アカウントの画像を表示するアプリを作っていtumblrます。一度に20枚の画像が表示され、下部には、押すと20枚の新しい画像がリストに読み込まれるというボットンがあります（新しい20枚の画像のみが表示されます）。AsyncTaskプロセスを実行するために使用しています。私はかなり遠くまで来ましたが、「もっと読み込む」ボタンをクリックすると、クラス内のNullPointerException行でアプリがクラッシュします。私は問題を見つけることができないようで、この時点で立ち往生しています。tumblrs.add(tumblr);DoInBackground
コードは次のようになります。
public class Example extends Activity {
ArrayList<Tumblr> tumblrs;
Context context = null;
ListView listView = null;
TextView footer;
int offset = 0;
ProgressDialog pDialog;
private String searchUrl = "http://api.tumblr.com/v2/blog/factsandchicks.com/posts?api_key=API_KEY&offset=0";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
ArrayList<Tumblr> tumblrs;
try {
tumblrs = getTumblrs();
listView = (ListView) findViewById(R.id.list);
View v = getLayoutInflater().inflate(R.layout.footer_layout, null);
footer = (TextView) v.findViewById(R.id.tvFoot);
listView.addFooterView(v);
listView.setAdapter(new UserItemAdapter(this, R.layout.listitem,
tumblrs));
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (JSONException e) {
e.printStackTrace();
}
footer.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
new loadMoreListView().execute();
}
});
}
public class UserItemAdapter extends ArrayAdapter<Tumblr> {
private ArrayList<Tumblr> tumblrs;
public UserItemAdapter(Context context, int imageViewResourceId,
ArrayList<Tumblr> tumblrs) {
super(context, imageViewResourceId, tumblrs);
this.tumblrs = tumblrs;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View v = convertView;
if (v == null) {
LayoutInflater vi = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
v = vi.inflate(R.layout.listitem, null);
}
Tumblr tumblr = tumblrs.get(position);
if (tumblr != null) {
ImageView image = (ImageView) v.findViewById(R.id.avatar);
if (image != null) {
image.setImageBitmap(getBitmap(tumblr.image_url));
}
}
return v;
}
}
public Bitmap getBitmap(String bitmapUrl) {
try {
URL url = new URL(bitmapUrl);
return BitmapFactory.decodeStream(url.openConnection()
.getInputStream());
} catch (Exception ex) {
return null;
}
}
public ArrayList<Tumblr> getTumblrs() throws ClientProtocolException,
IOException, JSONException {
searchUrl = "http://api.tumblr.com/v2/blog/factsandchicks.com/posts?api_key=API_KEY&offset=0";
ArrayList<Tumblr> tumblrs = new ArrayList<Tumblr>();
HttpClient client = new DefaultHttpClient();
HttpGet get = new HttpGet(searchUrl);
ResponseHandler<String> responseHandler = new BasicResponseHandler();
String responseBody = null;
try {
responseBody = client.execute(get, responseHandler);
} catch (Exception ex) {
ex.printStackTrace();
}
JSONObject jsonObject = new JSONObject(responseBody);
JSONArray posts = jsonObject.getJSONObject("response").getJSONArray(
"posts");
for (int i = 0; i < posts.length(); i++) {
JSONArray photos = posts.getJSONObject(i).getJSONArray("photos");
for (int j = 0; j < photos.length(); j++) {
JSONObject photo = photos.getJSONObject(j);
String url = photo.getJSONArray("alt_sizes").getJSONObject(0)
.getString("url");
Tumblr tumblr = new Tumblr(url);
tumblrs.add(tumblr);
}
}
return tumblrs;
}
public class Tumblr {
public String image_url;
public Tumblr(String url) {
this.image_url = url;
}
}
private class loadMoreListView extends AsyncTask<Void, Void, Void> {
@Override
protected void onPreExecute() {
// Showing progress dialog before sending http request
pDialog = new ProgressDialog(Example.this);
pDialog.setMessage("Please wait..");
pDialog.setIndeterminate(true);
pDialog.setCancelable(false);
pDialog.show();
}
@Override
protected Void doInBackground(Void... unused) {
// TODO Auto-generated method stub
runOnUiThread(new Runnable() {
public void run() {
// increment current page
offset += 20;
// Next page request
searchUrl = "http://api.tumblr.com/v2/blog/factsandchicks.com/posts?api_key=API_KEY&offset="
+ offset;
HttpClient client = new DefaultHttpClient();
HttpGet get = new HttpGet(searchUrl);
ResponseHandler<String> responseHandler = new BasicResponseHandler();
String responseBody = null;
try {
responseBody = client.execute(get, responseHandler);
} catch (Exception ex) {
ex.printStackTrace();
}
JSONObject jsonObject;
try {
jsonObject = new JSONObject(responseBody);
JSONArray posts = jsonObject.getJSONObject("response")
.getJSONArray("posts");
for (int i = 0; i < posts.length(); i++) {
JSONArray photos = posts.getJSONObject(i)
.getJSONArray("photos");
for (int j = 0; j < photos.length(); j++) {
JSONObject photo = photos.getJSONObject(j);
String url = photo.getJSONArray("alt_sizes")
.getJSONObject(0).getString("url");
Tumblr tumblr = new Tumblr(url);
tumblrs.add(tumblr);
}
}
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
// get listview current position - used to maintain scroll
// position
int currentPosition = listView.getFirstVisiblePosition();
// Setting new scroll position
listView.setSelectionFromTop(currentPosition + 1, 0);
}
});
return null;
}
protected void onPostExecute(Void unused) {
pDialog.dismiss();
}
}
}
ヘルプは非常に高く評価されています。