我正在尝试构建一个布局类似于新的Android Market，马赛克样式的活动，该活动列出了每个马赛克中的信息。当用户向左或向右滑动时，他们会看到越来越多的带有信息的马赛克。信息量是动态的，因为它是通过 AsyncTask 从 XML 文件加载的。
我决定使用 ViewPager/PagerAdapter 来处理视图和控制分页。每个页面都会有一个LinearLayout，类似于此链接中的图片：http: //dl.dropbox.com/u/4458251/mosaic.png
马赛克中的每个方块都是一个带有图像和文本视图的RelativeLayout。
我遇到的问题是显示的第一个视图始终为空白，当我尝试更改页面时，显示强制关闭错误。另外，当我调试时，我发现根本没有输入instantiateItem()方法PagesContentAdapter.java！是什么赋予了？。
这是我的活动（MosaicMenuActivity.java）：
public class MosaicMenuActivity extends Activity {
public final String TAG = "NoniusDroidBaseApp";
// The title image (on top of the window)
private String TITLE_IMAGE = "title/title_MAIN";
// The background (normally you don't want to change it)
private String BACKAGROUND_IMAGE = "background";
// The content loader is used to load the application on another thread
// It makes sure that you can't interact with the application until the load
// is completed,
// but it will also blocks allows you to exit the application while it it
// loading.
// The interface will also never block
private PageContentLoader content_loader;
// The content adapter holds one application content array.
private PagesContentAdapter content_adapter;
// Actual system language
private String language;
/*
* (non-Javadoc)
*
* @see android.app.Activity#onCreate(android.os.Bundle)
*/
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Apply the main.xml as the content view
setContentView(R.layout.main);
// Apply the Nonius default theme
getApplicationContext().setTheme(R.style.Theme);
}
@Override
public void onResume() {
super.onResume();
// Whenever the application resumes, the loader check if the Theme
// changed (or the language was modified)
// If it was modified, it loads the theme again
if (ThemeManager.themeModified(language)) {
loadTheme();
}
// Get the actual system language
language = SetTopBoxDetails.getLanguage();
// Build the content adapter
this.content_adapter = new PagesContentAdapter(
this.getApplicationContext(), language);
// Applies the content adapter to the content ViewPager
ViewPager myPager = (ViewPager) findViewById(R.id.scrollview_pages);
myPager.setAdapter(content_adapter);
myPager.setCurrentItem(0);
// Builds the module that will load the content from the xml
this.content_loader = new PageContentLoader(this, content_adapter, language);
// The content is read whenever the application resumes
loadDynamicContent();
}
public boolean onKeyDown(int keyCode, KeyEvent event){
Log.d(TAG, "onKeyDown");
return super.onKeyDown(keyCode, event);
}
/*
* This function is used to load content that comes from outside of the
* application.
*/
private void loadDynamicContent() {
// The content loader makes sure that the user can't interact with the
// application until the load is done.
this.content_loader.execute();
}
/*
* Loads the application theme.
*/
private void loadTheme() {
// Get the context
Context context = this.getApplicationContext();
// Load the background
RelativeLayout relativelayout_base = (RelativeLayout) findViewById(R.id.relativelayout_base);
relativelayout_base.setBackgroundDrawable(ThemeManager.getImage(
BACKAGROUND_IMAGE, context));
}
AsyncTask 是由我的PageContentLoader.java. 我从 XML 中获取所有数据，但未显示：
public class PageContentLoader extends AsyncTask<Void, Integer, Boolean> {
public static final String TAG = "PageContentLoader";
private static int SLEEPING_TIME = 2000;
// The location of the XML file
private static final String XML_PATH = "/data/nonius/menu/mosaic.xml";
// XML node keys used to parse xml
private static final String KEY_PAGE = "page";
private static final String KEY_PAGE_TEMPLATE = "template";
private static final String KEY_TILE = "tile";
// The parent activity. Used to lauch UI items
private MosaicMenuActivity activity;
// The content storage
private PagesContentAdapter content_adapter;
// The dialog that locks the user interaction
private LoaderDialog dialog;
// The array of content (in this demo, Pages!)
public ArrayList<Page> pages;
private String language;
public PageContentLoader(MosaicMenuActivity activity,
PagesContentAdapter content_adapter, String language) {
this.activity = activity;
this.pages = new ArrayList<Page>();
this.dialog = new LoaderDialog(this.activity);
this.content_adapter = content_adapter;
this.language = language;
}
public boolean loadXml() {
Log.d(TAG, "loadXml");
// Clean the pages array
this.pages = new ArrayList<Page>();
// Get the DOM element
Document doc = XmlHelper.getDomElement(XML_PATH);
// If the document is null
if (doc == null) {
// Return fail
return false;
}
// Get all the nodes with tag KEY_PAGE
NodeList page_nodelist = doc.getElementsByTagName(KEY_PAGE);
Log.d(TAG, "getElementsByTagName");
// looping through all item nodes <item>
for (int page_i = 0; page_i < page_nodelist.getLength(); page_i++) {
Page page = new Page();
Log.d(TAG, "Page " + page_i);
// Get the element of the node list
Element page_element = (Element) page_nodelist.item(page_i);
String page_template = page_element.getAttribute(KEY_PAGE_TEMPLATE);
page.setTemplate(page_template);
NodeList tile_nodelist = page_element
.getElementsByTagName(KEY_TILE);
for (int tile_i = 0; tile_i < tile_nodelist.getLength(); tile_i++){
// Create an empty tile
Tile tile = new Tile();
Element tile_element = (Element) tile_nodelist.item(tile_i);
tile.importXmlElement(tile_element);
page.addTile(tile);
Log.d(TAG, tile.toString());
}
this.pages.add(page);
}
// Everything went ok
return true;
}
protected void onPreExecute() {
this.dialog.setLoadMode(activity.getString(R.string.loading_message));
this.dialog.show();
}
protected Boolean doInBackground(Void... params) {
// Parse the xml file
return this.loadXml();
}
protected void onPostExecute(Boolean success) {
// If the loader succeeded
if (success) {
// Update the adapter
content_adapter.updateContent(pages);
// If the dialog is visible, hide it
if (dialog.isShowing()) {
dialog.dismiss();
}
}
// If the loader failed
else {
// Start the error dialog
dialog.setErrorMode(activity
.getString(R.string.loading_error_message));
}
}
}
PagerAdapter 在我的PageContentAdapter.java. 在进行一些调试之后，构造方法被成功调用，但创建页面内容的方法（instantiateItem()）从未被调用：
public class PagesContentAdapter extends PagerAdapter {
public static final String TAG = "PagesContentAdapter";
// The list context
private Context context;
// The content array
public ArrayList<Page> pages;
// The system language
private String language;
/**
* Class constructor
*
* @param context
* The context used to build the ouput views
*/
public PagesContentAdapter(Context context, String language) {
this.context = context;
// Create an empty pages array
this.pages = new ArrayList<Page>();
this.language = language;
}
/**
* Update the Adapter pages array and notify the parent
* that the data was modified
* @param pages
*/
public void updateContent(ArrayList<Page> pages) {
this.pages = pages;
//this.notifyDataSetChanged();
}
public int getCount() {
return pages.size();
}
public Object getItem(int position) {
return pages.get(position);
}
public long getItemId(int position) {
return position;
}
@Override
public void destroyItem(View collection, int position, Object view) {
((ViewPager) collection).removeView((View) view);
}
@Override
public void finishUpdate(View arg0) {
// TODO Auto-generated method stub
}
@Override
public Object instantiateItem(View page_view, int position) {
Page page = new Page();
page = pages.get(position);
LayoutInflater page_layout_inflater = (LayoutInflater) context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
LinearLayout linearlayout_page = (LinearLayout) page_layout_inflater.inflate(R.layout.page_template_5icons_v1, null);
for(int i=0; i<5; i++) {
linearlayout_page.addView(layoutTile(linearlayout_page, page, i));
}
((ViewPager) page_view).addView(linearlayout_page, 0);
return linearlayout_page;
}
public RelativeLayout layoutTile(LinearLayout linearlayout_page, Page page, int index) {
RelativeLayout relativelayout_tile = null;
switch(index) {
case 0: relativelayout_tile = (RelativeLayout) linearlayout_page.findViewById(R.id.item_big_1);
case 1: relativelayout_tile = (RelativeLayout) linearlayout_page.findViewById(R.id.item_small_1);
case 2: relativelayout_tile = (RelativeLayout) linearlayout_page.findViewById(R.id.item_small_2);
case 3: relativelayout_tile = (RelativeLayout) linearlayout_page.findViewById(R.id.item_small_3);
case 4: relativelayout_tile = (RelativeLayout) linearlayout_page.findViewById(R.id.item_small_4);
}
// Inflate it in a layout xml
LayoutInflater tile1_layout_inflater = (LayoutInflater) context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
tile1_layout_inflater.inflate(R.layout.tile, relativelayout_tile);
// Get the textview from the inflated layout
TextView textview_tail = (TextView) relativelayout_tile.findViewById(R.id.textview_tile);
Tile tile = page.getTiles().get(index);
// Set its text
textview_tail.setText(tile.getDescription());
return relativelayout_tile;
}
@Override
public boolean isViewFromObject(View view, Object object) {
return view == object;
}
@Override
public void restoreState(Parcelable arg0, ClassLoader arg1) {
// TODO Auto-generated method stub
}
@Override
public Parcelable saveState() {
// TODO Auto-generated method stub
return null;
}
@Override
public void startUpdate(View arg0) {
// TODO Auto-generated method stub
}
}
感谢我能得到的任何帮助。感谢您抽出宝贵时间查看此问题！