我想要一个RecyclerView for Multple＆amp;不同的布局，我无法解决此错误。
错误：java.lang.NullPointerException：尝试在空对象引用上调用虚方法'void android.widget.ImageView.setImageResource（int）'
错误代码
（（ViewHolder1）holder）.mIdView.setImageResource（（（ViewHolder1）holder）.mItem.id）
DataAdapter的
package krishidarshan;
import android.content.Context;
import android.content.Intent;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import java.util.List;
import krishidarshan.dummy.DummyContent.DummyItem;
/**
* Created by Abhishek on 19-03-2017.
*/
public class DataAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
private final List<DummyItem> mValues;
int type;
public DataAdapter(List<DummyItem> items, int layoutType) {
mValues = items;
type = layoutType;
}
@Override
public int getItemViewType(int position) {
return type;
}
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
if (viewType == 1) {
View view1 = LayoutInflater.from(parent.getContext())
.inflate(R.layout.card_view, parent, false);
return new ViewHolder1(view1);
} else {
View view2 = LayoutInflater.from(parent.getContext())
.inflate(R.layout.fragment_crops, parent, false);
return new ViewHolder2(view2);
}
}
@Override
public void onBindViewHolder(final RecyclerView.ViewHolder holder, final int position) {
if (holder instanceof ViewHolder1) {
((ViewHolder1) holder).mItem = mValues.get(position);
((ViewHolder1) holder).mIdView.setImageResource(((ViewHolder1) holder).mItem.id);
((ViewHolder1) holder).mIdView.setImageResource(((ViewHolder1) holder).mItem.id);
((ViewHolder1) holder).mContentView.setText(((ViewHolder1) holder).mItem.content);
} else if (holder instanceof ViewHolder2) {
((ViewHolder2) holder).mItem = mValues.get(position);
((ViewHolder2) holder).mIdView.setImageResource(((ViewHolder2) holder).mItem.id);
((ViewHolder2) holder).mContentView.setText(((ViewHolder2) holder).mItem.content);
((ViewHolder2) holder).mContentDetailView.setText(((ViewHolder2) holder).mItem.content_detail);
}
}
@Override
public int getItemCount() {
return mValues.size();
}
public class ViewHolder1 extends RecyclerView.ViewHolder {
public final View mView;
public final ImageView mIdView;
public final TextView mContentView;
public final Context mContext;
public DummyItem mItem;
public ViewHolder1(final View view) {
super(view);
mView = view;
mContext = view.getContext();
mIdView = (ImageView) view.findViewById(R.id.id);
mContentView = (TextView) view.findViewById(R.id.content);
view.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
int position = getAdapterPosition();
switch (position) {
case 0:
Intent i = new Intent(mContext, CropsActivity.class);
mContext.startActivity(i);
break;
case 1:
Intent i1 = new Intent(mContext, WeatherActivity.class);
mContext.startActivity(i1);
}
}
});
}
@Override
public String toString() {
return super.toString() + " '" + mContentView.getText() + "'";
}
}
public class ViewHolder2 extends RecyclerView.ViewHolder {
public final View mView;
public final ImageView mIdView;
public final TextView mContentView, mContentDetailView;
public final Context mContext;
public DummyItem mItem;
public ViewHolder2(final View view) {
super(view);
mView = view;
mContext = view.getContext();
mIdView = (ImageView) view.findViewById(R.id.crops_image);
mContentView = (TextView) view.findViewById(R.id.crops_name);
mContentDetailView = (TextView) view.findViewById(R.id.crops_detail);
}
@Override
public String toString() {
return super.toString() + " '" + mContentView.getText() + "'";
}
}
}
DummyContent
package krishidarshan.dummy;
/**
* Created by Abhishek on 19-03-2017.
*/
import java.util.ArrayList;
import java.util.List;
import krishidarshan.R;
/**
* Helper class for providing sample content for user interfaces created by
* Android template wizards.
* <p/>
* TODO: Replace all uses of this class before publishing your app.
*/
public class DummyContent {
/**
* An array of sample (dummy) items.
*/
public static final List<DummyItem> ITEMS = new ArrayList<>();
public static final List<DummyItem> CROPS_ITEMS = new ArrayList<>();
private static String[] item_names = {"Crops", "Weather", "Market Price", "ABC"};
private static int[] item_list = {R.drawable.bg, R.drawable.bg, R.drawable.bg, R.drawable.bg};
private static String[] crops_names = {"Rice", "Wheat", "Jwar", "Bajra"};
private static int[] crops_images = {R.drawable.bg, R.drawable.bg, R.drawable.bg, R.drawable.bg};
private static String[] crops_content = {"They are useful", "They are useful", "They are useful", "They are useful"};
private static final int COUNT = 4;
static {
// Add some sample items.
for (int i = 0; i < COUNT; i++) {
addItem(createDummyItem(i));
addItemForCrop(createCropItem(i));
}
}
private static void addItem(DummyItem item) {
ITEMS.add(item);
}
private static void addItemForCrop(DummyItem item) {
CROPS_ITEMS.add(item);
}
private static DummyItem createDummyItem(int position) {
return new DummyItem(item_list[position], item_names[position]);
}
private static DummyItem createCropItem(int position) {
return new DummyItem(crops_images[position], crops_names[position], crops_content[position]);
}
/**
* A dummy item representing a piece of content.
*/
public static class DummyItem {
public final int id;
public final String content;
public final String content_detail;
public DummyItem(int id, String content) {
this.id = id;
this.content = content;
this.content_detail = null;
}
@Override
public String toString() {
return content;
}
public DummyItem(int id, String content, String content_detail) {
this.id = id;
this.content = content;
this.content_detail = content_detail;
}
}
}
card_view.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:card_view="http://schemas.android.com/apk/res-auto"
android:id="@+id/card"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="4dp"
android:elevation="4dp"
android:foreground="?selectableItemBackground"
card_view:cardBackgroundColor="#ffffff"
card_view:cardCornerRadius="6dp"
card_view:contentPadding="0.2dp">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
<ImageView
android:id="@+id/id"
android:layout_width="match_parent"
android:layout_height="150dp"
android:adjustViewBounds="true"
android:scaleType="fitXY" />
<TextView
android:id="@+id/content"
android:layout_width="match_parent"
android:layout_height="40dp"
android:layout_alignBottom="@+id/id"
android:alpha="0.8"
android:background="#757575"
android:gravity="center"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:text="Crops"
android:textSize="17dp" />
</RelativeLayout>
答案 0 :(得分：0)
试试这个，它应该有效：
if (holder instanceof ViewHolder1) {
((ViewHolder1) holder).bind(mValues.get(position));
} else {
// more code here! ...
}