我是新来的，所以请忍受我的天真。我正在制作一个音乐播放器，它会在listview项目中点击'dots'按钮（在下面的代码中给出）显示一个菜单。菜单内部会有一个要删除的按钮。列表视图将由自定义适配器填充。这是适配器的代码......
private class hashmapAdapter extends BaseAdapter implements Filterable {
HashMap<Integer, NowPlayingActivity.Details> NewDetails = new HashMap<>();
private hashmapAdapter(HashMap<Integer, NowPlayingActivity.Details> hashMap) {
if(NewDetails.size()==0) {
NewDetails.putAll(hashMap);
}
}
@Override
public int getCount() {
return NewDetails.size();
}
@Override
public Object getItem(int position) {
return NewDetails.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(final int position, View convertView, ViewGroup parent) {
final View result;
if(convertView == null) {
result = LayoutInflater.from(parent.getContext()).inflate(R.layout.single_item,parent,false);
} else {
result = convertView;
}
((TextView)result.findViewById(R.id.Name)).setText(NewDetails.get(position).getName());
((TextView)result.findViewById(R.id.artist)).setText(NewDetails.get(position).getArtist());
((TextView)result.findViewById(R.id.duration)).setText(NewDetails.get(position).getDuration()+" || ");
dots = (Button)result.findViewById(R.id.dots);
dots.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
name = (TextView)result.findViewById(R.id.Name);
LayoutInflater inflater = (LayoutInflater)getSystemService(LAYOUT_INFLATER_SERVICE);
View popup_view = inflater.inflate(R.layout.option_layout,null);
RelativeLayout item = (RelativeLayout) popup_view.findViewById(R.id.popup);
final float width= (getResources().getDimension(R.dimen.width_entry_in_dp));
final float height= getResources().getDimension(R.dimen.height_entry_in_dp);
final PopupWindow popupWindow = new PopupWindow(popup_view,Math.round(width),Math.round(height),true);
popupWindow.showAtLocation(item, Gravity.END, 0, 0);
popupWindow.showAsDropDown(dots);
play_next_btn = (Button)popup_view.findViewById(R.id.play_next);
add_to_playlist = (Button)popup_view.findViewById(R.id.add_to_playlist);
share = (Button)popup_view.findViewById(R.id.share);
delete = (Button)popup_view.findViewById(R.id.delete);
delete.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
for(int i=0;i<NewDetails.size();i++) {
if(NewDetails.get(i).getName().equals(name.getText().toString())) {
for(int j=0;j<hashMap.size();j++) {
if(hashMap.get(j).getName().equals(name.getText().toString())) {
if (true) {
NewDetails.remove(i);
hashMap.remove(j);
}
}
}
}
}
populate1(NewDetails);
popupWindow.dismiss();
}
});
}
});
return result;}
现在的问题是，当我调用populate1（NewDetails）时删除元素后，它会在NewDetails.get（position）.getName（）上给出一个空指针异常。所以在重新填充listview时我得到了NPE错误。以下是populate1（）函数代码......
public void populate1(HashMap<Integer,NowPlayingActivity.Details> hashMap) {
adapter = new hashmapAdapter(hashMap);
library.setAdapter(adapter);
adapter.notifyDataSetChanged();
library.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
name = (TextView)view.findViewById(R.id.Name);
String SongName = name.getText().toString();
Intent intent = new Intent(getApplicationContext(),NowPlayingActivity.class);
intent.putExtra("SongName",SongName);
setResult(555,intent);
finish();
}
});
}
我已经尝试过notifydatasetchanged（）和listview.invalidateviews（），两者都没有用。文件被删除但适配器没有刷新列表以删除元素。这是listview的single_item的xml布局....`
`<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="horizontal" android:layout_width="wrap_content"
android:layout_height="70dp"
android:paddingRight="8dp"
android:paddingEnd="8dp"
android:background="@drawable/element_shape_list"
android:descendantFocusability="blocksDescendants">
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/v1"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_centerVertical="true"
android:foreground="?android:attr/selectableItemBackground">
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/v11"
android:orientation="horizontal" android:layout_width="wrap_content"
android:layout_height="match_parent">
<ImageView
android:id="@+id/art_work"
android:layout_width="60dp"
android:layout_height="60dp"
android:layout_centerVertical="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:background="@mipmap/ic_launcher"
android:layout_marginLeft="5dp"
android:layout_marginStart="5dp"/>
<TextView
android:id="@+id/Name"
android:textSize="17sp"
android:textColor="#000"
android:textStyle="bold"
android:gravity="bottom"
android:layout_width="match_parent"
android:layout_height="30dp"
android:layout_marginTop="10dp"
android:layout_marginLeft="5dp"
android:layout_marginStart="5dp"
android:layout_marginRight="30dp"
android:layout_marginEnd="30dp"
android:layout_toRightOf="@id/art_work"
android:layout_toEndOf="@+id/art_work"
android:singleLine="true"
/>
<RelativeLayout
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="20dp"
android:layout_marginLeft="5dp"
android:layout_marginStart="5dp"
android:layout_marginRight="30dp"
android:layout_marginEnd="30dp"
android:layout_marginBottom="10dp"
android:layout_toRightOf="@+id/art_work"
android:layout_toEndOf="@id/art_work"
android:layout_below="@id/Name">
<TextView
android:id="@+id/duration"
android:textSize="12sp"
android:textColor="#000"
android:layout_width="wrap_content"
android:layout_alignParentStart="true"
android:layout_alignParentLeft="true"
android:layout_height="20dp"
android:singleLine="true"
android:gravity="clip_horizontal"
android:ellipsize="end"/>
<TextView
android:id="@+id/artist"
android:textSize="12sp"
android:textColor="#000"
android:layout_toRightOf="@+id/duration"
android:layout_toEndOf="@+id/duration"
android:layout_alignParentEnd="true"
android:layout_alignParentRight="true"
android:layout_width="wrap_content"
android:gravity="fill_horizontal"
android:layout_height="20dp"
android:singleLine="true" />
</RelativeLayout>
</RelativeLayout>
</FrameLayout>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/holder"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"
android:layout_centerVertical="true"
android:background="@android:color/transparent">
<Button
android:id="@+id/dots"
android:layout_width="40dp"
android:textStyle="bold"
android:background="?android:attr/selectableItemBackground"
android:layout_height="70dp"
android:text="@string/vertical_ellipsis"
android:textSize="25sp" />
</FrameLayout>
</RelativeLayout>