Question

我将滑块菜单displayview方法设为：

private void displayView(int position) {
                // update the main content by replacing fragments
                Fragment fragment = null;
                switch (position) {
                    case 0:
                        fragment = new HomeFragment();

                    FragmentManager fm = getSupportFragmentManager();
                    String tag = fragment.getTag(); // instance method of a to get a tag

                    FragmentTransaction ft = fm.beginTransaction();

                    ft.replace(R.id.frame_container, fragment, tag);
                    ft.addToBackStack(tag);
                    ft.commit();

                    default:
                        break;
                }

                if (fragment != null) {
                    FragmentManager fragmentManager = getFragmentManager();
                    fragmentManager.beginTransaction()
                            .replace(R.id.frame_container, fragment).commit();

                    // update selected item and title, then close the drawer
                    drawerListView.setItemChecked(position, true);
                    drawerListView.setSelection(position);
                    setTitle(navMenuTitles[position]);
                    drawer.closeDrawer(drawerListView);
                } else {
                    // error in creating fragment
                    Log.e("MainActivity", "Error in creating fragment");
                }
            }

我有一个名为home_fragment的片段，其后面的代码是HomeFragment.java

当我点击这个片段时，它首先工作正常，但是在索引0的侧板菜单上单击下一步时出现错误：

Attempt to write to field 'int android.support.v4.app.Fragment.mNextAnim' on a null object reference

我做错了什么？感谢。

这是我遇到错误的地方：

case OP_REMOVE: {
                    Fragment f = op.fragment;
                    f.mNextAnim = exitAnim;
                    mManager.removeFragment(f, transition, transitionStyle);
                } break;

此代码存在于BackStackRecord.java

中

Answer 1

你不应该打电话给container.removeAllViewsInLayout()。

FragmentManager将在您调用FragmentTransaction.replace()时处理容器上的所有视图操作，包括删除当前片段视图。您可能会收到错误，因为FragmentManager希望片段的视图位于容器中，但您已将其删除。

所有你需要的是：

        private void displayView(int position) {
            // update the main content by replacing fragments
            Fragment fragment = null;
            switch (position) {
                case 0:
                    fragment = new HomeFragment();
                    break;
                case 1:
                    // set fragment to other nav target
                    fragment = ...
                    break;
                .
                .
                .
                default:
                    break;
            }

            if (fragment != null) {
                FragmentManager fragmentManager = getSupportFragmentManager();
                fragmentManager.beginTransaction()
                        .replace(R.id.frame_container, fragment).commit();

                // update selected item and title, then close the drawer
                drawerListView.setItemChecked(position, true);
                drawerListView.setSelection(position);
                setTitle(navMenuTitles[position]);
                drawer.closeDrawer(drawerListView);
            } else {
                // error in creating fragment
                Log.e("MainActivity", "Error in creating fragment");
            }
        }

此外，我注意到您正在使用getFragmentManager()。请检查您的课程输入，并确保您有正确的电话。

如果HomeFragment延伸android.app.Fragment，请使用getFragmentManager()。
如果HomeFragment延伸android.support.v4.app.Fragment，请使用getSupportFragmentManager()。

从导航抽屉切换Android片段会导致应用退出

1 个答案: