我试图在 RecyclerView 中选择视图时更改视图的颜色。我使用了本教程中的适配器：http : //www.android4devs.com/2014/12/how-to-make-material-design-navigation-drawer.html 并从答案中添加了 onClick 方法：https:// stackoverflow.com/a/27868923/3569225。这是我现在的代码：
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
private static final int TYPE_HEADER = 0; // Declaring Variable to Understand which View is being worked on
// IF the view under inflation and population is header or Item
private static final int TYPE_ITEM = 1;
private String mNavTitles[]; // String Array to store the passed titles Value from MainActivity.java
private int mIcons[]; // Int Array to store the passed icons resource value from MainActivity.java
private String name; //String Resource for header View Name
private int mSelectedPosition = 0;
private OnMyListItemClick mOnMainMenuClickListener = OnMyListItemClick.NULL;
// Creating a ViewHolder which extends the RecyclerView View Holder
// ViewHolder are used to to store the inflated views in order to recycle them
public static class ViewHolder extends RecyclerView.ViewHolder {
int Holderid;
TextView textView;
ImageView imageView;
TextView Name;
public ViewHolder(View itemView,int ViewType) { // Creating ViewHolder Constructor with View and viewType As a parameter
super(itemView);
// Here we set the appropriate view in accordance with the the view type as passed when the holder object is created
if(ViewType == TYPE_ITEM) {
textView = (TextView) itemView.findViewById(R.id.rowText); // Creating TextView object with the id of textView from item_row.xml
imageView = (ImageView) itemView.findViewById(R.id.rowIcon);// Creating ImageView object with the id of ImageView from item_row.xml
Holderid = 1; // setting holder id as 1 as the object being populated are of type item row
}
else{
Name = (TextView) itemView.findViewById(R.id.name); // Creating Text View object from header.xml for name
Holderid = 0; // Setting holder id = 0 as the object being populated are of type header view
}
}
}
public interface OnMyListItemClick {
OnMyListItemClick NULL = new OnMyListItemClick() {
@Override
public void onMyListItemClick(View itemView) {
}
};
void onMyListItemClick(View itemView);
}
MyAdapter(String Titles[],int Icons[],String Name){ // MyAdapter Constructor with titles and icons parameter
// titles, icons, name, email, profile pic are passed from the main activity as we
mNavTitles = Titles; //have seen earlier
mIcons = Icons;
name = Name;
//in adapter
}
//Below first we ovverride the method onCreateViewHolder which is called when the ViewHolder is
//Created, In this method we inflate the item_row.xml layout if the viewType is Type_ITEM or else we inflate header.xml
// if the viewType is TYPE_HEADER
// and pass it to the view holder
@Override
public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
if (viewType == TYPE_ITEM) {
View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.drawer_list_item,parent,false); //Inflating the layout
final ViewHolder vhItem = new ViewHolder(v,viewType); //Creating ViewHolder and passing the object of type view
v.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//here you set your current position from holder of clicked view
mSelectedPosition = ((ViewHolder) view.getTag()).getPosition();
//here you pass object from your list - item value which you clicked
//OnMainMenuClickListener.onMyListItemClick(yourObjectList.get(mSelectedPosition));
//here you inform view that something was change - view will be invalidated
notifyDataSetChanged();
}
});
return vhItem; // Returning the created object
} else if (viewType == TYPE_HEADER) {
View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.drawer_header,parent,false); //Inflating the layout
ViewHolder vhHeader = new ViewHolder(v,viewType); //Creating ViewHolder and passing the object of type view
return vhHeader; //returning the object created
}
return null;
}
//Next we override a method which is called when the item in a row is needed to be displayed, here the int position
// Tells us item at which position is being constructed to be displayed and the holder id of the holder object tell us
// which view type is being created 1 for item row
@Override
public void onBindViewHolder(MyAdapter.ViewHolder holder, int position) {
if(holder.Holderid ==1) { // as the list view is going to be called after the header view so we decrement the
// position by 1 and pass it to the holder while setting the text and image
holder.textView.setText(mNavTitles[position - 1]); // Setting the Text with the array of our Titles
holder.imageView.setImageResource(mIcons[position -1]);// Settimg the image with array of our icons
if(mSelectedPosition == position)
holder.itemView.setBackgroundColor(Color.CYAN);
else
holder.itemView.setBackgroundColor(Color.RED);
}
else{
holder.Name.setText(name);
}
}
// you can create your own listener which you set for adapter
public void setOnMainMenuClickListener(OnMyListItemClick onMyListItemClick) {
mOnMainMenuClickListener = onMyListItemClick == null ? OnMyListItemClick.NULL : onMyListItemClick;
}
// This method returns the number of items present in the list
@Override
public int getItemCount() {
return mNavTitles.length+1; // the number of items in the list will be +1 the titles including the header view.
}
// Witht the following method we check what type of view is being passed
@Override
public int getItemViewType(int position) {
if (isPositionHeader(position))
return TYPE_HEADER;
return TYPE_ITEM;
}
private boolean isPositionHeader(int position) {
return position == 0;
}
}
但是当我单击项目时，应用程序崩溃并且错误是 : Attempt to invoke virtual method 'int com.*****.******.app.MyAdapter$ViewHolder.getPosition()' on a null object reference。我做错了什么？