我通过AsyncTask中的JSON数据填充项目对象并将其添加到ArrayList。我在onCreate活动方法中执行JSON类，之后我打印出ArrayList的大小为0.在JSON类onPostExecute方法中打印数据是好的，因此数据来自Web服务应该是这样。为什么在JSONParse执行后ArrayList仍然为空？
对不起，如果我忽略了一些基本的东西，我刚开始学习andorid。
public class StaggeredGridActivity extends Activity implements AbsListView.OnScrollListener, AbsListView.OnItemClickListener, AdapterView.OnItemLongClickListener {
private static final String TAG = "StaggeredGridActivity";
public static final String SAVED_DATA_KEY = "SAVED_DATA";
private StaggeredGridView mGridView;
private boolean mHasRequestedMore;
private SampleAdapter mAdapter;
//JSON FIELDS SETUP
//URL
String url = "http://.../web_services/get_items_test.php";
//JSON Node Names
private static final String TAG_ARRAY = "items";
private static final String TAG_ID = "id";
private static final String TAG_ITEMNAME = "iname";
private static final String TAG_NEWPRICE = "new_price";
private static final String TAG_STORENAME = "store_name";
private static final String TAG_CURR = "curr";
//JSON ARRAY
JSONArray items = null;
//ITEMS LIST
ArrayList<Item> item_list = new ArrayList<Item>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_sgv);
//Execute JSON
new JSONParse().execute();
//PRINTS OUT 0!
System.out.println(item_list.size());
setTitle("SGV");
mGridView = (StaggeredGridView) findViewById(R.id.grid_view);
//LayoutInflater layoutInflater = getLayoutInflater();
//View header = layoutInflater.inflate(R.layout.list_item_header_footer, null);
//View footer = layoutInflater.inflate(R.layout.list_item_header_footer, null);
//TextView txtHeaderTitle = (TextView) header.findViewById(R.id.txt_title);
//TextView txtFooterTitle = (TextView) footer.findViewById(R.id.txt_title);
//txtHeaderTitle.setText("THE HEADER!");
//txtFooterTitle.setText("THE FOOTER!");
//mGridView.addHeaderView(header);
//mGridView.addFooterView(footer);
mAdapter = new SampleAdapter(this, R.id.txt_line1, item_list);
// do we have saved data?
/*if (savedInstanceState != null) {
mData = savedInstanceState.getStringArrayList(SAVED_DATA_KEY);
}
*/
//if (mData == null) {
// mData = SampleData.generateSampleData();
//}
//
//for (String data : mData) {
//mAdapter.add(data);
//}
mGridView.setAdapter(mAdapter);
/*mGridView.setOnScrollListener(this);
mGridView.setOnItemClickListener(this);
mGridView.setOnItemLongClickListener(this);*/
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.menu_sgv_dynamic, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.col1:
mGridView.setColumnCount(1);
break;
case R.id.col2:
mGridView.setColumnCount(2);
break;
case R.id.col3:
mGridView.setColumnCount(3);
break;
}
return true;
}
/*@Override
protected void onSaveInstanceState(final Bundle outState) {
super.onSaveInstanceState(outState);
outState.putStringArrayList(SAVED_DATA_KEY, item_list);
}
*/
@Override
public void onScrollStateChanged(final AbsListView view, final int scrollState) {
Log.d(TAG, "onScrollStateChanged:" + scrollState);
}
@Override
public void onScroll(final AbsListView view, final int firstVisibleItem, final int visibleItemCount, final int totalItemCount) {
Log.d(TAG, "onScroll firstVisibleItem:" + firstVisibleItem +
" visibleItemCount:" + visibleItemCount +
" totalItemCount:" + totalItemCount);
// our handling
if (!mHasRequestedMore) {
int lastInScreen = firstVisibleItem + visibleItemCount;
if (lastInScreen >= totalItemCount) {
Log.d(TAG, "onScroll lastInScreen - so load more");
mHasRequestedMore = true;
// onLoadMoreItems();
}
}
}
/*private void onLoadMoreItems() {
final ArrayList<Item> item = JSONParse.execute();
for (String data : sampleData) {
mAdapter.add(data);
}
// stash all the data in our backing store
mData.addAll(sampleData);
// notify the adapter that we can update now
mAdapter.notifyDataSetChanged();
mHasRequestedMore = false;
}*/
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int position, long id) {
Toast.makeText(this, "Item Clicked: " + position, Toast.LENGTH_SHORT).show();
}
@Override
public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id)
{
Toast.makeText(this, "Item Long Clicked: " + position, Toast.LENGTH_SHORT).show();
return true;
}
/*****************************************JSON********************************************/
//GET JSON DATA FROM URL
private class JSONParse extends AsyncTask<String, String, JSONObject> {
JSONparser jParser = new JSONparser();
private JSONObject json;
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected JSONObject doInBackground(String... args) {
// Getting JSON from URL
json = jParser.getJSONFromUrl(url);
return json;
}
@Override
public void onPostExecute(JSONObject json) {
try {
// Getting JSON Array from URL
items = json.getJSONArray(TAG_ARRAY);
for(int i = 0; i < items.length(); i++){
JSONObject c = items.getJSONObject(i);
// Storing JSON item in a Variable
String id = c.getString(TAG_ID);
String itemname = c.getString(TAG_ITEMNAME);
String newprice = c.getString(TAG_NEWPRICE);
String storename = c.getString(TAG_STORENAME);
String curr = c.getString(TAG_CURR);
Item item = new Item();
item.setItemId(id);
item.setItemName(itemname);
item.setItemPrice(newprice);
item.setStoreName(storename);
item.setItemCurrency(curr);
item_list.add(item);
//This is good! It prints out all item names
System.out.println(item_list.get(i).getItemName());
}
} catch (JSONException e) {
e.printStackTrace();
}
}
}
}
答案 0 :(得分：1)
在行new JSONParse.execute()之后获取onCreate中的所有代码并将其放入函数中。在onPostExecute（）中调用该函数。
答案 1 :(得分：1)
new JSONParse().execute(); - 在后台完成，因此当您在System.out.println(item_list.size());方法中执行oncreate时，数据仍未下载...使用onPostExecute更新您的视图已经下载了数据...即加载适配器...您需要了解为什么要在AsyncTask中执行此操作。
达到此效果的目的，
@Override
public void onPostExecute(JSONObject json) {
try {
// Getting JSON Array from URL
items = json.getJSONArray(TAG_ARRAY);
for(int i = 0; i < items.length(); i++){
JSONObject c = items.getJSONObject(i);
// Storing JSON item in a Variable
String id = c.getString(TAG_ID);
String itemname = c.getString(TAG_ITEMNAME);
String newprice = c.getString(TAG_NEWPRICE);
String storename = c.getString(TAG_STORENAME);
String curr = c.getString(TAG_CURR);
Item item = new Item();
item.setItemId(id);
item.setItemName(itemname);
item.setItemPrice(newprice);
item.setStoreName(storename);
item.setItemCurrency(curr);
item_list.add(item);
//This is good! It prints out all item names
System.out.println(item_list.get(i).getItemName());
}
mAdapter = new SampleAdapter(this, R.id.txt_line1, item_list);
for (Item data : item_list) {
mAdapter.add(data);
}
mGridView.setAdapter(mAdapter);
} catch (JSONException e) {
e.printStackTrace();
}
答案 2 :(得分：0)
查询仍在执行，打印出来时结果尚未就绪。
拥有AsyncTask的onPostExecute()方法。在那里，您确定查询执行已完成，并且可以调用包含onCreate()方法中所有代码的函数。