Question

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。

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，我不会将它们添加到backstack中。所以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时，它工作正常片段或删除第一个并添加第三个，即当我按回来时，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，但是当我第一次删除第一个片段时，我将它存储在后台中。

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

Answer 1

实现您想要的最佳方式是不使用片段的后台堆栈。

请勿在任何地方使用addToBackStack()

在实例字段mLoginFragment中保留第一个片段LoginFragment引用。添加您的第一个片段将如下所示（可能在活动中onCreate()：

  FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction();
  mLoginFragment = new LoginFragment();
  fragmentTransaction.replace(R.id.authentication_parent0_linear, mLoginFragment, LOGINTAG);
  fragmentTransaction.commit();

覆盖onBackPressed()方法，如下所示：

@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backstack有一种麻烦的方法可以达到预期的效果。方法如下：

在创建片段A时调用addToBAckStack()
从片段A导航到B或C，或导航到其他片段呼叫 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();

Answer 2

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();
    }
}

Answer 3

我最终想通了。基于Kirill K回答

    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();
    }
}

}

Answer 4

我这样做了

1。全局声明fragmentManager变量：

FragmentManager fm = getFragmentManager();

2.onCreate方法加载第一个片段而不使用backstack

fm.beginTransaction().replace(R.id.content_frame , new main_fragment()).commit();

3。现在，当你要添加新的片段然后创建一个方法，它将检查片段是否已经在backstack中，并且它将处理单击相同的片段事件（如果你在导航抽屉中使用frag）

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     
    }
}

4。现在只需将您的片段类传递给

replaceFragment(new yourfragment());

5。现在处理背压

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();
        }


    }

片段Backstack

4 个答案:

1。全局声明fragmentManager变量：

2.onCreate方法加载第一个片段而不使用backstack

3。现在，当你要添加新的片段然后创建一个方法，它将检查片段是否已经在backstack中，并且它将处理单击相同的片段事件（如果你在导航抽屉中使用frag）

4。现在只需将您的片段类传递给

5。现在处理背压

希望这会对你有所帮助