackStackImmediate(backStateName, 0);
if (!fragmentPopped) {
ft.replace(R.id.content_frame, fragmentName);
}
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
ft.addToBackStack(backStateName);
ft.commit();
// I am using drawer layout
mDrawerList.setItemChecked(position, true);
setTitle(title[position]);
mDrawerLayout.closeDrawer(mDrawerList);
}
问题是,当我启动A
然后B
,然后按'后退',B
被删除,A
恢复。然后第二次按'后退'应退出应用程序。但是它显示一个空白窗口,我必须再次按回来关闭它。
此外,当我发射A
,然后B
,然后C
,然后B
再次...
预期:
| |
| |
|B|
|A|
___
实际:
| |
|B|
|B|
|A|
___
我应该用任何自定义覆盖onBackPressed()
还是我错过了什么?
读取documentation,有一种方法可以根据事务名称或commit提供的id弹出后台堆栈。使用该名称可能更容易,因为它不需要跟踪可能改变的数字并加强“唯一的后栈条目”逻辑。
由于每个Fragment
只需要一个后向堆栈条目,因此将后面的状态名称设为Fragment的类名(通过getClass().getName()
)。然后当替换Fragment
时,使用popBackStackImmediate()
方法。如果返回true,则表示后端堆栈中存在Fragment的实例。如果没有,实际执行Fragment替换逻辑。
private void replaceFragment (Fragment fragment){
String backStateName = fragment.getClass().getName();
FragmentManager manager = getSupportFragmentManager();
boolean fragmentPopped = manager.popBackStackImmediate (backStateName, 0);
if (!fragmentPopped){ //fragment not in back stack, create it.
FragmentTransaction ft = manager.beginTransaction();
ft.replace(R.id.content_frame, fragment);
ft.addToBackStack(backStateName);
ft.commit();
}
}
编辑
问题是 - 当我启动A然后启动B,然后按回按钮,B被移除并且A被恢复。并再次按下后退按钮应该退出应用程序。但它显示一个空白窗口,需要另一个按下来关闭它。
这是因为FragmentTransaction
被添加到后栈以确保我们可以稍后将片段弹出。一个快速解决方法是覆盖onBackPressed()
并完成活动,如果后面的堆栈只包含1个Fragment
@Override
public void onBackPressed(){
if (getSupportFragmentManager().getBackStackEntryCount() == 1){
finish();
}
else {
super.onBackPressed();
}
}
关于重复的后备栈条目,如果片段尚未弹出,则替换片段的条件语句明显不同于我的原始代码片段。无论后备堆栈是否弹出,您正在做的是添加到后台堆栈。
这样的东西应该更接近你想要的东西:
private void replaceFragment (Fragment fragment){
String backStateName = fragment.getClass().getName();
String fragmentTag = backStateName;
FragmentManager manager = getSupportFragmentManager();
boolean fragmentPopped = manager.popBackStackImmediate (backStateName, 0);
if (!fragmentPopped && manager.findFragmentByTag(fragmentTag) == null){ //fragment not in back stack, create it.
FragmentTransaction ft = manager.beginTransaction();
ft.replace(R.id.content_frame, fragment, fragmentTag);
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
ft.addToBackStack(backStateName);
ft.commit();
}
}
条件有点改变,因为选择相同的片段,而它可见也导致重复条目。
执行:
我强烈建议不要像你在代码中那样分开更新的replaceFragment()
方法。所有逻辑都包含在此方法中,并且移动部件可能会导致问题。
这意味着您应该将更新的replaceFragment()
方法复制到您的班级然后更改
backStateName = fragmentName.getClass().getName();
fragmentPopped = manager.popBackStackImmediate(backStateName, 0);
if (!fragmentPopped) {
ft.replace(R.id.content_frame, fragmentName);
}
ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
ft.addToBackStack(backStateName);
ft.commit();
所以很简单
replaceFragment (fragmentName);
编辑#2
要在后台堆栈更改时更新抽屉,请创建一个在片段中接受的方法并比较类名称。如果匹配,请更改标题和选择。如果有一个有效的片段,还要添加一个OnBackStackChangedListener
并让它调用你的更新方法。
例如,在Activity的onCreate()
中,添加
getSupportFragmentManager().addOnBackStackChangedListener(new OnBackStackChangedListener() {
@Override
public void onBackStackChanged() {
Fragment f = getSupportFragmentManager().findFragmentById(R.id.content_frame);
if (f != null){
updateTitleAndDrawer (f);
}
}
});
另一种方法:
private void updateTitleAndDrawer (Fragment fragment){
String fragClassName = fragment.getClass().getName();
if (fragClassName.equals(A.class.getName())){
setTitle ("A");
//set selected item position, etc
}
else if (fragClassName.equals(B.class.getName())){
setTitle ("B");
//set selected item position, etc
}
else if (fragClassName.equals(C.class.getName())){
setTitle ("C");
//set selected item position, etc
}
}
现在,每当后台堆栈发生变化时,标题和检查位置将反映可见的Fragment
。
我认为这种方法可以解决你的问题:
public static void attachFragment ( int fragmentHolderLayoutId, Fragment fragment, Context context, String tag ) {
FragmentManager manager = ( (AppCompatActivity) context ).getSupportFragmentManager ();
FragmentTransaction ft = manager.beginTransaction ();
if (manager.findFragmentByTag ( tag ) == null) { // No fragment in backStack with same tag..
ft.add ( fragmentHolderLayoutId, fragment, tag );
ft.addToBackStack ( tag );
ft.commit ();
}
else {
ft.show ( manager.findFragmentByTag ( tag ) ).commit ();
}
}
最初发布在This Question
第1步:使用您的活动类实现接口
public class AuthenticatedMainActivity extends Activity implements FragmentManager.OnBackStackChangedListener{
@Override
protected void onCreate(Bundle savedInstanceState) {
.............
FragmentManager fragmentManager = getFragmentManager();
fragmentManager.beginTransaction().add(R.id.frame_container,fragment, "First").addToBackStack(null).commit();
}
private void switchFragment(Fragment fragment){
FragmentManager fragmentManager = getFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.frame_container, fragment).addToBackStack("Tag").commit();
}
@Override
public void onBackStackChanged() {
FragmentManager fragmentManager = getFragmentManager();
System.out.println("@Class: SummaryUser : onBackStackChanged "
+ fragmentManager.getBackStackEntryCount());
int count = fragmentManager.getBackStackEntryCount();
// when a fragment come from another the status will be zero
if(count == 0){
System.out.println("again loading user data");
// reload the page if user saved the profile data
if(!objPublicDelegate.checkNetworkStatus()){
objPublicDelegate.showAlertDialog("Warning"
, "Please check your internet connection");
}else {
objLoadingDialog.show("Refreshing data...");
mNetworkMaster.runUserSummaryAsync();
}
// IMPORTANT: remove the current fragment from stack to avoid new instance
fragmentManager.removeOnBackStackChangedListener(this);
}// end if
}
}
第2步:当您调用另一个片段时,添加以下方法:
String backStateName = this.getClass().getName();
FragmentManager fragmentManager = getFragmentManager();
fragmentManager.addOnBackStackChangedListener(this);
Fragment fragmentGraph = new GraphFragment();
Bundle bundle = new Bundle();
bundle.putString("graphTag", view.getTag().toString());
fragmentGraph.setArguments(bundle);
fragmentManager.beginTransaction()
.replace(R.id.content_frame, fragmentGraph)
.addToBackStack(backStateName)
.commit();
getFragmentManager().addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
@Override
public void onBackStackChanged() {
if(getFragmentManager().getBackStackEntryCount()==0) {
onResume();
}
}
});
更容易的解决方案将改变这条线
ft.replace(R.id.content_frame, A);
到ft.add(R.id.content_frame, A);
在你的XML布局中,请使用
android:background="@color/white"
android:clickable="true"
android:focusable="true"
Clickable
表示它可以被指针设备点击或被触摸设备点击。
Focusable
意味着它可以从键盘等输入设备获得焦点。键盘等输入设备无法根据输入本身决定将输入事件发送到哪个视图,因此将它们发送到具有焦点的视图。
我知道回答这个问题已经很晚了,但我自己解决了这个问题,并且认为值得与大家分享
public void replaceFragment(BaseFragment fragment) {
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
final FragmentManager fManager = getSupportFragmentManager();
BaseFragment fragm = (BaseFragment) fManager.findFragmentByTag(fragment.getFragmentTag());
transaction.setCustomAnimations(R.anim.enter_from_right, R.anim.exit_to_left, R.anim.enter_from_left, R.anim.exit_to_right);
if (fragm == null) { //here fragment is not available in the stack
transaction.replace(R.id.container, fragment, fragment.getFragmentTag());
transaction.addToBackStack(fragment.getFragmentTag());
} else {
//fragment was found in the stack , now we can reuse the fragment
// please do not add in back stack else it will add transaction in back stack
transaction.replace(R.id.container, fragm, fragm.getFragmentTag());
}
transaction.commit();
}
并在onBackPressed()
@Override
public void onBackPressed() {
if(getSupportFragmentManager().getBackStackEntryCount()>1){
super.onBackPressed();
}else{
finish();
}
}