Question

我在viewholder patern中使用附加的类来在每次尝试使用woth适配器时实例化并重用我的项目视图

无论何时，只要我试图将视图文本设置为某个值，它就会崩溃，因为视图为空

public class SpinnerServicesAdapter extends ArrayAdapter<MyService> {
private LayoutInflater inflater;
private Context mContext;
private ArrayList<MyService> services;
private String headerTxt;

public SpinnerServicesAdapter(Context mContext, int textViewResourceId, ArrayList services, String headerTxt) {
    super(mContext, textViewResourceId, services);
    this.mContext = mContext;
    this.services = services;
    this.headerTxt = headerTxt;
    inflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}

@Override
public View getDropDownView(int position, View convertView, ViewGroup parent) {
    return getCustomView(position, convertView, parent);
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    return getCustomView(position, convertView, parent);
}
public View getCustomView(int position, View convertView, ViewGroup parent) {
    SpinnerViewHolder spinnerViewHolder;

    if (convertView == null) {
        if (position == 0) {
            convertView = inflater.inflate(R.layout.spinner_header_item_two, parent, false);
        } else {
            convertView = inflater.inflate(R.layout.spinner_item_two, parent, false);
        }
        spinnerViewHolder = new SpinnerViewHolder(convertView);
        convertView.setTag(spinnerViewHolder);
    } else {
        spinnerViewHolder = (SpinnerViewHolder) convertView.getTag();
    }

    if (position == 0) {
        spinnerViewHolder.txtVue.setText(headerTxt);
    } else {
        spinnerViewHolder.txtVue.setText(services.get(position).getName_en());
    }

    return convertView;
}

class SpinnerViewHolder {
    TextView txtVue;
    public SpinnerViewHolder(View v) {
        txtVue = (TextView) v.findViewById(R.id.spinner_item_two);
    }
}

}

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
    at com.infovas.hanger.adapters.SpinnerServicesAdapter.getCustomView(SpinnerServicesAdapter.java:60)
    at com.infovas.hanger.adapters.SpinnerServicesAdapter.getView(SpinnerServicesAdapter.java:42)
    at android.widget.AbsSpinner.onMeasure(AbsSpinner.java:197)
    at android.widget.Spinner.onMeasure(Spinner.java:507)
    at android.support.v7.widget.AppCompatSpinner.onMeasure(AppCompatSpinner.java:416)
    at android.view.View.measure(View.java:17548)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5478)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
    at android.widget.LinearLayout.measureHorizontal(LinearLayout.java:1083)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:615)
    at android.view.View.measure(View.java:17548)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5478)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
    at android.view.View.measure(View.java:17548)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5478)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
    at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:139)
    at android.view.View.measure(View.java:17548)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5478)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
    at android.view.View.measure(View.java:17548)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5478)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
    at android.view.View.measure(View.java:17548)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5478)
    at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
    at android.view.View.measure(View.java:17548)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5478)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
    at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2632)
    at android.view.View.measure(View.java:17548)
    at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2125)
    at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1238)
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1455)
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1126)
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6041)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:792)
    at android.view.Choreographer.doCallbacks(Choreographer.java:596)
    at android.view.Choreographer.doFrame(Choreographer.java:557)
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:778)
    at android.os.Handler.handleCallback(Handler.java:739)
    at android.os.Handler.dispatchMessage(Handler.java:95)

Answer 1

首先，问题是(TextView) v.findViewById(R.id.spinner_item_two)返回null（==在R.id.spinner_item_two中找不到ID为v的视图。您必须在XML布局中检查此ID是否正确。

其次，你通过位置膨胀不同的视图。问题是框架将不加区别地重用它。您必须覆盖getItemViewType(int position)才能返回两个int，每个类型的视图一个。

最后，该框架为我们提供了一个更加美观的RecyclerView方法。如果你有时间，check it。

Answer 2

您使用一个ViewHolder用于两个不同的适配器布局，这会产生可为空的视图，或者，您可以覆盖getItemViewType中的Adapter方法以确定标头项< / strong>和正常项目像这样：

1-在适配器类中定义这些常量：

private final int TYPE_HEADER = 0; private final int TYPE_ITEM = 1;

2-覆盖适配器中的getItemViewType(int position)方法：

@Override public int getItemViewType(int position) { if (isPositionHeader(position)) return TYPE_HEADER; return TYPE_ITEM; } private boolean isPositionHeader(int position) { return position == 0; }

3-为标题项创建ViewHolder课程：

class SpinnerHeaderViewHolder { TextView txtHeader; public SpinnerHeaderViewHolder(View v) { txtHeader= (TextView) v.findViewById(R.id.spinner_header_item_text_view); } }

不要忘记推荐＆＃39; txtHeader＆＃39;到（标题布局）中的正确ID

4-现在在getCustomView(int position, View convertView, @NonNull ViewGroup parent)方法中，执行以下操作：

public View getCustomView(int position, View convertView, ViewGroup parent) { final ViewHolder viewHolder; final int itemType = getItemViewType(position); if (convertView == null) { if (itemType == TYPE_HEADER) { convertView = inflater.inflate(R.layout.spinner_header_item_two, parent, false); viewHolder = new SpinnerHeaderViewHolder(convertView); } else { convertView = inflater.inflate(R.layout.spinner_item_two, parent, false); viewHolder = new SpinnerViewHolder(convertView); } convertView.setTag(viewHolder); } else { viewHolder = (ViewHolder) convertView.getTag(); } if (position == 0) { ((SpinnerHeaderViewHolder) viewHolder).txtHeader.setText(headerTxt); } else { ((SpinnerViewHolder) viewHolder).txtVue.setText(services.get(position).getName_en()); } return convertView; }

希望这会有所帮助。

Answer 3

你确定两个文件“spinner_header_item_two.xml”和“spinner_item_two.xml？

中存在id为”spinner_item_two“的textview

Android ArrayAdapter viewHolder模式giiving null视图

3 个答案: