如何在我的活动中动态添加片段？

Question

我正在使用 Android Studio，它实现了片段类的所有功能。我收到以下运行时异常：

must implement OnFragmentInteractionListener

这是我的代码，我在主要活动中实现了OnFragmentInteractionListener。

主要活动：

public class MainActivity extends FragmentActivity implements BlankFragment.OnFragmentInteractionListener {
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        if (findViewById(R.id.fragment_container) != null) {
            BlankFragment fragment = new BlankFragment();
            android.support.v4.app.FragmentManager manager = getSupportFragmentManager();
            android.support.v4.app.FragmentTransaction ft = manager.beginTransaction();
            ft.add(R.id.fragment_container, fragment).commit();
        }
    @Override            
    public void onFragmentInteraction(Uri uri) {}

}

空白片段：

public class BlankFragment extends android.support.v4.app.Fragment {
    private OnFragmentInteractionListener mListener;
    public interface OnFragmentInteractionListener {
        public void onFragmentInteraction(Uri uri);
    }

    public void onAttach(Activity activity) {
        super.onAttach(activity);
        try {
            mListener = (OnFragmentInteractionListener) activity;
        } catch (ClassCastException e) {
            throw new ClassCastException(activity.toString()
                    + " must implement OnFragmentInteractionListener");
        }
    }
}

fragment class 和 main Activity 的其余方法也是默认实现的。我还在 main_activity.xmlfile and also assignedandroid:id` 中将 LinearLayout 和 FrameLayout 更改为引用良好的它。我的代码有什么问题？

Answer 1

要与您的BlankFragment 对象进行交互，我将使用Android Support Docs 中推荐的以下方法 - 我相信这是您想要实现的目标，并且适合您的BlankFragment 对象托管MainActivity:

public class MainActivity extends FragmentActivity implements BlankFragment.OnFragmentInteractionListener    {

private BlankFragment fragment = null;
private android.support.v4.app.FragmentManager manager = null;
private android.support.v4.app.FragmentTransaction ft;

public void onFragmentInteraction(Uri uri){
        Log.i("Tag", "onFragmentInteraction called");
    }

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    if (manager == null) manager = getSupportFragmentManager();            

    if(manager.findFragmentById(R.id.fragment_container) == null) {

        //If a fragment is not already loaded into your container, then add one...

        fragment = new BlankFragment();
        ft= manager.beginTransaction();
        ft.add(R.id.fragment_container,fragment).commit();
    }
}

为了与您的片段进行通信，您需要执行以下操作：

if(fragment == null) {
    fragment = (BlankFragment) manager.findFragmentById(R.id.fragment_container);
}

然后您可以调用与fragment 关联的任何方法

如果是相反的方式（从片段到活动的通信），那么您需要在BlankFragment 中执行以下操作，以形成与父级Activity 的链接：

//Class variable...
OnFragmentInteractionListener mCallback;

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    try {
        mCallback = (OnFragmentInteractionListener) activity;
            } catch (ClassCastException e) {
        throw new ClassCastException(activity.toString()
                + " must implement OnFragmentInteractionListener");
        }
    }

您可能忘记了最后一步，这可以解释您的错误。然后你会使用：

mCallback.onFragmentInteraction(uri);

与MainActivity交流

Answer 2

这对我有用，我只是在这里分享，你永远不知道它会帮助其他人。

getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container, fragment).commit();

只有一行代码。