[英]Display a RecyclerView in Fragment
我正在 Android Lollipop 中试用新的RecyclerView
,但被卡住了。
我正在尝试接收一个列表,在一个Fragment
,在图标的右侧有一个图标和一个TextView
。
我发现了这个关于如何设置RecyclerView
很棒的教程。 我遵循了每一点,只更改了item_layout.xml
以满足我的需要。
该项目构建时没有任何错误,但是当它在我的设备上启动时,我收到此错误:
java.lang.RuntimeException:无法启动活动 ComponentInfo{com.fredrikaldgard.materialcolors/com.fredikaldgard.materialcolors.MainActivity}:java.lang.NullPointerException:尝试调用虚拟方法 'void android.support.v7.widget.RecyclerView。空对象引用上的 setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)'
我试图用谷歌搜索这个问题,但我对 Android 开发非常业余。
这是我的MainActivity
:
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// 1. get a reference to recyclerView
RecyclerView recyclerView = (RecyclerView) findViewById(R.id.list);
// 2. set layoutManger
recyclerView.setLayoutManager(new LinearLayoutManager(this));
// this is data fro recycler view
ItemData itemsData[] = { new ItemData("Indigo",R.drawable.circle),
new ItemData("Red",R.drawable.color_ic_launcher),
new ItemData("Blue",R.drawable.indigo),
new ItemData("Green",R.drawable.circle),
new ItemData("Amber",R.drawable.color_ic_launcher),
new ItemData("Deep Orange",R.drawable.indigo)};
// 3. create an adapter
MyAdapter mAdapter = new MyAdapter(itemsData);
// 4. set adapter
recyclerView.setAdapter(mAdapter);
// 5. set item animator to DefaultAnimator
recyclerView.setItemAnimator(new DefaultItemAnimator());
还有我的MyAdapter
:
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
private ItemData[] itemsData;
public MyAdapter(ItemData[] itemsData) {
this.itemsData = itemsData;
}
// Create new views (invoked by the layout manager)
@Override
public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup parent,
int viewType) {
// create a new view
View itemLayoutView = LayoutInflater.from(parent.getContext())
.inflate(R.layout.item_layout, null);
// create ViewHolder
ViewHolder viewHolder = new ViewHolder(itemLayoutView);
return viewHolder;
}
// Replace the contents of a view (invoked by the layout manager)
@Override
public void onBindViewHolder(ViewHolder viewHolder, int position) {
// - get data from your itemsData at this position
// - replace the contents of the view with that itemsData
viewHolder.txtViewTitle.setText(itemsData[position].getTitle());
viewHolder.imgViewIcon.setImageResource(itemsData[position].getImageUrl());
}
// inner class to hold a reference to each item of RecyclerView
public static class ViewHolder extends RecyclerView.ViewHolder {
public TextView txtViewTitle;
public ImageView imgViewIcon;
public ViewHolder(View itemLayoutView) {
super(itemLayoutView);
txtViewTitle = (TextView) itemLayoutView.findViewById(R.id.item_title);
imgViewIcon = (ImageView) itemLayoutView.findViewById(R.id.item_icon);
}
}
// Return the size of your itemsData (invoked by the layout manager)
@Override
public int getItemCount() {
return itemsData.length;
}
}
编辑:这是Fragment
public class ColorsFragment extends Fragment {
public ColorsFragment(){}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_colors, container, false);
return rootView;
}
}
可能出了什么问题?
这是前一段时间被问到的,但是根据@nacho_zona3 提供的答案以及之前使用片段的经验,问题是当您尝试使用findViewById()
方法在onCreate()
要解决此问题,请移动以下代码:
// 1. get a reference to recyclerView
RecyclerView recyclerView = (RecyclerView) findViewById(R.id.list);
// 2. set layoutManger
recyclerView.setLayoutManager(new LinearLayoutManager(this));
// this is data from recycler view
ItemData itemsData[] = { new ItemData("Indigo",R.drawable.circle),
new ItemData("Red",R.drawable.color_ic_launcher),
new ItemData("Blue",R.drawable.indigo),
new ItemData("Green",R.drawable.circle),
new ItemData("Amber",R.drawable.color_ic_launcher),
new ItemData("Deep Orange",R.drawable.indigo)};
// 3. create an adapter
MyAdapter mAdapter = new MyAdapter(itemsData);
// 4. set adapter
recyclerView.setAdapter(mAdapter);
// 5. set item animator to DefaultAnimator
recyclerView.setItemAnimator(new DefaultItemAnimator());
到您片段的onCreateView()
调用。 需要少量重构,因为从此方法调用的所有变量和方法都必须是静态的。 最终代码应如下所示:
public class ColorsFragment extends Fragment {
public ColorsFragment() {}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_colors, container, false);
// 1. get a reference to recyclerView
RecyclerView recyclerView = (RecyclerView) rootView.findViewById(R.id.list);
// 2. set layoutManger
recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
// this is data from recycler view
ItemData itemsData[] = {
new ItemData("Indigo", R.drawable.circle),
new ItemData("Red", R.drawable.color_ic_launcher),
new ItemData("Blue", R.drawable.indigo),
new ItemData("Green", R.drawable.circle),
new ItemData("Amber", R.drawable.color_ic_launcher),
new ItemData("Deep Orange", R.drawable.indigo)
};
// 3. create an adapter
MyAdapter mAdapter = new MyAdapter(itemsData);
// 4. set adapter
recyclerView.setAdapter(mAdapter);
// 5. set item animator to DefaultAnimator
recyclerView.setItemAnimator(new DefaultItemAnimator());
return rootView;
}
}
所以这里的主要事情是在任何你调用findViewById()
你都需要使用rootView.findViewById()
在使用该视图膨胀核心视图后,您应该在Fragment
检索RecyclerView
。 也许它找不到您的回收站,因为它不是 Activity 的一部分
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
final View view = inflater.inflate(R.layout.fragment_artist_tracks, container, false);
final FragmentActivity c = getActivity();
final RecyclerView recyclerView = (RecyclerView) view.findViewById(R.id.recyclerView);
LinearLayoutManager layoutManager = new LinearLayoutManager(c);
recyclerView.setLayoutManager(layoutManager);
new Thread(new Runnable() {
@Override
public void run() {
final RecyclerAdapter adapter = new RecyclerAdapter(c);
c.runOnUiThread(new Runnable() {
@Override
public void run() {
recyclerView.setAdapter(adapter);
}
});
}
}).start();
return view;
}
确保您有正确的布局,并且 RecyclerView id 在布局内。 否则,您将收到此错误。 我遇到了同样的问题,然后我注意到布局错误。
public class ColorsFragment extends Fragment {
public ColorsFragment() {}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
==> make sure you are getting the correct layout here. R.layout...
View rootView = inflater.inflate(R.layout.fragment_colors, container, false);
我遇到了同样的问题。 并在我使用此代码调用上下文时得到了解决方案。 我使用网格布局。 如果你使用另一个你可以改变。
recyclerView.setLayoutManager(new GridLayoutManager(getActivity(),1));
如果你有适配器要设置。 所以你可以遵循这个。 只需调用 getContext
adapter = new Adapter(getContext(), myModelList);
如果您要显示 Toast,请使用上面相同的内容
Toast.makeText(getContext(), "Error in "+e, Toast.LENGTH_SHORT).show();
希望这会奏效。
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