java - 如何膨胀多张卡片 View 布局

Question

我有一个 ListView 。显示为卡片 View 。在卡片 View 中，我有一个图像，我想根据对象类型动态更改它。因此，为此我创建了两种不同的布局，其中包含小图像和大图像。我已经创建了一个适配器并尝试在 onCreateViewHolder 中膨胀两个不同的布局。我在这些代码行上遇到空指针异常。不知道我错过了什么......请帮助..

itemViewHolder.big.setImageDrawable(drawable1);
  itemViewHolder.small.setImageDrawable(drawable);
public class IAdapter extends RecyclerView.Adapter<IAdapter.ItemViewHolder> {

适配器代码

    public class ItemAdapter extends RecyclerView.Adapter<IAdapter.ItemViewHolder> {

    List<Expense> items;
    public static final int TYPE1 = 1;
    public static final int TYPE2 = 2;

    IAdapter(List<Expense> items) {

        this.items = items;

    }

    @Override
    public int getItemCount() {
        return items.size();

    }

    @Override
    public int getItemViewType(int position) {

        Expense e = new Expense();
        if (TYPE1 == 1) {
            int type = e.getExpenseType();
            return type;
        } else {
            return TYPE2;
        }

    }

    @Override
    public void onBindViewHolder(ItemViewHolder itemViewHolder, int i) {

        itemViewHolder.amount.setText(items.get(i).amount);
        itemViewHolder.expense.setText(items.get(i).expense);
        TextDrawable drawable = TextDrawable.builder()
                .beginConfig()
                .withBorder(4)
                .textColor(Color.BLACK)
                .useFont(Typeface.DEFAULT)
                .fontSize(25)
                .bold()
                .toUpperCase()
                .endConfig()
                .buildRound("11:00", Color.GRAY);
        itemViewHolder.small.setImageDrawable(drawable);

        TextDrawable drawable1 = TextDrawable.builder()
                .beginConfig()
                .withBorder(4)
                .textColor(Color.BLACK)
                .useFont(Typeface.DEFAULT)
                .fontSize(25)
                .bold()
                .toUpperCase()
                .endConfig()
                .buildRound("10 Jan", Color.CYAN);
        itemViewHolder.big.setImageDrawable(drawable1);

    }

    @Override
    public ItemViewHolder onCreateViewHolder(ViewGroup viewGroup, int viewType) {

        if (viewType == TYPE1) {
            View itemView = LayoutInflater.
                    from(viewGroup.getContext()).
                    inflate(R.layout.cardlayout, viewGroup, false);
            return new ItemViewHolder(itemView, viewType);
        } else {
            View itemView = LayoutInflater.
                    from(viewGroup.getContext()).
                    inflate(R.layout.bigcircle, viewGroup, false);
            ItemViewHolder ivh = new ItemViewHolder(itemView, viewType);
            return ivh;
        }
    }

    public static class ItemViewHolder extends RecyclerView.ViewHolder {
        CardView cv;
        TextView amount;
        TextView expense;
        ImageView small;
        ImageView big;

        ItemViewHolder(View itemView, int viewType) {
            super(itemView);
            amount = (TextView) itemView.findViewById(R.id.txtAmount);
            expense = (TextView) itemView.findViewById(R.id.txtexpense);
            cv = (CardView) itemView.findViewById(R.id.card_view);
            small = (ImageView) itemView.findViewById(R.id.small);
            big=(ImageView)itemView.findViewById(R.id.big);
            //   cv1 = (CardView) itemView.findViewById(R.id.card_view);

            //TextDrawable drawable1 = TextDrawable.builder()
            // .buildRound("20 Jan", Color.RED);

        }
    }


    @Override
    public void onAttachedToRecyclerView(RecyclerView recyclerView) {
        super.onAttachedToRecyclerView(recyclerView);
    }

}

卡片布局代码

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:card_view="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:weightSum="1"
android:orientation="vertical"
android:measureWithLargestChild="false"
android:background="@android:color/white">
<!-- A CardView that contains a TextView -->

<android.support.v7.widget.CardView
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    android:id="@+id/card_view"
    android:layout_width="match_parent"
    android:layout_height="80dp"
    card_view:cardCornerRadius="4dp"
    android:background="@android:color/white">


    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/relativeLayout"
        android:background="@android:color/white"
        android:layout_alignParentTop="true">


        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textAppearance="?android:attr/textAppearanceMedium"
            android:id="@+id/txtAmount"
            android:text="text1"
            android:layout_centerVertical="true"
            android:layout_toLeftOf="@+id/linearLayout"
            android:layout_toStartOf="@+id/linearLayout"
            android:layout_marginRight="24dp"
            android:layout_marginEnd="24dp" />

        <LinearLayout
            android:orientation="vertical"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:weightSum="1"
            android:id="@+id/linearLayout"
            android:gravity="center_vertical"
            android:layout_alignParentTop="true"
            android:layout_centerHorizontal="true">


            <ImageView
                android:layout_width="40dp"
                android:layout_height="25dp"
                android:id="@+id/imageView2"
                android:background="@drawable/line" />

            <ImageView

                android:id="@+id/small"
                android:focusableInTouchMode="false"
                android:layout_width="40dp"
                android:layout_height="40dp"
                android:background="@drawable/circle"/>


            <ImageView
                android:layout_width="40dp"
                android:layout_height="25dp"
                android:id="@+id/imageView3"
                android:background="@drawable/line" />
        </LinearLayout>

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textAppearance="?android:attr/textAppearanceMedium"
            android:text="Medium Text"
            android:id="@+id/txtexpense"
            android:layout_centerVertical="true"
            android:layout_toRightOf="@+id/linearLayout"
            android:layout_toEndOf="@+id/linearLayout"
            android:layout_marginLeft="24dp"
            android:layout_marginStart="24dp" />
    </RelativeLayout>

</android.support.v7.widget.CardView>

大圆卡布局代码

  <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:weightSum="1"
    android:orientation="vertical"
    android:measureWithLargestChild="false">
    <!-- A CardView that contains a TextView -->

    <android.support.v7.widget.CardView
        xmlns:card_view="http://schemas.android.com/apk/res-auto"
        android:id="@+id/card_view1"
        android:layout_width="match_parent"
        android:layout_height="80dp"
        card_view:cardCornerRadius="4dp"
        android:background="@android:color/white">


        <RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:id="@+id/relativeLayout"
            android:background="@android:color/white"
            android:layout_alignParentTop="true">


            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:textAppearance="?android:attr/textAppearanceMedium"
                android:id="@+id/txtAmount"
                android:text="text1"
                android:layout_centerVertical="true"
                android:layout_toLeftOf="@+id/linearLayout"
                android:layout_toStartOf="@+id/linearLayout"
                android:layout_marginRight="24dp"
                android:layout_marginEnd="24dp" />

            <LinearLayout
                android:orientation="vertical"
                android:layout_width="wrap_content"
                android:layout_height="match_parent"
                android:weightSum="1"
                android:id="@+id/linearLayout"
                android:gravity="center_vertical"
                android:layout_alignParentTop="true"
                android:layout_centerHorizontal="true">


                <ImageView
                    android:layout_width="50dp"
                    android:layout_height="25dp"
                    android:id="@+id/imageView2"
                    android:background="@drawable/line" />

                <ImageView

                    android:id="@+id/big"
                    android:focusableInTouchMode="false"
                    android:layout_width="50dp"
                    android:layout_height="50dp"
                    android:background="@drawable/circle1"/>


                <ImageView
                    android:layout_width="50dp"
                    android:layout_height="25dp"
                    android:id="@+id/imageView3"
                    android:background="@drawable/line" />
            </LinearLayout>

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:textAppearance="?android:attr/textAppearanceMedium"
                android:text="Medium Text"
                android:id="@+id/txtexpense"
                android:layout_centerVertical="true"
                android:layout_toRightOf="@+id/linearLayout"
                android:layout_toEndOf="@+id/linearLayout"
                android:layout_marginLeft="24dp"
                android:layout_marginStart="24dp" />
        </RelativeLayout>

    </android.support.v7.widget.CardView>
</LinearLayout>

我错过了什么？？？

Answer 1

这是因为您在 onBindViewHolder 方法中使用了从 onCreateViewHolder 方法传递过来的 ItemViewHolder。它失败的原因是，您传递了 2 个不同的膨胀 View ，一个包含 id big 的 View 元素，另一个包含 id small 的 View 元素。因此，itemViewHolder.big 或 itemViewHolder.small 变为空。抛出一个 NullPointerException

我认为您处理此问题的方式是正确的。

选项一:这是一种不同的实现方式。

如果你对这两个有完全不同的布局，你必须这样做。但是，如果卡片的布局相同，只是那些大图像和小图像发生了变化，我建议您保持单一布局并在语法上更改 ImageView 。

方案二

你的方法。我建议你坚持下去，因为这是做到这一点的优雅方式。但是你将不得不做一些小的调整。

    @Override
    public int getItemViewType(int position) {
          return items.get(position).getExpenseType();// Assume that this return 1 0r 2
    }

我建议您在此处设置值之前检查类型，假设您有一个 TYPE 类变量来保留每个项目的类型。

@Override
    public void onBindViewHolder(ItemViewHolder itemViewHolder, int i) {

       itemViewHolder.amount.setText(items.get(i).amount);
       itemViewHolder.expense.setText(items.get(i).expense);

       if(getItemViewType(i) == 1){
        TextDrawable drawable = TextDrawable.builder()
                .beginConfig()
                .withBorder(4)
                .textColor(Color.BLACK)
                .useFont(Typeface.DEFAULT)
                .fontSize(25)
                .bold()
                .toUpperCase()
                .endConfig()
                .buildRound("11:00", Color.GRAY);
        itemViewHolder.small.setImageDrawable(drawable);
       }else{
        TextDrawable drawable1 = TextDrawable.builder()
                .beginConfig()
                .withBorder(4)
                .textColor(Color.BLACK)
                .useFont(Typeface.DEFAULT)
                .fontSize(25)
                .bold()
                .toUpperCase()
                .endConfig()
                .buildRound("10 Jan", Color.CYAN);
        itemViewHolder.big.setImageDrawable(drawable1);
      }
    }

这并没有改变我的答案。但这会给你一个好主意。你缺的空腔东西就在这，

public static class ItemViewHolder extends RecyclerView.ViewHolder {
        CardView cv;
        TextView amount;
        TextView expense;
        ImageView small;
        ImageView big;

        ItemViewHolder(View itemView, int viewType) {
            super(itemView);
            amount = (TextView) itemView.findViewById(R.id.txtAmount);
            expense = (TextView) itemView.findViewById(R.id.txtexpense);
            cv = (CardView) itemView.findViewById(R.id.card_view);
            small = (ImageView) itemView.findViewById(R.id.small);
            big=(ImageView)itemView.findViewById(R.id.big);
            //   cv1 = (CardView) itemView.findViewById(R.id.card_view);

            //TextDrawable drawable1 = TextDrawable.builder()
            // .buildRound("20 Jan", Color.RED);

        }
    }

即使你这样做

small = (ImageView) itemView.findViewById(R.id.small);
big=(ImageView)itemView.findViewById(R.id.big);

small 或 big 变量将被分配 null。但是你必须在调用它的方法之前检查它。否则它会给出一个 NullPointerException

编辑:

或者你可以这样做，

@Override
public ItemViewHolder onCreateViewHolder(ViewGroup viewGroup,int viewType) {

    View itemView;
    if (getItemViewType(i)==1) {
        itemView = LayoutInflater.
                from(viewGroup.getContext()).
                inflate(R.layout.cardlayout, viewGroup, false);

    } else {
        itemView = LayoutInflater.from(viewGroup.getContext()).
                inflate(R.layout.bigcircle, viewGroup, false);
    }

    return new ItemViewHolder(itemView,viewType);
}