我开发了一个联系人应用程序。它完成了普通联系人应用程序应该做的所有事情。总是有改进的机会。我在 Android Emulator 中注意到，当用户安顿下来后，开始加载联系人图像，他已将联系人列表滚动到有可能获得他正在搜索的联系人的区域。因此，我尝试在我的应用程序副本上实现相同的功能。我已经实施了。它的运行非常非常缓慢。正如我推测的那样，我相信应用程序正在多次运行线程，即使它已经检索了导致大滞后的图像。我知道 ASync 任务，但只是出于好奇并检查它是否可以完成，我不想在这里实现它。这是 MainActivity 的源代码。
package com.example.contact;
import java.io.InputStream;
import java.util.ArrayList;
import android.net.Uri;
import android.os.Bundle;
import android.provider.ContactsContract;
import android.provider.ContactsContract.Contacts;
import android.app.ListActivity;
import android.content.ContentUris;
import android.content.Context;
import android.database.Cursor;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.widget.AbsListView;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.ListView;
public class MainActivity extends ListActivity {
ListView listview;
private boolean mPaused;
private MyAdapter mAdapter;
private View view;
private boolean running = false;
final private ArrayList<String> con_ids = new ArrayList<String>();
private Context context;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
listview = getListView();
context = this;
Cursor c = getContentResolver().query(ContactsContract.Contacts.CONTENT_URI,
null,
null,
null,
ContactsContract.Contacts.DISPLAY_NAME+" ASC");
if(c!=null)
{
for(c.moveToFirst();!c.isAfterLast();c.moveToNext()){
con_ids.add(c.getString(c.getColumnIndex(ContactsContract.Contacts._ID)));
}
}
mAdapter = new MyAdapter(this, android.R.layout.simple_list_item_1, con_ids);
listview.setAdapter(mAdapter);
listview.setOnScrollListener(makeScrollListener());
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
public void setEnabled(boolean enabled) {
mPaused = !enabled;
}
private AbsListView.OnScrollListener makeScrollListener() {
return new AbsListView.OnScrollListener() {
@Override
public void onScrollStateChanged(AbsListView absListView, int scrollState) {
setEnabled(scrollState != AbsListView.OnScrollListener.SCROLL_STATE_TOUCH_SCROLL);
running = false;
}
@Override
public void onScroll(AbsListView absListView, int i, int i1, int i2) {
String log = "";
Log.d(log, "Scroll First Item" + i);
Log.d(log, ""+ listview.getChildCount());
final int want = i;
running = true;
runOnUiThread(new Thread(new Runnable() {
int totalChild = listview.getChildCount();
int first = listview.getFirstVisiblePosition() - listview.getHeaderViewsCount();
int toRetrieve = want-first;
int id;
long con_id;
Bitmap thumbnail;
final ListView list = listview;
@Override
public void run() {
// TODO Auto-generated method stub
while(running)
{
if(!(toRetrieve<0||toRetrieve>=totalChild))
{
id = want+toRetrieve;
con_id = Long.valueOf(con_ids.get(id));
Uri ContactUri = ContentUris.withAppendedId(Contacts.CONTENT_URI, con_id);
InputStream stream = ContactsContract.Contacts.openContactPhotoInputStream(context.getContentResolver(), ContactUri);
thumbnail = BitmapFactory.decodeStream(stream);
if(thumbnail == null)
{
toRetrieve++;
continue;
}
else
{
View view = list.getChildAt(toRetrieve);
if(view == null)
{
toRetrieve++;
continue;
}
else
{
ImageView iamge = (ImageView) view.findViewById(R.id.contact_iamge);
iamge.setImageBitmap(thumbnail);
}
toRetrieve++;
}
}
else
{
running = false;
}
}
}
}));
}
};
}
}
MyAdapter 的代码，
package com.example.contact;
import java.util.ArrayList;
import android.content.ContentUris;
import android.content.Context;
import android.database.Cursor;
import android.graphics.drawable.Drawable;
import android.net.Uri;
import android.provider.ContactsContract;
import android.provider.ContactsContract.Contacts;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.webkit.WebView.FindListener;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
public class MyAdapter extends ArrayAdapter<String> {
private Context context;
private ListView listview;
private ArrayList<String> ids;
private LayoutInflater infl;
private String displayname;
private String maindetail;
private SimplifiedContact contact;
private Drawable drawable;
public MyAdapter(Context context, int ResourceId, ArrayList<String> list)
{
super(context, ResourceId, list);
this.context = context;
ids = list;
infl = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
drawable = context.getResources().getDrawable(R.drawable.person);
}
static class ViewHolder
{
public ImageView image;
public TextView display_name;
public TextView main_detail;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View row = convertView;
contact = new SimplifiedContact(context, Long.valueOf(ids.get(position)));
if(row == null)
{
row = infl.inflate(R.layout.single_cell, parent, false);
ViewHolder viewHolder = new ViewHolder();
viewHolder.display_name =(TextView) row.findViewById(R.id.disp_name);
viewHolder.main_detail = (TextView) row.findViewById(R.id.main_detail);
viewHolder.image = (ImageView)row.findViewById(R.id.contact_iamge);
row.setTag(viewHolder);
}
ViewHolder holder = (ViewHolder) row.getTag();
holder.display_name.setText(contact.getDisplayName());
holder.main_detail.setText(contact.getMainDetail());
holder.image.setBackgroundDrawable(drawable);
return row;
}
}
我想知道，如何减少这种滞后。提前致谢。