我正在尝试在选项卡片段中的列表视图上实现延迟加载以加载数组 abc 的元素。我正在尝试加载 10 个元素，然后当用户向下滚动时，将加载接下来的 10 个元素。但是我的应用程序无法运行，因为我无法跳转到 UI 线程以对其进行更新（runonUithread(returnRes); 无法正常工作）。你能[请看下面的代码并提出正确的方法来实现延迟加载。谢谢你。
片段类：
package com.example.abe;
import java.util.ArrayList;
import android.annotation.TargetApi;
import android.app.Activity;
import android.content.Context;
import android.os.Build;
import android.os.Bundle;
import android.support.v4.app.ListFragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.ArrayAdapter;
import android.widget.ListView;
@TargetApi(Build.VERSION_CODES.HONEYCOMB)
public class Tab1Fragment extends ListFragment {
ListView lv;
Activity act = this.getActivity();
Context ct = this.getActivity();
XMLGettersSetters data;
boolean loadingMore = false;
String abc[] = new String[50];
static int count = 0;
int itemsPerPage = 10;
ArrayList<String> myListItems;
ArrayList<String> myListItems2;
ArrayAdapter<String> adapter;
static int size = 0;
@SuppressWarnings("unused")
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
if (container == null) {
return null;
}
myListItems2 = new ArrayList<String>();
adapter = new ArrayAdapter<String>(getActivity().getBaseContext(),
android.R.layout.simple_list_item_1, myListItems2);
View root = inflater.inflate(R.layout.tab_frag1_layout, container,
false);
lv = (ListView) root.findViewById(android.R.id.list);
lv.setAdapter(adapter);
return root;
}
@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
myListItems = new ArrayList<String>();
View footerView = ((LayoutInflater) this.getActivity()
.getSystemService(Context.LAYOUT_INFLATER_SERVICE)).inflate(
R.layout.listfooter, null, false);
this.getListView().addFooterView(footerView);
this.setListAdapter(adapter);
for (int i = 0; i < 50; i++) {
abc[i] = "ab" + i;
}
this.getListView().setOnScrollListener(new OnScrollListener() {
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
System.out.println(abc.length);
System.out.println(count);
int lastInScreen = firstVisibleItem + visibleItemCount;
System.out.println(lastInScreen);
if ((lastInScreen == totalItemCount) && !(loadingMore)) {
try {
Thread thread = new Thread(null, loadMoreListItems);
thread.start();
} catch (Exception e) {
e.printStackTrace();
}
}
}
});
try {
Thread thread = new Thread(null, loadMoreListItems);
thread.start();
} catch (Exception e) {
e.printStackTrace();
}
}
private Runnable loadMoreListItems = new Runnable() {
@Override
public void run() {
loadingMore = true;
myListItems = new ArrayList<String>();
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
}
size = abc.length;
for (int i = 0; i < itemsPerPage; i++) {
if (count < size) {
myListItems.add(abc[count].toString());
count = count + 1;
} else {
break;
}
}
Log.i("a", "b");
try {
act.runOnUiThread(returnRes);
} catch (Exception e) {
e.printStackTrace();
}
Log.i("a", "b");
}
};
private Runnable returnRes = new Runnable() {
@Override
public void run() {
if (myListItems != null && myListItems.size() > 0) {
for (int i = 0; i < myListItems.size(); i++)
adapter.add(myListItems.get(i));
}
lv.setAdapter(adapter);
Log.i("a", "b");
adapter.notifyDataSetChanged();
Log.i("a", "b");
loadingMore = false;
}
};
}
日志猫：
01-18 18:59:21.606: I/System.out(971): 50
01-18 18:59:21.606: I/System.out(971): 0
01-18 18:59:21.606: I/System.out(971): 0
01-18 18:59:21.926: I/System.out(971): 50
01-18 18:59:21.926: I/System.out(971): 0
01-18 18:59:21.926: I/System.out(971): 1
01-18 18:59:22.257: I/System.out(971): 50
01-18 18:59:22.257: I/System.out(971): 0
01-18 18:59:22.257: I/System.out(971): 1
01-18 18:59:22.676: I/a(971): b
01-18 18:59:22.676: W/System.err(971): java.lang.NullPointerException
01-18 18:59:22.715: W/System.err(971): at com.example.abe.Tab1Fragment$1.run(Tab1Fragment.java:113)
01-18 18:59:22.936: W/System.err(971): at java.lang.Thread.run(Thread.java:1019)
01-18 18:59:22.936: I/a(971): b
片段活动类：
package com.example.abe;
import java.util.HashMap;
import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentTransaction;
import android.view.View;
import android.widget.TabHost;
import android.widget.TabHost.TabContentFactory;
public class TabsFragmentActivity extends FragmentActivity implements
TabHost.OnTabChangeListener {
private TabHost mTabHost;
private HashMap<String, TabInfo> mapTabInfo = new HashMap<String, TabsFragmentActivity.TabInfo>();
private TabInfo mLastTab = null;
private class TabInfo {
private String tag;
private Class<?> clss;
private Bundle args;
private Fragment fragment;
TabInfo(String tag, Class<?> clazz, Bundle args) {
this.tag = tag;
this.clss = clazz;
this.args = args;
}
}
class TabFactory implements TabContentFactory {
private final Context mContext;
public TabFactory(Context context) {
mContext = context;
}
public View createTabContent(String tag) {
View v = new View(mContext);
v.setMinimumWidth(0);
v.setMinimumHeight(0);
return v;
}
}
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.tabs_layout);
initialiseTabHost(savedInstanceState);
if (savedInstanceState != null) {
mTabHost.setCurrentTabByTag(savedInstanceState.getString("tab")); // set
// the
// tab
// as
// per
// the
// saved
// state
}
}
protected void onSaveInstanceState(Bundle outState) {
outState.putString("tab", mTabHost.getCurrentTabTag()); // save the tab
// selected
super.onSaveInstanceState(outState);
}
private void initialiseTabHost(Bundle args) {
mTabHost = (TabHost) findViewById(android.R.id.tabhost);
mTabHost.setup();
TabInfo tabInfo = null;
TabsFragmentActivity.addTab(this, this.mTabHost, this.mTabHost
.newTabSpec("Tab1").setIndicator("ST"), (tabInfo = new TabInfo(
"Tab1", Tab1Fragment.class, args)));
this.mapTabInfo.put(tabInfo.tag, tabInfo);
TabsFragmentActivity.addTab(this, this.mTabHost, this.mTabHost
.newTabSpec("Tab2").setIndicator("CSI"),
(tabInfo = new TabInfo("Tab2", Tab2Fragment.class, args)));
this.mapTabInfo.put(tabInfo.tag, tabInfo);
this.onTabChanged("Tab1");
mTabHost.setOnTabChangedListener(this);
}
private static void addTab(TabsFragmentActivity activity, TabHost tabHost,
TabHost.TabSpec tabSpec, TabInfo tabInfo) {
tabSpec.setContent(activity.new TabFactory(activity));
String tag = tabSpec.getTag();
tabInfo.fragment = activity.getSupportFragmentManager()
.findFragmentByTag(tag);
if (tabInfo.fragment != null && !tabInfo.fragment.isDetached()) {
FragmentTransaction ft = activity.getSupportFragmentManager()
.beginTransaction();
ft.detach(tabInfo.fragment);
ft.commit();
activity.getSupportFragmentManager().executePendingTransactions();
}
tabHost.addTab(tabSpec);
}
public void onTabChanged(String tag) {
TabInfo newTab = this.mapTabInfo.get(tag);
if (mLastTab != newTab) {
FragmentTransaction ft = this.getSupportFragmentManager()
.beginTransaction();
if (mLastTab != null) {
if (mLastTab.fragment != null) {
ft.detach(mLastTab.fragment);
}
}
if (newTab != null) {
if (newTab.fragment == null) {
newTab.fragment = Fragment.instantiate(this,
newTab.clss.getName(), newTab.args);
ft.add(R.id.realtabcontent, newTab.fragment, newTab.tag);
} else {
ft.attach(newTab.fragment);
}
}
mLastTab = newTab;
ft.commit();
this.getSupportFragmentManager().executePendingTransactions();
}
}
}