我希望RecyclerView中有Fragment。我正在使用https://developer.android.com/samples/RecyclerView/src/com.example.android.recyclerview/RecyclerViewFragment.html#l19中的RecyclerViewFragment.java，但我仍然得到例外。
这是代码。
RecyclerViewFragment.java
package com.example.narehh.todolist.Fragments;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.RadioButton;
import com.example.narehh.todolist.Adapters.TaskListAdapter;
import com.example.narehh.todolist.JavaClasses.Task;
import com.example.narehh.todolist.R;
import java.util.ArrayList;
/**
* Demonstrates the use of {@link RecyclerView} with a {@link LinearLayoutManager} and a
* {@link GridLayoutManager}.
*/
public class TaskListFragment extends Fragment {
private static final String TAG = "TaskListFragment";
private static final String KEY_LAYOUT_MANAGER = "layoutManager";
private static final int SPAN_COUNT = 2;
private static final int DATASET_COUNT = 60;
private enum LayoutManagerType {
GRID_LAYOUT_MANAGER,
LINEAR_LAYOUT_MANAGER
}
protected LayoutManagerType mCurrentLayoutManagerType;
protected RadioButton mLinearLayoutRadioButton;
protected RadioButton mGridLayoutRadioButton;
protected RecyclerView mRecyclerView;
protected TaskListAdapter mAdapter;
protected RecyclerView.LayoutManager mLayoutManager;
// protected String[] mDataset;
protected ArrayList<Task> mDataset;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Initialize dataset, this data would usually come from a local content provider or
// remote server.
initDataset();
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_task_list,container, false);
rootView.setTag(TAG);
mRecyclerView = (RecyclerView) rootView.findViewById(R.id.task_list_rv);
// LinearLayoutManager is used here, this will layout the elements in a similar fashion
// to the way ListView would layout elements. The RecyclerView.LayoutManager defines how
// elements are laid out.
mLayoutManager = new LinearLayoutManager(getActivity());
mCurrentLayoutManagerType = LayoutManagerType.LINEAR_LAYOUT_MANAGER;
if (savedInstanceState != null) {
// Restore saved layout manager type.
mCurrentLayoutManagerType = (LayoutManagerType) savedInstanceState
.getSerializable(KEY_LAYOUT_MANAGER);
}
setRecyclerViewLayoutManager(mCurrentLayoutManagerType);
mAdapter = new TaskListAdapter(mDataset);
// Set CustomAdapter as the adapter for RecyclerView.
mRecyclerView.setAdapter(mAdapter);
// mLinearLayoutRadioButton = (RadioButton) rootView.findViewById(R.id.linear_layout_rb);
// mLinearLayoutRadioButton.setOnClickListener(new View.OnClickListener() {
// @Override
// public void onClick(View v) {
// setRecyclerViewLayoutManager(LayoutManagerType.LINEAR_LAYOUT_MANAGER);
// }
// });
//
// mGridLayoutRadioButton = (RadioButton) rootView.findViewById(R.id.grid_layout_rb);
// mGridLayoutRadioButton.setOnClickListener(new View.OnClickListener() {
// @Override
// public void onClick(View v) {
// setRecyclerViewLayoutManager(LayoutManagerType.GRID_LAYOUT_MANAGER);
// }
// });
return rootView;
}
/**
* Set RecyclerView's LayoutManager to the one given.
*
* @param layoutManagerType Type of layout manager to switch to.
*/
public void setRecyclerViewLayoutManager(LayoutManagerType layoutManagerType) {
int scrollPosition = 0;
// If a layout manager has already been set, get current scroll position.
if (mRecyclerView.getLayoutManager() != null) {
scrollPosition = ((LinearLayoutManager) mRecyclerView.getLayoutManager())
.findFirstCompletelyVisibleItemPosition();
}
switch (layoutManagerType) {
case GRID_LAYOUT_MANAGER:
mLayoutManager = new GridLayoutManager(getActivity(), SPAN_COUNT);
mCurrentLayoutManagerType = LayoutManagerType.GRID_LAYOUT_MANAGER;
break;
case LINEAR_LAYOUT_MANAGER:
mLayoutManager = new LinearLayoutManager(getActivity());
mCurrentLayoutManagerType = LayoutManagerType.LINEAR_LAYOUT_MANAGER;
break;
default:
mLayoutManager = new LinearLayoutManager(getActivity());
mCurrentLayoutManagerType = LayoutManagerType.LINEAR_LAYOUT_MANAGER;
}
mRecyclerView.setLayoutManager(mLayoutManager);
mRecyclerView.scrollToPosition(scrollPosition);
}
@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
// Save currently selected layout manager.
savedInstanceState.putSerializable(KEY_LAYOUT_MANAGER, mCurrentLayoutManagerType);
super.onSaveInstanceState(savedInstanceState);
}
/**
* Generates Strings for RecyclerView's adapter. This data would usually come
* from a local content provider or remote server.
*/
private void initDataset() {
// mDataset = new String[DATASET_COUNT];
// for (int i = 0; i < DATASET_COUNT; i++) {
// mDataset[i] = "This is element #" + i;
// }
mDataset = new ArrayList<Task>();
Task task1 = new Task(0, "task1", "01-09-2016", "10:10");
Task task2 = new Task(0, "task2", "01-09-2016", "10:10");
Task task3 = new Task(0, "task3", "01-09-2016", "10:10");
mDataset.add(task1);
mDataset.add(task2);
mDataset.add(task3);
}
}
和适配器：
package com.example.narehh.todolist.Adapters;
import android.support.v7.widget.RecyclerView;
import android.view.View;
import android.view.ViewGroup;
import android.widget.CheckBox;
import android.widget.TextView;
import com.example.narehh.todolist.JavaClasses.Task;
import com.example.narehh.todolist.R;
import java.util.ArrayList;
import java.util.List;
/**
* Created by Narehh on 7/10/2016.
*/
public class TaskListAdapter extends RecyclerView.Adapter<TaskListAdapter.TaskViewHolder> {
private ArrayList<Task> taskList = new ArrayList<Task>();
public TaskListAdapter(ArrayList<Task> taskList) {
this.taskList = taskList;
}
@Override
public TaskListAdapter.TaskViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
return null;
}
@Override
public void onBindViewHolder(TaskViewHolder holder, int position) {
Task task = taskList.get(position);
holder.title.setText(task.getName());
holder.date.setText(task.getDate() + task.getTime());
holder.isDone.setChecked(false);
}
@Override
public int getItemCount() {
return taskList.size();
}
public static class TaskViewHolder extends RecyclerView.ViewHolder {
protected TextView title;
protected TextView date;
protected CheckBox isDone;
public TaskViewHolder(View v) {
super(v);
title = (TextView) v.findViewById(R.id.title);
date = (TextView) v.findViewById(R.id.date);
isDone = (CheckBox) v.findViewById(R.id.isDone);
}
}
}
我得到了这个例外
FATAL EXCEPTION: main
Process: com.example.narehh.todolist, PID: 16871
java.lang.NullPointerException
at android.support.v7.widget.RecyclerView$Adapter.createViewHolder(RecyclerView.java:5780)
at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5003)
at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:4913)
at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2029)
at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1414)
at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1377)
at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:578)
at android.support.v7.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:3260)
at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:3069)
at android.support.v7.widget.RecyclerView.onLayout(RecyclerView.java:3518)
at android.view.View.layout(View.java:15781)
at android.view.ViewGroup.layout(ViewGroup.java:4884)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:15781)
at android.view.ViewGroup.layout(ViewGroup.java:4884)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:15781)
at android.view.ViewGroup.layout(ViewGroup.java:4884)
at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1055)
at android.view.View.layout(View.java:15781)
at android.view.ViewGroup.layout(ViewGroup.java:4884)
at android.support.design.widget.HeaderScrollingViewBehavior.layoutChild(HeaderScrollingViewBehavior.java:120)
at android.support.design.widget.ViewOffsetBehavior.onLayoutChild(ViewOffsetBehavior.java:42)
at android.support.design.widget.AppBarLayout$ScrollingViewBehavior.onLayoutChild(AppBarLayout.java:1319)
at android.support.design.widget.CoordinatorLayout.onLayout(CoordinatorLayout.java:815)
at android.view.View.layout(View.java:15781)
at android.view.ViewGroup.layout(ViewGroup.java:4884)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:15781)
at android.view.ViewGroup.layout(ViewGroup.java:4884)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1677)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1531)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1440)
at android.view.View.layout(View.java:15781)
at android.view.ViewGroup.layout(ViewGroup.java:4884)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:15781)
at android.view.ViewGroup.layout(ViewGroup.java:4884)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1677)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1531)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1440)
at android.view.View.layout(View.java:15781)
at android.view.ViewGroup.layout(ViewGroup.java:4884)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:15781)
at android.view.ViewGroup.layout(ViewGroup.java:4884)
at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2361)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2074)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1256)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6658)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:813)
at android.view.Choreographer.doCallbacks(Choreographer.java:613)
at android.view.Choreographer.doFrame(Choreographer.java:583)
你有过这种问题吗？
答案 0 :(得分：1)
错误是因为您没有返回任何视图
首先在onCreateViewHolder
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.your_individual_layout_name, null);
final TaskViewHolder holder = new TaskViewHolder(view);
// this is where the each item is inflated.
return holder;
这将解决问题..
答案 1 :(得分：1)
你不应该从oncreateviewholder（）返回null，你应该总是返回你的查看者对象，该对象已经为你的recyclerview列表的每行增加了视图。