正在获取主要活动上下文

Question

我目前正在做一个Android项目，其中有7个类：MainActivity、FragmentPagerAdapter、FragmentOne、FragmentTwo、RecyclerViewAdapter、Webview Fragment和Object类。

对象类(News(存储图像名称、标题、URL和日期。

FragmentOne和FragmentTwo是TabLayout的TabItems，它们是新闻的类别，由FragmentPagerAdapter处理。

CardView用于使用RecyclerViewAdapter填充两个片段。

但问题是，在RecyclerViewAdapter中，我无法使用在卡片视图中显示图像

getResources.getIdentifier(news.get(index).get_ImageName, drawable, mContext. getPackageName());

我猜是因为我从FragmentOne传递给RecyclerViewAdapter的上下文是片段上下文，而不是MainActivity的上下文？

以下是我的代码。

主要活动：

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ViewPager vp = findViewById(R.id.view_pager);
MyFragmentPagerAdapter adapter = new MyFragmentPagerAdapter(getSupportFragmentManager());
vp.setAdapter(adapter);
}

FragmentPagerAdapter:

private String title[]={"Cybersecurity", "AI"};
public MyFragmentPagerAdapter(@NonNull FragmentManager fm) {
super(fm);
}

@NonNull
@Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return new CybersecurityFragment();
case 1:
return new AIFragment();
}
return null;
}
@Nullable
@Override
public CharSequence getPageTitle(int position) {
return title[position];
}
@Override
public int getCount() {
return title.length;
}

customAdapter:

private Context mContext;
private List<News> newsList;
public customAdapter(Context mContext, List<News> newsList) {
this.mContext = mContext;
this.newsList = newsList;
}
@NonNull
@Override
public MyViewholder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View view;
LayoutInflater inflater = LayoutInflater.from(mContext);
view = inflater.inflate(R.layout.card_view, parent, false);
Log.d("Member", "pls1");
return new MyViewholder(view);
}
@Override
public void onBindViewHolder(@NonNull MyViewholder holder, final int position) {
holder.titleview.setText(newsList.get(position).getNews_title());
int resID = mContext.getResources().getIdentifier(newsList.get(position).getImageName(), "drawable", mContext.getPackageName());
Log.d("Member200", newsList.get(position).getImageName());
Log.d("Member100", String.valueOf(resID));
Log.d("Member", "pls");
holder.imageview.setImageResource(resID);
holder.cardview.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.d("Member", newsList.get(position).getNews_url());
WebviewFragment fragment = WebviewFragment.newInstance(newsList.get(position).getNews_url());
AppCompatActivity appCompatActivity = (AppCompatActivity) v.getContext();
appCompatActivity.getSupportFragmentManager().beginTransaction().replace(R.id.cybersecurity_rv, fragment).addToBackStack(null).commit();
}
});
}

@Override
public int getItemCount() {
return newsList.size();
}
public static class MyViewholder extends RecyclerView.ViewHolder{
CardView cardview;
TextView titleview;
ImageView imageview;
public MyViewholder(@NonNull View itemView) {
super(itemView);
cardview = itemView.findViewById(R.id.cardview);
titleview = itemView.findViewById(R.id.textView_title);
imageview = itemView.findViewById(R.id.imageView_image);
}
}

FragmentOne：

private String category, news_title, image_name, news_urls;
private Date news_date;
private ArrayList<News> newsList = new ArrayList<>();
private ArrayList<News> cybersecurity_list = new ArrayList<>();

public CybersecurityFragment() {
// Required empty public constructor
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_cybersecurity, container, false);
try{
final InputStream txtFile =getActivity().getAssets().open("news_items.txt");
BufferedReader reader = new BufferedReader(new InputStreamReader(txtFile));
String line = reader.readLine();
while (line!=null){
int colonIndex = line.indexOf(":");
if (line.contains("category")){
category = line.substring(colonIndex+1);
}
else if (line.contains("photo")) {
image_name = line.substring(colonIndex+1);
}
else if (line.contains("title"))
{
news_title = line.substring(colonIndex+1);
}
else if (line.contains("website"))
{
news_urls = line.substring(colonIndex+1);
}
else if (line.contains("date"))
{
DateFormat format = new SimpleDateFormat("dd-MM-yyyy", Locale.getDefault());
news_date = format.parse(line.substring(colonIndex+1));
}
line = reader.readLine();
if (category != null && image_name != null && news_title != null && news_urls != null && news_date != null){
newsList.add(new News(category, image_name, news_title, news_urls, news_date));
category = null;
image_name = null;
news_title = null;
news_urls = null;
news_date = null;
}
}
} catch (Exception ie){
ie.printStackTrace();
}
for (News n : newsList){
if(n.getCategory().contains("cyber")) {
cybersecurity_list.add(new News(n.getCategory(), n.getImageName(), n.getNews_title(), n.getNews_url(), n.getNews_date()));
Log.d("Member", n.getImageName());
} else {
Log.d("Member", "no");
}
}
RecyclerView rv_cs = view.findViewById(R.id.cybersecurity_rv);
customAdapter adapter = new customAdapter(getContext(), cybersecurity_list);
rv_cs.setLayoutManager(new StaggeredGridLayoutManager(2, LinearLayoutManager.VERTICAL));
rv_cs.setAdapter(adapter);
return view;
}

请告知如何解决此问题。谢谢大家！

Answer 1

编写一个Uitlity.java类

public static Drawable getDrawableFromName(Context context,String name){
Resources resources = context.getResources();
final int resourceId = resources.getIdentifier(name, "drawable", context.getPackageName());
return resources.getDrawable(resourceId);
}

holder.imageview.setImageDrawable(Utility.getDrawableFromName(mContext,code));

这对我有效