Question

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>

Answer 1

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);
    }
}

CardView 未显示在片段内

1 个答案: