java - 使用 Picasso Library 目标不能为空

Question

我使用 Picasso Library 2.4.0 实现了一个 listView，但我遇到了一个问题。发生了什么:我使用 Android Studio 启动应用程序，然后转到我实现了 listView 的特定 fragment ，一切看起来都正常(所有图像都在加载，对于 TextView) 但如果我尝试向下滚动应用程序崩溃。这是它告诉我的:

2-03 19:45:38.290  31501-31501/com.zenyt E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.IllegalArgumentException: Target must not be null.
            at com.squareup.picasso.RequestCreator.into(RequestCreator.java:553)
            at com.squareup.picasso.RequestCreator.into(RequestCreator.java:536)
            at com.zenyt.Volvo.Volvo1$SampleListViewAdapter.getView(Volvo1.java:106)
            at android.widget.AbsListView.obtainView(AbsListView.java:2445)
            at android.widget.ListView.makeAndAddView(ListView.java:1775)
            at android.widget.ListView.fillDown(ListView.java:678)
            at android.widget.ListView.fillGap(ListView.java:642)
            at android.widget.AbsListView.trackMotionScroll(AbsListView.java:5525)
            at android.widget.AbsListView.scrollIfNeeded(AbsListView.java:3413)
            at android.widget.AbsListView.onTouchEvent(AbsListView.java:3901)
            at android.view.View.dispatchTouchEvent(View.java:7337)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2410)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2145)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2416)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2159)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2416)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2159)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2416)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2159)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2416)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2159)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2416)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2159)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2416)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2159)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2416)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2159)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2416)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2159)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2416)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2159)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2416)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2159)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2416)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2159)
            at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2115)
            at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1468)
            at android.app.Activity.dispatchTouchEvent(Activity.java:2487)
            at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2063)
            at android.view.View.dispatchPointerEvent(View.java:7520)
            at android.view.ViewRootImpl.deliverPointerEvent(ViewRootImpl.java:3376)
            at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:3308)
            at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:4402)
            at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:4380)
            at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:4484)
            at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:171)
            at android.view.InputEventReceiver.nativeConsumeBatchedInputEvents(Native Method)
            at android.view.InputEventReceiver.consumeBatchedInputEvents(InputEventReceiver.java:163)
            at android.view.ViewRootImpl.doConsumeBatchedInput(ViewRootImpl.java:4452)
            at android.view.ViewRootImpl$ConsumeBatchedInputRunnable.run(ViewRootImpl.java:4503)
            at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725)
            at android.view.Choreographer.doCallbacks(Choreographer.java:555)
            at android.view.Choreographer.doFrame(Choreographer.java:523)
            at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711

它指向这一行:at com.zenyt.Volvo.Volvo1$SampleListViewAdapter.getView(Volvo1.java:106) 这是:Picasso.with(context)

 public final class SampleListViewAdapter extends BaseAdapter {
        private final Context context;
        private final List<String> urls = new ArrayList<>();
        private final List<String> models = new ArrayList<>();
        private final List<String> price = new ArrayList<>();
        public SampleListViewAdapter (Context context) {
            this.context = context;
            Collections.addAll(urls, Data.Volvo1URLS);
            Collections.addAll(models, Data.VolvoModels);
            Collections.addAll(price, Data.VolvoPrice);
        }

        @Override public View getView(int position, View view, ViewGroup parent) {
            ViewHolder holder;
            ViewHolder holder1;
            if (view == null) {
                view = LayoutInflater.from(context).inflate(R.layout.sample_list_detail_item, parent, false);

                holder = new ViewHolder();
                holder1 = new ViewHolder();

                holder.image = (ImageView) view.findViewById(R.id.photo);
                holder.text = (TextView) view.findViewById(R.id.url);
                holder1.text = (TextView) view.findViewById(R.id.price);

                view.setTag(holder);
                view.setTag(holder1);
            } else {
                holder = (ViewHolder) view.getTag();
                holder1 = (ViewHolder) view.getTag();
            }
            // Get the image URL for the current position.
            String url = getItem(position);
            String models = getItem1(position);
            String price = getItem2(position);

            holder.text.setText(models);
            holder.text.setTextSize(16);

            holder1.text.setText(price);
            holder1.text.setTextSize(16);

            // Trigger the download of the URL asynchronously into the image view.
            Picasso.with(context)
                    .load(url)
                    .placeholder(R.drawable.placeholder)
                    .error(R.drawable.error)
                    .resizeDimen(R.dimen.list_detail_image_size, R.dimen.list_detail_image_size)
                    .centerInside()
                    .tag(context)
                    .into(holder.image);

            return view;
        }

        @Override public int getCount() {
            return urls.size();
        }

        @Override public String getItem(int position) {
            return urls.get(position);
        }
        private String getItem1(int position) {
            return models.get(position);
        }
        private String getItem2(int position) {
            return price.get(position);
        }

        @Override public long getItemId(int position) {
            return position;
        }

         class ViewHolder {
            ImageView image;
            TextView text;
        }
    }

在我添加第二个 holder -> holder1 之前，该应用程序运行良好。如果我删除属于此 holder1 的所有行，应用程序可以正常工作。

sample_list_detail_item.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal"
    android:padding="8dp"
    android:background="@android:color/black">

    <ImageView
        android:id="@+id/photo"
        android:layout_width="@dimen/list_detail_image_size"
        android:layout_height="@dimen/list_detail_image_size"
        />
    <TextView
        android:id="@+id/url"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:layout_marginLeft="5dp"
        android:layout_marginStart="5dp"
        android:layout_gravity="start|center_vertical"
        />

    <TextView
        android:id="@+id/price"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:layout_gravity="start|center"
        />
</LinearLayout>

对不起我的英语。

Answer 1

错误的发生是因为 holder.image 为 null - 而 into() 专门检查您传入的参数是否为 null。

当您使用setTag()/getTag()时，只能存储一个对象。因此当你打电话时

view.setTag(holder);
view.setTag(holder1);

holder 中的数据均未保存 - 它被替换为 holder1。与其拥有多个 ViewHolder，不如将另一个字段添加到现有的 ViewHolder 类:

class ViewHolder {
  ImageView image;
  TextView url;
  TextView price;
}

然后你可以只使用一个ViewHolder:

holder = new ViewHolder();

holder.image = (ImageView) view.findViewById(R.id.photo);
holder.url = (TextView) view.findViewById(R.id.url);
holder.price = (TextView) view.findViewById(R.id.price);

view.setTag(holder);