如何在我的活动中动态添加片段？

Question

我使用的是Android，它实现了片段类的所有功能。我得到以下运行时异常：

must implement OnFragmentInteractionListener

这是我的代码，我已经在我的主要活动中实现了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");
        }
    }
}

片段类和main活动的其余方法也在默认情况下实现。我还用FrameLayout在main_activity.xmlfile and also assignedandroid: is `中更改了FrameLayout，这是很好的参考。我的密码怎么了？

Answer 1

要与您的BlankFragment对象交互，我将使用Android支持文档中推荐的以下方法--我相信这是您正在尝试实现的，而且它将适合于BlankFragment对象由MainActivity托管

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();
    }
}

为了与片段进行通信，您将执行以下操作：

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

然后，您可以调用任何与fragment关联的方法。

如果相反(从片段到活动之间的通信)，则需要在BlankFragment中执行以下操作，以便与父Activity形成链接

//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");
        }
    }

您可能已经忘记了这最后一步，这可以解释您的错误。然后，您可以使用：

mCallback.onFragmentInteraction(uri);

与MainActivity通信

Answer 2

这对我有用，我刚刚在这里分享了它，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。