Fragments之间的交互(实现参数传递)
日常开发中，通常Fragments之间可能需要交互，比如基于用户事件改变Fragment的内容。所有Fragment之间的交互需要通过他们关联的Activity，两个Fragment之间不应该直接交互。
采用接口回调的方式来实现Fragments之间的交互，大致分为四步：
1.定义一个接口
- 为了让Fragment与Activity交互，可以在Fragment类中定义一个接口，并在Activity中实现。Fragment在它们的生命周期的onAttach()方法中获取接口的实现，然后调用接口的方法来与Activity交互。
定义接口的代码如下：
public class ListFragment extends Fragment implements AdapterView.OnItemClickListener {
private ListView mListView;
private ListAdapter mAdapter;
private List<String> mData;
public ListFragment() {
// Required empty public constructor
}
public static ListFragment newInstance(String type) {
Bundle args = new Bundle();
args.putString("type", type);
ListFragment fragment = new ListFragment();
fragment.setArguments(args);
return fragment;
}
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (mData == null) {
mData = new ArrayList<>();
}
loadData();
}
private void loadData() {
for (int i = 0; i < 10; i++) {
mData.add("Item" + i);
}
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View rootView = inflater.inflate(R.layout.fragment_list, container, false);
mListView = (ListView) rootView.findViewById(R.id.list_view);
mAdapter = new ListAdapter(getActivity(), mData);
mListView.setAdapter(mAdapter);
mListView.setOnItemClickListener(this);
return rootView;
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
// This makes sure that the container activity has implemented
// the callback interface. If not, it throws an exception
try {
mOnListItemSelectedListener = (OnListItemSelectedListener) context;
} catch (ClassCastException e) {
throw new ClassCastException(context.toString()
+ " must implement OnListItemSelectedListener");
}
}
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
mOnListItemSelectedListener.onListItemSelected(position);
}
private OnListItemSelectedListener mOnListItemSelectedListener;
public interface OnListItemSelectedListener {
void onListItemSelected(int position);
}
/* ================适配器相关===============*/
public class ListAdapter extends BaseAdapter {
private List<String> mData;
private Context mContext;
public ListAdapter(Context context, List<String> data) {
this.mContext = context;
this.mData = data;
}
@Override
public int getCount() {
return mData.size() == 0 ? 0 : mData.size();
}
@Override
public Object getItem(int position) {
return mData == null ? null : mData.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) {
holder = new ViewHolder();
convertView = LayoutInflater.from(mContext).inflate(R.layout.item_list, parent, false);
holder.mTextView = (TextView) convertView.findViewById(R.id.text_view);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
String text = mData.get(position);
if (text != null && !"".equals(text)) {
holder.mTextView.setText(text);
}
return convertView;
}
public class ViewHolder {
TextView mTextView;
}
}
}
- 现在Fragment就可以通过OnListItemSelectedListener 接口实例的mOnListItemSelectedListener中的onListItemSelected()方法与Activity传递消息。
- 我这个例子实现的是在ListFragment中点击ListView的一个Item，把这个Item的position传递给DetailFragment，DetailFragment展示具体的信息，如新闻列表，点击Item之后进入新闻详情页。
- 当我们点击Item时，ListFragment用回调接口来传递事件给父Activity。
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
mOnListItemSelectedListener.onListItemSelected(position);
}
2.实现接口
- 为了接收回调事件，宿主Activity必须实现Fragment中定义的接口。
- MainActivity实现了ListFragment中的接口，如下代码：
public class MainActivity extends AppCompatActivity
implements ListFragment.OnListItemSelectedListener {
private static final String TAG = "MainActivity";
private ListFragment mListFragment;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mListFragment = ListFragment.newInstance("ListFragment");
ActivityUtil.addFragmentToActivity(getSupportFragmentManager(),
mListFragment, R.id.frame_container);
}
@Override
public void onListItemSelected(int position) {
Log.d(TAG, position + "");
Bundle args = new Bundle();
args.putInt("position",position);
DetailFragment fragment = DetailFragment.newInstance("DetailFragment");
fragment.setArguments(args);
ActivityUtil.addFragmentToActivity(getSupportFragmentManager(), fragment, R.id.frame_container);
}
}
3.传递消息给Fragment
- 宿主MainActivity中还包含了另外一个Fragment（DetailFragment），DetailFragment用来展示回调方法中指定Item的内容。在这种情况下，MainActivity可以把回调方法中接收到的position传递给DetailFragment。
@Override
public void onListItemSelected(int position) {
Log.d(TAG, position + "");
Bundle args = new Bundle();
args.putInt("position",position);
DetailFragment fragment = DetailFragment.newInstance("DetailFragment");
fragment.setArguments(args);
ActivityUtil.addFragmentToActivity(getSupportFragmentManager(), fragment, R.id.frame_container);
}
4.接收传递的参数
- 在DetailFragment中接收ListFragment传递的position参数
public class DetailFragment extends Fragment {
private TextView mTextView;
private Bundle args;
public DetailFragment() {
// Required empty public constructor
}
public static DetailFragment newInstance(String type) {
Bundle args = new Bundle();
args.putString("type", type);
DetailFragment fragment = new DetailFragment();
fragment.setArguments(args);
return fragment;
}
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
args = getArguments();//获取传递的参数
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View rootView = inflater.inflate(R.layout.fragment_detail, container, false);
mTextView = (TextView) rootView.findViewById(R.id.text_view);
mTextView.setText(args.get("position").toString());
return rootView;
}
}
这样就实现了两个Fragment之间的交互。其核心就是拥有同一个宿主Activity的Fragments利用接口回调的方式实现参数的传递。
博客地址：http://tonycheng93.github.io/
源码地址：https://github.com/tonycheng93/Fragment2Fragment