我想当我点击特定的行时，文本应该被复制并粘贴到另一个活动中。我已经实现了代码，但是有一件事导致了空指针异常。请帮助我。
//@Override
// listening to single list item on click
listview.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// selected item
TextView text = (TextView) view.findViewById(R.id.title);
String lst_txt = text.getText().toString().trim();
System.out.println("Display text"+lst_txt );
// Launching new Activity on selecting single List Item
Intent i = new Intent(MainActivity.this, SingleListItem.class);
// sending data to new activity
i.putExtra("product",lst_txt );
startActivity(i);
}
});
//此处textView text=（textView）view.findViewByID（r.id.title）；导致空指针异常
洛卡特
12-12 07:41:25.459: E/AndroidRuntime(2326): FATAL EXCEPTION: main
12-12 07:41:25.459: E/AndroidRuntime(2326): java.lang.NullPointerException
12-12 07:41:25.459: E/AndroidRuntime(2326): at com.example.TwitterTutorial.MainActivity$1.onItemClick(MainActivity.java:70)
12-12 07:41:25.459: E/AndroidRuntime(2326): at android.widget.AdapterView.performItemClick(AdapterView.java:298)
12-12 07:41:25.459: E/AndroidRuntime(2326): at android.widget.AbsListView.performItemClick(AbsListView.java:1100)
12-12 07:41:25.459: E/AndroidRuntime(2326): at android.widget.AbsListView$PerformClick.run(AbsListView.java:2749)
12-12 07:41:25.459: E/AndroidRuntime(2326): at android.widget.AbsListView$1.run(AbsListView.java:3423)
12-12 07:41:25.459: E/AndroidRuntime(2326): at android.os.Handler.handleCallback(Handler.java:725)
12-12 07:41:25.459: E/AndroidRuntime(2326): at android.os.Handler.dispatchMessage(Handler.java:92)
12-12 07:41:25.459: E/AndroidRuntime(2326): at android.os.Looper.loop(Looper.java:137)
12-12 07:41:25.459: E/AndroidRuntime(2326): at android.app.ActivityThread.main(ActivityThread.java:5039)
12-12 07:41:25.459: E/AndroidRuntime(2326): at java.lang.reflect.Method.invokeNative(Native Method)
12-12 07:41:25.459: E/AndroidRuntime(2326): at java.lang.reflect.Method.invoke(Method.java:511)
12-12 07:41:25.459: E/AndroidRuntime(2326): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
12-12 07:41:25.459: E/AndroidRuntime(2326): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
12-12 07:41:25.459: E/AndroidRuntime(2326): at dalvik.system.NativeStart.main(Native Method)
主要活动
public class MainActivity extends ListActivity {
private ListActivity activity;
final static String ScreenName = "bane";
final static String LOG_TAG = "rnc";
ListView listview;
TextView text;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// setContentView(R.layout.twit_list);
// listView.setTextFilterEnabled(true);
activity = this;
listview = this.getListView();
downloadTweets();
listview.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
if(view != null && view.getContext() != null){
// selected item
//text = (TextView) view.findViewById(R.id.title);
// String lst_txt = text.getText().toString().trim();
String product = ((TextView) view.findViewById(R.id.targetmonths)).getText().toString();
//System.out.println("Text"+lst_txt );
// Launching new Activity on selecting single List Item
Intent i = new Intent(MainActivity.this, SingleListItem.class);
// sending data to new activity
i.putExtra("product",product );
startActivity(i);
}
}
// download twitter timeline after first checking to see if there is a network connection
public void downloadTweets() {
ConnectivityManager connMgr = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
if (networkInfo != null && networkInfo.isConnected()) {
new DownloadTwitterTask().execute(ScreenName);
} else {
Log.v(LOG_TAG, "No network connection available.");
}
}
// Uses an AsyncTask to download a Twitter user's timeline
private class DownloadTwitterTask extends AsyncTask<String, Void, String> {
final static String CONSUMER_KEY = "3GsPNkJacZedXIwoajycHzkkU";
final static String CONSUMER_SECRET = "kCsPxxjsfrwba4cSZWW0tmXvaIcWT6r5Gb2HD5VX3RDYoDGRfXG";
final static String TwitterTokenURL = "https://api.twitter.com/oauth2/token";
final static String TwitterStreamURL = "https://api.twitter.com/1.1/statuses/user_timeline.json?screen_name=";
@Override
protected String doInBackground(String... screenNames) {
String result = null;
if (screenNames.length > 0) {
result = getTwitterStream(screenNames[0]);
}
return result;
}
// onPostExecute convert the JSON results into a Twitter object (which is an Array list of tweets
@Override
protected void onPostExecute(String result) {
Twitter twits = jsonToTwitter(result);
// lets write the results to the console as well
for (Tweet tweet : twits) {
Log.i(LOG_TAG, tweet.getText());
}
// send the tweets to the adapter for rendering
ArrayAdapter<Tweet> adapter = new ArrayAdapter<Tweet>(activity, android.R.layout.simple_list_item_1, twits);
setListAdapter(adapter);
}
// converts a string of JSON data into a Twitter object
private Twitter jsonToTwitter(String result) {
Twitter twits = null;
if (result != null && result.length() > 0) {
try {
Gson gson = new Gson();
twits = gson.fromJson(result, Twitter.class);
} catch (IllegalStateException ex) {
// just eat the exception
}
}
return twits;
}
// convert a JSON authentication object into an Authenticated object
private Authenticated jsonToAuthenticated(String rawAuthorization) {
Authenticated auth = null;
if (rawAuthorization != null && rawAuthorization.length() > 0) {
try {
Gson gson = new Gson();
auth = gson.fromJson(rawAuthorization, Authenticated.class);
} catch (IllegalStateException ex) {
// just eat the exception
}
}
return auth;
}
private String getResponseBody(HttpRequestBase request) {
StringBuilder sb = new StringBuilder();
try {
DefaultHttpClient httpClient = new DefaultHttpClient(new BasicHttpParams());
HttpResponse response = httpClient.execute(request);
int statusCode = response.getStatusLine().getStatusCode();
String reason = response.getStatusLine().getReasonPhrase();
if (statusCode == 200) {
HttpEntity entity = response.getEntity();
InputStream inputStream = entity.getContent();
BufferedReader bReader = new BufferedReader(new InputStreamReader(inputStream, "UTF-8"), 8);
String line = null;
while ((line = bReader.readLine()) != null) {
sb.append(line);
}
} else {
sb.append(reason);
}
} catch (UnsupportedEncodingException ex) {
} catch (ClientProtocolException ex1) {
} catch (IOException ex2) {
}
return sb.toString();
}
private String getTwitterStream(String screenName) {
String results = null;
// Step 1: Encode consumer key and secret
try {
// URL encode the consumer key and secret
String urlApiKey = URLEncoder.encode(CONSUMER_KEY, "UTF-8");
String urlApiSecret = URLEncoder.encode(CONSUMER_SECRET, "UTF-8");
// Concatenate the encoded consumer key, a colon character, and the
// encoded consumer secret
String combined = urlApiKey + ":" + urlApiSecret;
// Base64 encode the string
String base64Encoded = Base64.encodeToString(combined.getBytes(), Base64.NO_WRAP);
// Step 2: Obtain a bearer token
HttpPost httpPost = new HttpPost(TwitterTokenURL);
httpPost.setHeader("Authorization", "Basic " + base64Encoded);
httpPost.setHeader("Content-Type", "application/x-www-form-urlencoded;charset=UTF-8");
httpPost.setEntity(new StringEntity("grant_type=client_credentials"));
String rawAuthorization = getResponseBody(httpPost);
Authenticated auth = jsonToAuthenticated(rawAuthorization);
// Applications should verify that the value associated with the
// token_type key of the returned object is bearer
if (auth != null && auth.token_type.equals("bearer")) {
// Step 3: Authenticate API requests with bearer token
HttpGet httpGet = new HttpGet(TwitterStreamURL + screenName);
// construct a normal HTTPS request and include an Authorization
// header with the value of Bearer <>
httpGet.setHeader("Authorization", "Bearer " + auth.access_token);
httpGet.setHeader("Content-Type", "application/json");
// update the results with the body of the response
results = getResponseBody(httpGet);
}
} catch (UnsupportedEncodingException ex) {
} catch (IllegalStateException ex1) {
}
return results;
}
}
}
用于显示ListView的XML文件
<?xml version="1.0" encoding="utf-8"?>
<ListView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@android:id/list"
android:layout_width="match_parent"
android:layout_height="wrap_content">
</ListView>
数据适配器
public class DataAdapter extends BaseAdapter {
Context mContext;
private LayoutInflater mInflater;
String targetmonths;
//String img;
//String targetamount;
String[] month;
//String[] year;
//String[] amount;
public DataAdapter(Context c, String[] month) {
this.month = month;
//this.year = year;
//this.amount = amount;
mContext = c;
mInflater = LayoutInflater.from(c);
}
public int getCount() {
return month.length;
}
public Object getItem(int position) {
return position;
}
public long getItemId(int position) {
return position;
}
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder = null;
if (convertView == null) {
convertView = mInflater.inflate(R.layout.customgrid, parent, false);
holder = new ViewHolder();
holder.month = (TextView) convertView
.findViewById(R.id.targetmonths);
//holder.img = (ImageView) convertView.findViewById(R.id.image_id);
// holder.amount = (TextView) convertView.findViewById(R.id.targetamount);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
try {
holder.month.setText(month[position]);
// holder.img.setImageResource(img[position]);
// holder.amount.setText(amount[position]);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return convertView;
}
static class ViewHolder {
TextView month;
// ImageView img;
// TextView year, amount;
}
}
自定义网格
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<TextView
android:id="@+id/targetmonths"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_gravity="left"
android:layout_weight="1"
android:gravity="left|center"
android:paddingBottom="5sp"
android:paddingLeft="10sp"
android:paddingRight="5sp"
android:paddingTop="5sp"
android:text="hello"
android:textColor="#ffffcc"
android:textSize="16sp">
</TextView>
</LinearLayout>
最佳答案
您获得npe是因为当您创建该listview的Adapter时，在这个布局中传递的android.R.layout.simple_list_item_1没有idTextView的title
所以像这样改变你的咬骨
//@Override
// listening to single list item on click
listview.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// selected item
String lst_txt = parent.getItemAtPosition(position).toString().trim();
System.out.println("Display text"+lst_txt );
// Launching new Activity on selecting single List Item
Intent i = new Intent(MainActivity.this, SingleListItem.class);
// sending data to new activity
i.putExtra("product",lst_txt );
startActivity(i);
}
});
Grep code for android.R.layout.simple_list_item_1
<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright (C) 2006 The Android Open Source Project
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
-->
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@android:id/text1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceListItemSmall"
android:gravity="center_vertical"
android:paddingStart="?android:attr/listPreferredItemPaddingStart"
android:paddingEnd="?android:attr/listPreferredItemPaddingEnd"
android:minHeight="?android:attr/listPreferredItemHeightSmall"
/>