Java 设置自定义ListView图像时出错
我想用Java 设置自定义ListView图像时出错,java,android,listview,android-listview,android-arrayadapter,Java,Android,Listview,Android Listview,Android Arrayadapter,我想用ArrayAdapter设置自定义ListView。每个列表项都有一个图像视图和两个文本视图 每个项目的布局rowlayout.xml: <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" > <ImageView and
ArrayAdapter
设置自定义ListView
。每个列表项
都有一个图像视图
和两个文本视图
每个项目的布局rowlayout.xml
:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<ImageView
android:id="@+id/item_icon"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:adjustViewBounds="true"
android:maxHeight="80dp"
android:maxWidth="80dp"
android:src="@drawable/logo" />
<TextView
android:id="@+id/item_title"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_above="@+id/item_subTitle"
android:layout_toRightOf="@+id/item_icon"
android:text="Titel"
android:textAppearance="?android:attr/textAppearanceLarge" />
<TextView
android:id="@+id/item_subTitle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBottom="@+id/item_icon"
android:layout_alignLeft="@+id/item_title"
android:layout_marginBottom="16dp"
android:text="Untertitel" />
</RelativeLayout>
以下是徽章类别:
public class Badge {
String title;
String subtitle;
int iconID;
public Badge(String title, String subtitle, int iconID) {
this.title = title;
this.subtitle = subtitle;
this.iconID = iconID;
}
public String getTitle() {
return title;
}
public String getSubtitle() {
return subtitle;
}
public int getIconID() {
return iconID;
}
}
我得到以下错误:
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageResource(int)' on a null object reference
我在代码中标记了发生错误的行。这可能是什么原因?而不是使用
ImageView itemIcon = (ImageView) findViewById(R.id.item_icon);
TextView itemTitle = (TextView) findViewById(R.id.item_title);
TextView itemSubtitle = (TextView) findViewById(R.id.item_subTitle);
使用
替换
ImageView itemIcon = (ImageView) findViewById(R.id.item_icon);
这个
ImageView itemIcon = (ImageView) itemView.findViewById(R.id.item_icon);
同样地
TextView itemTitle = (TextView) itemView.findViewById(R.id.item_title);
TextView itemSubtitle = (TextView) itemView.findViewById(R.id.item_subTitle);
与
您刚才膨胀的视图没有添加到活动的布局中。活动方法也是如此
ImageView itemIcon = (ImageView) findViewById(R.id.item_icon);
itemIcon.setImageResource(currentBadge.getIconID());
找不到具有特定id的视图。相反,应使用
ImageView itemIcon = (ImageView) itemView.findViewById(R.id.item_icon);
itemIcon.setImageResource(currentBadge.getIconID());
它会正常工作。其他视图类似。我认为您的问题在这一行:ArrayAdapter=new MyListAdapter() 更改为:MyListAdapter=new MyListAdapter() 另外,将项目视图放在findViewById方法前面(ImageView itemIcon=(ImageView)itemview.findViewById(R.id.item_icon);) 实际上,我建议泛化您的适配器类,这样您就可以将任何资源(行布局)和列表传递给它:)(但是,应用程序不必工作) 比如说:
private class MyListAdapter extends ArrayAdapter<Badge> {
int resource;
public MyListAdapter(Context context, int resource, List<Badge> items) {
super(context, resource, items);
this.resource = resource;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View itemView = convertView;
if(itemView == null) {
itemView = getLayoutInflater().inflate(resource, parent, false);
}
Badge currentBadge = getItem(position);
ImageView itemIcon = (ImageView) itemview.findViewById(R.id.item_icon);
//the error is on the following line:
itemIcon.setImageResource(currentBadge.getIconID());
TextView itemTitle = (TextView) itemview.findViewById(R.id.item_title);
itemTitle.setText(currentBadge.getTitle());
TextView itemSubtitle = (TextView) itemview.findViewById(R.id.item_subTitle);
itemSubtitle.setText(currentBadge.getSubtitle());
return itemView;
}
}
私有类MyListAdapter扩展了ArrayAdapter{
智力资源;
公共MyListAdapter(上下文、int资源、列表项){
超级(上下文、资源、项目);
这个资源=资源;
}
@凌驾
公共视图getView(int位置、视图转换视图、视图组父视图){
视图项视图=转换视图;
如果(itemView==null){
itemView=GetLayoutFlater().inflate(资源、父项、false);
}
Badge currentBadge=getItem(位置);
ImageView itemIcon=(ImageView)itemview.findViewById(R.id.item_图标);
//错误出现在以下行:
setImageResource(currentBadge.getIconID());
TextView itemTitle=(TextView)itemview.findViewById(R.id.item\u title);
itemTitle.setText(currentBadge.getTitle());
TextView itemstitle=(TextView)itemview.findViewById(R.id.item\u subTitle);
itemstitle.setText(currentBadge.getSubtitle());
返回项目视图;
}
}
ImageView itemIcon = (ImageView) findViewById(R.id.item_icon);
itemIcon.setImageResource(currentBadge.getIconID());
ImageView itemIcon = (ImageView) itemView.findViewById(R.id.item_icon);
itemIcon.setImageResource(currentBadge.getIconID());
private class MyListAdapter extends ArrayAdapter<Badge> {
int resource;
public MyListAdapter(Context context, int resource, List<Badge> items) {
super(context, resource, items);
this.resource = resource;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View itemView = convertView;
if(itemView == null) {
itemView = getLayoutInflater().inflate(resource, parent, false);
}
Badge currentBadge = getItem(position);
ImageView itemIcon = (ImageView) itemview.findViewById(R.id.item_icon);
//the error is on the following line:
itemIcon.setImageResource(currentBadge.getIconID());
TextView itemTitle = (TextView) itemview.findViewById(R.id.item_title);
itemTitle.setText(currentBadge.getTitle());
TextView itemSubtitle = (TextView) itemview.findViewById(R.id.item_subTitle);
itemSubtitle.setText(currentBadge.getSubtitle());
return itemView;
}
}