我的原始答案建议使用add 而不是replace 进行片段交易。从那以后，我了解到在这种情况下可以使用任何一种。有关差异的更多信息，请参阅this、this 和 this
由于我的添加/替换想法没有根据，我已将答案更改为简单的片段教程。一个片段从一个活动膨胀。我已经包含了 Fragment 到 Activity 通信的代码（OPs 问题的原因），但是如果不需要的话，可以删除哪些内容。 Activity 中唯一要做的事情是启动 Fragment，然后从该 Fragment 接收消息。 Fragment 有一个按钮，可以将消息发送回 Activity。然后将记录该消息。
在这两个类中，如果不需要从 Fragment 到 Activity 的通信，请删除任何标记为 TODO 的内容：
// this is what controls whether you use a Fragment from the support library
import android.support.v4.app.FragmentManager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
public class SimpleActivity extends AppCompatActivity
// TODO: delete "implements SimpleFragment.OnFragmentInteractionListener" from this
// line (leave the '{')
implements SimpleFragment.OnFragmentInteractionListener {
private static final String TAG = SimpleActivity.class.getSimpleName();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_simple);
SimpleFragment fragment = new SimpleFragment();
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction()
.add(R.id.fragment_container, fragment)
.commit();
}
// TODO: this entire method can be deleted
@Override
public void onFragmentInteraction(String message) {
// This is where you can act on the message from the Fragment. You would do
// things that are done from an Activity or you may pass the message on
// to another Fragment.
Log.d(TAG, message);
}
}
大部分导入语句都没有显示，我留下这个是为了表示使用支持库
import android.support.v4.app.Fragment;
public class SimpleFragment extends Fragment {
private OnFragmentInteractionListener mListener; // TODO: delete this line
public SimpleFragment() {
// Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View rootView = inflater.inflate(R.layout.fragment_simple, container, false);
Button button = (Button)rootView.findViewById(R.id.msg_button);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
// TODO: delete these 3 lines, do something else with the button click
if (mListener != null) {
mListener.onFragmentInteraction("Message from Fragment");
}
}
});
return rootView;
}
// TODO: this entire method can be deleted
@Override
public void onAttach(Context context) {
super.onAttach(context);
if (context instanceof OnFragmentInteractionListener) {
mListener = (OnFragmentInteractionListener) context;
} else {
throw new RuntimeException(context.toString()
+ " must implement OnFragmentInteractionListener");
}
}
// TODO: this entire method can be deleted
@Override
public void onDetach() {
super.onDetach();
mListener = null;
}
// TODO: this entire method can be deleted
public interface OnFragmentInteractionListener {
void onFragmentInteraction(String message);
}
}
现在是布局文件。第一个activity_simple.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<FrameLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/fragment_container"
>
</FrameLayout>
</android.support.constraint.ConstraintLayout>
然后是fragment_simple.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:text="Info to Activity"
android:id="@+id/msg_button"
/>
</RelativeLayout>
这是一个非常基本的示例。 Here 是更全面的 Fragment 使用指南。