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我在Activity中創建了一個Tabbed佈局。我的活動如下考慮點
1.選項卡數量取決於可用於源對象的排序類型。最多可以有三個標籤，即Top，Latest和Popular。
2.每個選項卡包含GridView，當IntentService獲取數據時應更新
3.用戶可以從工具欄中選擇源
4.選擇新的源時，選項卡的數量應該根據新的Source和GridView還應該更新相應在Tablayout中創建了一個gridview並嘗試用一個Intent服務更新Gridview
TabbedActivity
公共類TabbedActivity擴展AppCompatActivity {
private Toolbar toolbar;
private TabLayout tabLayout;
private ViewPager mViewPager;
private List<Source> allSourceItem;
private Context context;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_tabbed);
context = this;
// register broadcast
IntentFilter statusIntentFilter = new IntentFilter(Asset.ARTICLE_BROADCAST_ACTION);
TabbedActivity.ArticleStateReceiver mDownloadStateReceiver = new TabbedActivity.ArticleStateReceiver();
LocalBroadcastManager.getInstance(this).registerReceiver(mDownloadStateReceiver, statusIntentFilter);
// set toolbar
toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
// set tab layout
tabLayout = (TabLayout) findViewById(R.id.tab_layout);
// set the viewpager
mViewPager = (ViewPager) findViewById(R.id.container);
// set up page listner to viewpager
mViewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
@Override
public void onTabSelected(TabLayout.Tab tab) {
mViewPager.setCurrentItem(tab.getPosition());
}
@Override
public void onTabUnselected(TabLayout.Tab tab) {
}
@Override
public void onTabReselected(TabLayout.Tab tab) {
}
});
startSetUp(getRecentDisplayedData());
}
public void startSetUp(Source src){
int tabsCount = 3;
setTitle(src.getName());
tabsCount = getNumberOfTabs(src.getSortByAvailableTop(),src.getSortByAvailableLatest(),src.getSortByAvailablePopular());
setTabs(tabsCount);
tabLayout.setTabGravity(TabLayout.GRAVITY_FILL);
mViewPager.setAdapter(new SectionsPagerAdapter(getSupportFragmentManager(),tabsCount,src));
}
// handle menus of activity
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.menu_tabbed, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.action_settings) {
Intent intent = new Intent(this, SourcesActivity.class);
intent.putExtra("SOURCE_ACTIVITY_ACTION","TABBED");
startActivity(intent);
return true;
}
if(id == R.id.change_src){
//get all selected sources
allSourceItem = Source.getAll();
List<String> listItems = new ArrayList<String>();
for(int i = 0; i < allSourceItem.size(); i++){
listItems.add(allSourceItem.get(i).getName());
}
final CharSequence[] items = listItems.toArray(new CharSequence[listItems.size()]);
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle(R.string.chnage_news_source);
builder.setItems(items, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int item) {
Source.updateRecentDisplayed(allSourceItem.get(item));
restartActivity();
}
});
AlertDialog alert = builder.create();
alert.show();
}
return super.onOptionsItemSelected(item);
}
// for creatting tabs Fragments
public static class PlaceholderFragment extends Fragment {
/**
* The fragment argument representing the section number for this
* fragment.
*/
private GridView mGridView;
private ArticleAdapter mArticleAdapter;
private ArrayList<Article> mGridData = new ArrayList<Article>();
private TextView tv;
private static final String ARG_SECTION_NUMBER = "section_number";
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
public PlaceholderFragment() {
}
/**
* Returns a new instance of this fragment for the given section
* number.
*/
public static PlaceholderFragment newInstance(int sectionNumber) {
PlaceholderFragment fragment = new PlaceholderFragment();
Bundle args = new Bundle();
args.putInt(ARG_SECTION_NUMBER, sectionNumber);
fragment.setArguments(args);
return fragment;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_tabbed, container, false);
tv = (TextView) rootView.findViewById(R.id.test_tv);
tv.setText("Page counter :: "+getArguments().getInt(ARG_SECTION_NUMBER));
mGridView = (GridView) rootView.findViewById(R.id.article_grid);
update(mGridData);
return rootView;
}
public void update(ArrayList<Article> data){
mArticleAdapter = new ArticleAdapter(getContext(),R.layout.aricle_grid_element,data);
mGridView.setAdapter(mArticleAdapter);
}
}
public class SectionsPagerAdapter extends FragmentPagerAdapter {
int tabsCount;
Source src;
public SectionsPagerAdapter(FragmentManager fm, int tabsCount, Source src) {
super(fm);
this.tabsCount = tabsCount;
this.src = src;
}
@Override
public Fragment getItem(int position) {
// getItem is called to instantiate the fragment for the given page.
// Return a PlaceholderFragment (defined as a static inner class below).
if(position == 0){
runArticleService(position+1);
return PlaceholderFragment.newInstance(position + 1);
}else if (position == 1){
runArticleService(position+1);
return PlaceholderFragment.newInstance(position + 1);
}else if (position == 2){
runArticleService(position+1);
return PlaceholderFragment.newInstance(position + 1);
}
return null;
}
@Override
public int getCount() {
// Show 3 total pages.
return tabsCount;
}
@Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return "SECTION 1";
case 1:
return "SECTION 2";
case 2:
return "SECTION 3";
}
return null;
}
private void runArticleService(int tabNumber){
Intent mServiceIntent = new Intent(getBaseContext(), ArticleService.class);
mServiceIntent.setData(Uri.parse(Asset.getSourceArticleURL(src.getUniqueId(),tabNumber)));
startService(mServiceIntent);
}
}
// broadcast receivers handle
private class ArticleStateReceiver extends BroadcastReceiver
{
private ArticleStateReceiver() {
}
// Called when the BroadcastReceiver gets an Intent it's registered to receive
@Override
public void onReceive(Context context, Intent intent) {
String response = intent.getStringExtra(Asset.ARTICLE_EXTENDED_DATA_TYPE);
String sortType = intent.getStringExtra(Asset.ARTICLE_EXTENDED_DATA_SORT);
if(sortType.equals("TOP")){
SectionsPagerAdapter sectionsPagerAdapter = (SectionsPagerAdapter) mViewPager.getAdapter();
PlaceholderFragment placeholderFragment = (PlaceholderFragment) sectionsPagerAdapter.getItem(0);
placeholderFragment.update(Asset.getArticleObjectFromJSON(response.toString()));
}else if(sortType.equals("LATEST")){
SectionsPagerAdapter sectionsPagerAdapter = (SectionsPagerAdapter) mViewPager.getAdapter();
PlaceholderFragment placeholderFragment = (PlaceholderFragment) sectionsPagerAdapter.getItem(1);
placeholderFragment.update(Asset.getArticleObjectFromJSON(response.toString()));
}else if(sortType.equals("POPULAR")){
SectionsPagerAdapter sectionsPagerAdapter = (SectionsPagerAdapter) mViewPager.getAdapter();
PlaceholderFragment placeholderFragment = (PlaceholderFragment) sectionsPagerAdapter.getItem(2);
placeholderFragment.update(Asset.getArticleObjectFromJSON(response.toString()));
}
}
}
// Extra methods
private int getNumberOfTabs(boolean top, boolean latest, boolean popular){
if(top && latest && popular){
return 3;
}else if(top && latest && !popular){
return 2;
}else if(top && !latest && !popular){
return 1;
}else{
return 1;
}
}
private void setTabs(int tabCount){
tabLayout.removeAllTabs();
if(tabCount == 3){
tabLayout.addTab(tabLayout.newTab().setText(getString(R.string.tab_1_text)));
tabLayout.addTab(tabLayout.newTab().setText(getString(R.string.tab_2_text)));
tabLayout.addTab(tabLayout.newTab().setText(getString(R.string.tab_3_text)));
}
if(tabCount == 2){
tabLayout.addTab(tabLayout.newTab().setText(getString(R.string.tab_1_text)));
tabLayout.addTab(tabLayout.newTab().setText(getString(R.string.tab_2_text)));
}
if(tabCount == 1){
tabLayout.addTab(tabLayout.newTab().setText(getString(R.string.tab_1_text)));
}
}
private Source getRecentDisplayedData(){
Source src = Source.getRecentDisplayed();
if(src!=null){
return src;
}else{
src = Source.getRandom();
Source.updateRecentDisplayed(src);
return Source.getRecentDisplayed();
}
}
public void restartActivity(){
Intent myIntent = new Intent(this, TabbedActivity.class);
startActivity(myIntent);
finish();
}
}
IntentService
public class ArticleService extends IntentService {
public String responseStr = null;
public String urlStr = null;
public ArticleService() {
super("ArticleService");
}
@Override
protected void onHandleIntent(Intent intent) {
Uri url = intent.getData();
urlStr = url.toString();
responseStr = Asset.fetchSourceDataFromURL(urlStr);
sendBroadcast();
}
protected void sendBroadcast(){
Intent localIntent = new Intent(Asset.ARTICLE_BROADCAST_ACTION).putExtra(Asset.ARTICLE_EXTENDED_DATA_TYPE,responseStr);
if(urlStr.toLowerCase().contains(Asset.SORT_TOP_URL.toLowerCase())){
localIntent.putExtra(Asset.ARTICLE_EXTENDED_DATA_SORT,"TOP");
}else if (urlStr.toLowerCase().contains(Asset.SORT_LATEST_URL.toLowerCase())){
localIntent.putExtra(Asset.ARTICLE_EXTENDED_DATA_SORT,"LATEST");
}else if (urlStr.toLowerCase().contains(Asset.SORT_POPULAR_URL.toLowerCase())){
localIntent.putExtra(Asset.ARTICLE_EXTENDED_DATA_SORT,"POPULAR");
}
LocalBroadcastManager.getInstance(this).sendBroadcast(localIntent);
}
}
錯誤，我無法理解
01-26 07:57:29.789 1494-1494/in.co.yogender.newsnick.newsnick E/AndroidRuntime: FATAL EXCEPTION: main
Process: in.co.yogender.newsnick.newsnick, PID: 1494
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference
at android.view.LayoutInflater.from(LayoutInflater.java:232)
at android.widget.ArrayAdapter.<init>(ArrayAdapter.java:181)
at android.widget.ArrayAdapter.<init>(ArrayAdapter.java:166)
at in.co.yogender.newsnick.newsnick.Adapters.ArticleAdapter.<init>(ArticleAdapter.java:0)
at in.co.yogender.newsnick.newsnick.TabbedActivity$PlaceholderFragment.update(TabbedActivity.java:197)
at in.co.yogender.newsnick.newsnick.TabbedActivity$ArticleStateReceiver.onReceive(TabbedActivity.java:273)
at android.support.v4.content.LocalBroadcastManager.executePendingBroadcasts(LocalBroadcastManager.java:297)
at android.support.v4.content.LocalBroadcastManager.access$000(LocalBroadcastManager.java:46)
at android.support.v4.content.LocalBroadcastManager$1.handleMessage(LocalBroadcastManager.java:116)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
在此先感謝
請顯示ArticleAdapter.java。 –