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[英]How to implement a listview with an adapter in a fragment in Android Studio
[英]How to implement custom adapter to a nested fragment
我试图在嵌套片段中创建一个列表视图,该片段将作为元素图像并在其下带有标题,尽管我在为填充列表视图而创建的自定义适配器中不断出现nullpointer错误。 这是代码:
定制适配器:
import android.app.Activity;
import android.view.View;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;
import java.util.ArrayList;
import java.util.List;
public class ImageAdapter extends ArrayAdapter<Image> {
ArrayList<Image> imageList;
private Context mContext;
int resource;
public ImageAdapter(Context context, int resource, ArrayList<Image> imageObjects) {
super(context, resource, imageObjects);
this.imageList = imageObjects;
this.mContext = context;
this.resource = resource;
}
public ArrayList<Image> getImageList() {
return imageList;
}
public void setImageList(ArrayList<Image> imageList) {
this.imageList = imageList;
}
public Context getmContext() {
return mContext;
}
public void setmContext(Context mContext) {
this.mContext = mContext;
}
public int getResource() {
return resource;
}
public void setResource(int resource) {
this.resource = resource;
}
@Override
public View getView(int position, View convertView, ViewGroup parent){
if(convertView==null){
LayoutInflater layoutInflater = (LayoutInflater) getContext().getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
convertView = layoutInflater.inflate(R.layout.fragment_membership, null, true);
}
Image image = getItem(position);
ImageView layoutImage = (ImageView)convertView.findViewById(R.id.membershipimage);
layoutImage.setImageResource(image.getImageResourceID());
TextView layoutText = (TextView)convertView.findViewById(R.id.membershipCaption);
layoutText.setText(image.getImageCaption());
return super.getView(position, convertView, parent);
}
}
我在另一个片段中使用的片段:
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.GridView;
import android.widget.ListView;
import java.util.ArrayList;
public class MembershipFragment extends Fragment {
ArrayList<Image> imageList;
ListView membershipListView;
public static MembershipFragment newInstance() {
MembershipFragment fragment = new MembershipFragment();
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_membership, container, false);
return view;
}
@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
imageList = new ArrayList<>();
for(int i=0; i<3; i++){
Image image = new Image(R.drawable.cinnamon_apple_breakfast, "Test Caption");
imageList.add(image);
}
membershipListView = (ListView)view.findViewById(R.id.membershipListView);
try{
ImageAdapter adapter = new ImageAdapter(getContext(), R.layout.list_view_item, imageList);
membershipListView.setAdapter(adapter);
}
catch (Exception e){
e.printStackTrace();
}
}
}
当我尝试将图像资源ID设置为imageview时,该应用程序始终在启动时崩溃,并在getView方法的自定义适配器中引发nullpointer异常。 问题出在哪儿?
我认为您在混淆自己的布局。
您应该在这里使用getActivity
。
ImageAdapter adapter = new ImageAdapter(getContext(), R.layout.list_view_item
您在那里传递了布局资源。 但是在适配器内部,您使用的是不同的布局。
@Override
public View getView(int position, View convertView, ViewGroup parent){
if(convertView==null){
LayoutInflater layoutInflater = (LayoutInflater) getContext().getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
convertView = layoutInflater.inflate(R.layout.fragment_membership, null, true);
}
我假设您做了一个getResource
方法,这是有原因的吗? 你永远都不会打电话。
我认为您不希望Fragment布局保存Fragment布局列表(因为递归)
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_membership, container, false);
return view;
}
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