如何解决CardView 未显示在片段内
我是 Java/Android studio 的新手,只是在网上盲目学习。 我想在片段中创建一个 CardView,但是大多数示例都将 cardview 放在一个活动中,所以我搜索并更改了适当的代码。经过一段时间的修修补补,我设法让它没有错误地构建。 但是,cardview 没有显示在 RecyclerView 中。 我怀疑这是一个布局问题,但是在对 layout_height 和 layout_width 进行了所有更改之后,我无法看到 cardview。 任何帮助将不胜感激。
我的代码:
HomeFragment.java
public class HomeFragment extends Fragment implements View.OnClickListener {
final int ITEM_SIZE = 5;
public View onCreateView(@NonNull LayoutInflater inflater,@Nullable ViewGroup container,@Nullable Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment_home,container,false);
Button bh = v.findViewById(R.id.bh);
bh.setOnClickListener(this);
RecyclerView rv = (RecyclerView) v.findViewById(R.id.recyclerview);
LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
rv.setHasFixedSize(true);
rv.setLayoutManager(layoutManager);
List<Item> items = new ArrayList<>();
Item[] item = new Item[ITEM_SIZE];
item[0] = new Item(R.drawable.a,"#1");
item[1] = new Item(R.drawable.b,"#2");
item[2] = new Item(R.drawable.c,"#3");
item[3] = new Item(R.drawable.d,"#4");
item[4] = new Item(R.drawable.e,"#5");
RecyclerAdapter adaptor = new RecyclerAdapter(getActivity(),items,R.layout.fragment_home);
rv.setAdapter(adaptor);
return v;
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.bh:
((BottomNavigationView)getActivity().findViewById(R.id.nav_view)).setSelectedItemId(R.id.navigation_settings);
break;
}
}
}
RecyclerAdapter.java
public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.ViewHolder> {
Context context;
List<Item> items;
int item_layout;
public RecyclerAdapter(Context context,List<Item> items,int item_layout) {
this.context = context;
this.items = items;
this.item_layout = item_layout;
}
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent,int viewType) {
View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.fragment_home,null);
return new ViewHolder(v);
}
@Override
public void onBindViewHolder(ViewHolder holder,int position) {
final Item item = items.get(position);
Drawable drawable = ContextCompat.getDrawable(context,item.getImage());
holder.image.setBackground(drawable);
holder.title2.setText(item.getTitle());
holder.cardview.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Toast.makeText(context,item.getTitle(),Toast.LENGTH_SHORT).show();
}
});
}
@Override
public int getItemCount() {
return this.items.size();
}
public class ViewHolder extends RecyclerView.ViewHolder {
ImageView image;
TextView title2;
CardView cardview;
public ViewHolder(View itemView) {
super(itemView);
image = (ImageView) itemView.findViewById(R.id.image);
title2 = (TextView) itemView.findViewById(R.id.title2);
cardview = (CardView) itemView.findViewById(R.id.cardview);
}
}
}
Item.java
public class Item {
int image;
String title;
int getImage() { return this.image; }
String getTitle() { return this.title; }
public Item(int image,String title) {
this.image = image;
this.title = title;
}
}
fragment_home.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/MainLayout"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/text_home"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/title_home"
android:textSize="40sp"
android:textStyle="bold"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.952"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/recyclerview"
android:layout_width="0dp"
android:layout_height="wrap_content"
app:layout_constraintBottom_toTopOf="@+id/bh"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/text_home" />
<Button
android:id="@+id/bh"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="50dp"
android:text="@string/title_settings"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent" />
card.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<com.google.android.material.card.MaterialCardView
android:id="@+id/cardview"
android:layout_width="match_parent"
android:layout_height="200dp"
android:clickable="true"
android:focusable="true"
android:foreground="?android:attr/selectableItemBackground"
app:cardCornerRadius="20dp"
app:cardElevation="4dp">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
<ImageView
android:id="@+id/image"
android:layout_width="match_parent"
android:layout_height="150dp"
android:scaleType="centerCrop" />
<TextView
android:id="@+id/title2"
android:layout_width="match_parent"
android:layout_height="50dp"
android:layout_margin="5dp"
android:text="TextView"
android:textSize="25sp" />
</LinearLayout>
</com.google.android.material.card.MaterialCardView>
解决方法
似乎您在 RecyclerAdapter.java 中夸大了错误的布局
试试这个
public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.ViewHolder> {
Context context;
List<Item> items;
int item_layout;
public RecyclerAdapter(Context context,List<Item> items,int item_layout) {
this.context = context;
this.items = items;
this.item_layout = item_layout;
}
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent,int viewType) {
View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.card,null);
return new ViewHolder(v);
}
@Override
public void onBindViewHolder(ViewHolder holder,int position) {
final Item item = items.get(position);
Drawable drawable = ContextCompat.getDrawable(context,item.getImage());
holder.image.setBackground(drawable);
holder.title2.setText(item.getTitle());
holder.cardview.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Toast.makeText(context,item.getTitle(),Toast.LENGTH_SHORT).show();
}
});
}
@Override
public int getItemCount() {
return this.items.size();
}
public class ViewHolder extends RecyclerView.ViewHolder {
ImageView image;
TextView title2;
CardView cardview;
public ViewHolder(View itemView) {
super(itemView);
image = (ImageView) itemView.findViewById(R.id.image);
title2 = (TextView) itemView.findViewById(R.id.title2);
cardview = (CardView) itemView.findViewById(R.id.cardview);
}
}
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