问题
I have created an adopter to display images thumbnail of video form the specific folder but when I scroll it lags a little but why is that?
Below is the code:
Main activity class
public class TestvideolistingActivity extends ListActivity {
String filename = null;
String filePath = null;
String dirNameSlash = "/videotest/";
String dirName = "videotest";
String path = Environment.getExternalStorageDirectory() + dirNameSlash ;
String[] values;
String deleteFile ;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// getting the own adapter
getInit();
}
@Override
protected void onResume() {
getInit();
super.onResume();
}
public void getInit() {
deleteFile = null;
values = getFilesArrayFromSdCard();
setListAdapter(new MyAdapter(this, values));
}
protected void onListItemClick(ListView l, View v, int position, long id) {
String item = (String) getListAdapter().getItem(position);
Intent intentToPlayVideo = new Intent(Intent.ACTION_VIEW);
intentToPlayVideo.setDataAndType(Uri.parse(path + item), "video/*");
startActivity(intentToPlayVideo);
}
public String[] getFilesArrayFromSdCard() {
String[] fileList = null;
File videoFiles = new File(path);
if (videoFiles.isDirectory()) {
fileList = videoFiles.list();
}
return fileList;
}
}
this the adopter class which show;s the text and the thumbnail
public class MyAdapter extends ArrayAdapter<String> {
private final Activity context;
private final String[] names;
private String filePath = null;
private Bitmap bmThumbnail;
private String dateFormat = "dd/MM/yyyy HH:mm:ss";
private SimpleDateFormat formatter;
private String filename;
String dirNameSlash = "/videotest/";
static class ViewHolder {
// value for the name of the file
public TextView text;
// video file thumbnail
public ImageView image;
}
public MyAdapter(Activity context, String[] names) {
super(context, R.layout.rowlayout, names);
this.context = context;
this.names = names;
filePath = Environment.getExternalStorageDirectory() + dirNameSlash;
formatter = new SimpleDateFormat(dateFormat);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View rowView = convertView;
if (rowView == null) {
LayoutInflater inflater = context.getLayoutInflater();
rowView = inflater.inflate(R.layout.rowlayout, null);
ViewHolder viewHolder = new ViewHolder();
viewHolder.text = (TextView) rowView.findViewById(R.id.label);
viewHolder.image = (ImageView) rowView.findViewById(R.id.icon);
rowView.setTag(viewHolder);
}
ViewHolder holder = (ViewHolder) rowView.getTag();
// Video file name
String s = names[position];
holder.text.setText(s);
bmThumbnail = ThumbnailUtils.createVideoThumbnail(filename, Thumbnails.MICRO_KIND);
holder.image.setImageBitmap(bmThumbnail);
return rowView;
}
}
This is the error by using Akhil code
04-04 18:09:59.078: E/AndroidRuntime(10625): FATAL EXCEPTION: main
04-04 18:09:59.078: E/AndroidRuntime(10625): java.lang.IndexOutOfBoundsException: Invalid index 0, size is 0
04-04 18:09:59.078: E/AndroidRuntime(10625): at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:257)
04-04 18:09:59.078: E/AndroidRuntime(10625): at java.util.ArrayList.get(ArrayList.java:311)
04-04 18:09:59.078: E/AndroidRuntime(10625): at com.koders.testvideolisting.MyPerformanceArrayAdapter.getView(MyPerformanceArrayAdapter.java:111)
04-04 18:09:59.078: E/AndroidRuntime(10625): at android.widget.AbsListView.obtainView(AbsListView.java:1315)
04-04 18:09:59.078: E/AndroidRuntime(10625): at android.widget.ListView.makeAndAddView(ListView.java:1727)
04-04 18:09:59.078: E/AndroidRuntime(10625): at android.widget.ListView.fillDown(ListView.java:652)
04-04 18:09:59.078: E/AndroidRuntime(10625): at android.widget.ListView.fillFromTop(ListView.java:709)
04-04 18:09:59.078: E/AndroidRuntime(10625): at android.widget.ListView.layoutChildren(ListView.java:1580)
04-04 18:09:59.078: E/AndroidRuntime(10625): at android.widget.AbsListView.onLayout(AbsListView.java:1147)
04-04 18:09:59.078: E/AndroidRuntime(10625): at android.view.View.layout(View.java:7034)
04-04 18:09:59.078: E/AndroidRuntime(10625): at android.widget.FrameLayout.onLayout(FrameLayout.java:333)
04-04 18:09:59.078: E/AndroidRuntime(10625): at android.view.View.layout(View.java:7034)
04-04 18:09:59.078: E/AndroidRuntime(10625): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1249)
04-04 18:09:59.078: E/AndroidRuntime(10625): at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1125)
04-04 18:09:59.078: E/AndroidRuntime(10625): at android.widget.LinearLayout.onLayout(LinearLayout.java:1042)
04-04 18:09:59.078: E/AndroidRuntime(10625): at android.view.View.layout(View.java:7034)
04-04 18:09:59.078: E/AndroidRuntime(10625): at android.widget.FrameLayout.onLayout(FrameLayout.java:333)
04-04 18:09:59.078: E/AndroidRuntime(10625): at android.view.View.layout(View.java:7034)
04-04 18:09:59.078: E/AndroidRuntime(10625): at android.view.ViewRoot.performTraversals(ViewRoot.java:1049)
04-04 18:09:59.078: E/AndroidRuntime(10625): at android.view.ViewRoot.handleMessage(ViewRoot.java:1744)
04-04 18:09:59.078: E/AndroidRuntime(10625): at android.os.Handler.dispatchMessage(Handler.java:99)
04-04 18:09:59.078: E/AndroidRuntime(10625): at android.os.Looper.loop(Looper.java:144)
04-04 18:09:59.078: E/AndroidRuntime(10625): at android.app.ActivityThread.main(ActivityThread.java:4937)
04-04 18:09:59.078: E/AndroidRuntime(10625): at java.lang.reflect.Method.invokeNative(Native Method)
04-04 18:09:59.078: E/AndroidRuntime(10625): at java.lang.reflect.Method.invoke(Method.java:521)
04-04 18:09:59.078: E/AndroidRuntime(10625): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
04-04 18:09:59.078: E/AndroidRuntime(10625): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
04-04 18:09:59.078: E/AndroidRuntime(10625): at dalvik.system.NativeStart.main(Native Method)
回答1:
The listview is lagging because you are creating new Thumbnails in getView() every time. There is just no caching or re-use. As the use scrolls up/down , getView() is called and time consuming process of creating thumbnails happen, hence the lag. You will also run Out of Memory soon.
Create and keep an Array of Bitmaps, with the same length as the number of elements in the datasource and store your thumbnails in the array. Take out the bitmap from the array for that particular position inside getView(). This should considerably increase the performance.
EDIT I have added a Hasmap of bitmaps to demonstrate the re-use.
public MyAdapter(Activity context, String[] names) {
super(context, R.layout.rowlayout, names);
this.context = context;
this.names = names;
filePath = Environment.getExternalStorageDirectory() + dirNameSlash;
formatter = new SimpleDateFormat(dateFormat);
cacheBitmap = new HashMap<String, Bitmap>(names.length);
initCacheBitmap();
}
private void initCacheBitmap() {
for(String string:names)
cacheBitmap.put(string, ThumbnailUtils.createVideoThumbnail(filePath+string, Thumbnails.MICRO_KIND));
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View rowView = convertView;
if (rowView == null) {
LayoutInflater inflater = context.getLayoutInflater();
rowView = inflater.inflate(R.layout.rowlayout, null);
ViewHolder viewHolder = new ViewHolder();
viewHolder.text = (TextView) rowView.findViewById(R.id.label);
viewHolder.image = (ImageView) rowView.findViewById(R.id.icon);
rowView.setTag(viewHolder);
}
ViewHolder holder = (ViewHolder) rowView.getTag();
// Video file name
String s = names[position];
holder.text.setText(s);
holder.image.setImageBitmap(cacheBitmap.get(s));
return rowView;
}}
回答2:
Since you are creating Thumnail for video inside getView() it slow down your scrolling.
So you have to save your bitmap in Arrarys and list it i scroll.. Try this Sample for this will really helps you for fast scrolling. This Sample includes images , you have to change for Video in Media Content Providers. Fast Scroll Sample
来源：https://stackoverflow.com/questions/10005248/video-thumbnail-arrayadopter-is-slow-on-scroll