Question

我无法确定导航栏中是否选择了某个标签。我正在尝试确定是否已选择成分选项卡。每次运行我的代码时，它都会返回一个空指针错误，因为mFragment为null且尚未实例化。

好的......我明白mFragment是null。我想这是我感到困惑的地方。比较片段时，您是在比较它们的内容还是对象本身？如果有人知道如何比较那些很棒的片段。先感谢您。这是代码：

public static class TabListener<T extends Fragment> implements ActionBar.TabListener {
    private final Activity mActivity;
    private final String mTag;
    private final Class<T> mClass;
    private final Bundle mArgs;
    private Bundle mTitleArgs;
    private Fragment mFragment;
    private IngredientCreation ingredientFrag;
    private FragmentTabControl controller;

    public TabListener(Activity activity, String tag, Class<T> clz) {
        this(activity, tag, clz, null);
    }

    public TabListener(Activity activity, String tag, Class<T> clz, Bundle args) {
        mActivity = activity;
        mTag = tag;
        mClass = clz;
        mArgs = args;

        // Check to see if we already have a fragment for this tab, probably
        // from a previously saved state.  If so, deactivate it, because our
        // initial state is that a tab isn't shown.
        mFragment = mActivity.getFragmentManager().findFragmentByTag(mTag);
        if (mFragment != null && !mFragment.isDetached()) {
            FragmentTransaction ft = mActivity.getFragmentManager().beginTransaction();
            ft.detach(mFragment);
            ft.commit();
        }
    }

    public void onTabSelected(Tab tab, FragmentTransaction ft) {
        ingredientFrag = (IngredientCreation) mActivity.getFragmentManager().findFragmentByTag("ingredients");

        if (mFragment.equals(ingredientFrag)) {

            System.out.println("got here");
            mFragment = Fragment.instantiate(mActivity, mClass.getName(), mTitleArgs);
            ft.add(android.R.id.content, mFragment, mTag);
        } else {
            ft.attach(mFragment);
        }
    }

Answer 1

ActionBar上的文档提供了一个很好的示例，说明如何正确创建Tab Listener。查看此链接以获得良好的实施。 http://developer.android.com/guide/topics/ui/actionbar.html

使用导航栏中的标签比较片段

1 个答案: