[英]Fragment Backstack
嗨,我有一个活动和三个片段。 当我替换我的第一个片段时,我将它添加到backstack中。
FragmentTransaction fragmentTransaction = getFragmentManager()
.beginTransaction();
fragmentTransaction.replace(R.id.authentication_parent0_linear,
new LoginFragment(), LOGINTAG);
fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();
但是当我在另外两个片段之间移动时,我没有将它们添加到backstack中。所以每当我从其他两个片段按回来时,我需要回到第一个片段。当我删除第一个片段并添加第二个片段或删除时它工作正常首先添加第三个,即当我按下时,我将回到第一个片段。 但是当我在这两个片段之间导航时,会删除第二个并添加第三个或删除第三个并添加第二个等。 在那个例子,当我按下我退出应用程序并且backstackcount显示为零但是我第一次删除第一个片段时将其存储在backstack中。
getFragmentManager()
.beginTransaction()
.replace(R.id.authentication_parent0_linear,
new SignupFragment(), SIGNUPTAG).commit();
所以我的问题是片段backstack会在提交之间重置。 如果是这样,我怎样才能第一次在后台堆叠中获取存储的片段
实现你想要的最好方法是不使用fragment的backstack。
addToBackStack()
在实例字段mLoginFragment中保留第一个片段LoginFragment
引用。 添加第一个片段将如下所示(可能在activity的onCreate()
:
FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction(); mLoginFragment = new LoginFragment(); fragmentTransaction.replace(R.id.authentication_parent0_linear, mLoginFragment, LOGINTAG); fragmentTransaction.commit();
在您的活动中重写onBackPressed()
方法如下:
@Override public void onBackPressed() { Fragment fr = getFragmentManager().findFragmentById(R.id.authentication_parent0_linear); // chek that mLoginFragment!=null, basically this should never happen! if (fr == mLoginFragment) { super.onBackPressed(); } else { FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction(); fragmentTransaction.replace(R.id.authentication_parent0_linear, mLoginFragment, LOGINTAG); fragmentTransaction.commit(); } }
使用背板可以通过一种麻烦的方式来达到预期的效果。 方法如下:
addToBAckStack()
addToBackStack()
当从B更深地导航到C等时,在事务之前调用popBackStack()
。 可以在SO上找到它的说明。 像这样:
getFragmentManager().popBackStack(); FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction(); fragmentTransaction.replace(R.id.authentication_parent0_linear, new FragmentC(), "whatever"); fragmentTransaction.addToBackStack(null); fragmentTransaction.commit();
片段管理器允许您将名称(或TAG)放在给定状态。 如果将相同的名称传递给popBackStack,它将弹出状态直到达到该状态。 例如
// Add initial fragment
getFragmentManager()
.beginTransaction();
.replace(R.id.authentication_parent0_linear, new LoginFragment());
.addToBackStack(TAG_FIRST_FRAGMENT_STATE) // The key is not passing null here
.commit();
// Add other fragments like such
getFragmentManager()
.beginTransaction();
.replace(R.id.authentication_parent0_linear, new SignupFragment());
.addToBackStack(null)
.commit();
// On back press
@Override
public void onBackPressed() {
FragmentManager fragmentManager = getFragmentManager();
if (fragmentManager.getBackStackEntryCount() > 1) {
fragmentManager.popBackStack(TAG_FIRST_FRAGMENT_STATE, 0);
} else {
super.onBackPress();
}
}
我最终想通了。 基于Kirill K答案
public class MainActivity extends Activity implements OnClickAuthentication,
LoginInterface, SignupInterface {
FragmentManager fragmentManager;
FragmentTransaction fragmentTransaction;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
fragmentManager = getFragmentManager();
Fragment fragment = fragmentManager.findFragmentByTag("one");
if (fragment == null) {
fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction
.replace(R.id.relative, new OneFragment(), "one");
fragmentTransaction.commit();
}
}
@Override
public void onClickAuthButton(int flag) {
if (flag == 2) {
fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction
.replace(R.id.relative, new TwoFragment(), "two");
fragmentTransaction.commit();
} else {
fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.relative, new ThreeFragment(),
"three");
fragmentTransaction.commit();
}
}
@Override
public void switchToSignup() {
fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction
.replace(R.id.relative, new ThreeFragment(), "three");
fragmentTransaction.commit();
}
@Override
public void switchToLogin() {
fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.relative, new TwoFragment(), "two");
fragmentTransaction.commit();
}
@Override
public void onBackPressed() {
Fragment twoFragment = fragmentManager.findFragmentByTag("two");
Fragment threeFragment = fragmentManager.findFragmentByTag("three");
if ((twoFragment != null && twoFragment.isVisible())
|| (threeFragment != null && threeFragment.isVisible())) {
fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction
.replace(R.id.relative, new OneFragment(), "one");
fragmentTransaction.commit();
} else {
super.onBackPressed();
}
}
}
我这样做了
FragmentManager fm = getFragmentManager();
fm.beginTransaction().replace(R.id.content_frame , new main_fragment()).commit();
void replaceFragment (Fragment fragment) {
Fragment current = fm.findFragmentById(R.id.content_frame);
//Check if that frag is already opened
if (!current.getClass().equals(fragment.getClass())) {
String backStateName = fragment.getClass().getName();
boolean fragmentPopped = fm.popBackStackImmediate(backStateName, 0);
if (!fragmentPopped) {
//fragment is not in back stack,so add it.
FragmentTransaction ft = fm.beginTransaction();
ft.replace(R.id.content_frame, fragment);
ft.addToBackStack(backStateName);
ft.commit();
}
}
else {
//if fragmentPopped is true then it will auto pop up the fragment
//so we dnt have to do anything here
}
}
replaceFragment(new yourfragment());
public void onBackPressed() {
int backStackEntryCount = fm.getBackStackEntryCount();
if (backStackEntryCount == 0) {
new AlertDialog.Builder(this)
.setIcon(android.R.drawable.ic_dialog_alert)
.setTitle("Closing Activity")
.setMessage("Are you sure you want to close this Application?")
.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
finish();
System.exit(0);
}
})
.setNegativeButton("No", null)
.setOnCancelListener(new DialogInterface.OnCancelListener() {
@Override
public void onCancel(DialogInterface dialogInterface) {
//backpress over alert dialog
finish();
System.exit(0);
}
})
.show();
} else {
super.onBackPressed();
}
}
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