所以你能告诉我为什么我得到空指针exeptcion。 我正在检查asyncTask是否结束，然后将文本从编辑文本转到arryList之后按钮单击按钮inovks方法myclickhandler1（povijest）并将意图发送到secondActivity，你能告诉我我在这里做错了吗
MainActivity.java
private static final String DEBUG_TAG = "HttpExample";
private EditText urlText;
private TextView textView;
public int numOfTasks = 0;
private ArrayList<String> arrayList;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
urlText = (EditText) findViewById(R.id.myurl);
textView = (TextView) findViewById(R.id.mytext);
textView.setMovementMethod(ScrollingMovementMethod.getInstance());
arrayList = new ArrayList<String>();
}
public void myClickHandler(View view) {
String stringUrl = urlText.getText().toString();
ConnectivityManager connMgr = (ConnectivityManager)
getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
if (networkInfo != null && networkInfo.isConnected()) {
new DownloadWebpageTask().execute(stringUrl);
} else {
textView.setText("No network connection available.");
}
}
public class DownloadWebpageTask extends AsyncTask<String, Void, String> {
@Override
protected String doInBackground(String... urls) {
try {
return downloadUrl(urls[0]);
} catch (IOException e) {
return "Unable to retrieve web page. URL may be invalid.";
}
}
@Override
protected void onPreExecute()
{
addTask();
super.onPreExecute();
}
@Override
protected void onPostExecute(String result) {
textView.setText(result);
removeTask();
allTasksComplete();
}
}
private String downloadUrl(String myurl) throws IOException {
InputStream is = null;
try {
URL url = new URL(myurl);
HttpURLConnection connect = (HttpURLConnection) url.openConnection();
connect.setReadTimeout(10000 );
connect.setConnectTimeout(15000 );
connect.setRequestMethod("GET");
connect.setDoInput(true);
connect.connect();
int response = connect.getResponseCode();
Log.d(DEBUG_TAG, "The response is: " + response);
is = connect.getInputStream();
String contentAsString = readIt(is);
return contentAsString;
} finally {
if (is != null) {
is.close();
}
}
}
// Reads an InputStream and converts it to a String.
public String readIt(InputStream stream) throws IOException, UnsupportedEncodingException {
if (stream != null) {
StringBuilder sb = new StringBuilder();
String line;
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(stream, "UTF-8"));
while ((line = reader.readLine()) != null) {
sb.append(line);
}
} finally {
stream.close();
}
return sb.toString();
} else {
return "";
}
}
public void myClickHandler1(View povijest){
Intent intent = new Intent(MainActivity.this, SecondActivity.class);
intent.putStringArrayListExtra("arry_list", arrayList);
startActivity(intent);
;
}
public void addTask(){
numOfTasks++;
}
public void removeTask(){
numOfTasks--;
}
public void allTasksComplete()
{
if(numOfTasks ==0)
{
arrayList.add(urlText.getText().toString());
}
}
SecondActivity.java
package com.example.networking;
import java.util.ArrayList;
import android.support.v7.app.ActionBarActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ArrayAdapter;
import android.widget.ListView;
public class SecondActivity extends ActionBarActivity {
private ListView lv;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.secondactivity);
Intent i = getIntent();
ArrayList<String> list = i.getStringArrayListExtra("key");
lv = (ListView) findViewById(R.id.lista);
ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>( this, android.R.layout.simple_list_item_1, list );
lv.setAdapter(arrayAdapter);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.second, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
activity_main.xml中
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/LinearLayout1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.networking.MainActivity" >
<EditText
android:id="@+id/myurl"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:inputType="textWebEmailAddress"
android:ems="10" >
</EditText>
<TextView
android:id="@+id/mytext"
android:layout_width="200dp"
android:layout_height="0dp"
android:layout_marginLeft="38dp"
android:layout_marginTop="40dp"
android:layout_weight="0.17"
android:scrollbars="vertical" />
<Button
android:id="@+id/button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="start"
android:onClick="myClickHandler1"
android:text="POVIJEST" />
<Button
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="myClickHandler"
android:text="Download" />
</LinearLayout>
second_activity.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.networking.SecondActivity" >
<ListView
android:id="@+id/lista"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true" >
</ListView>
</RelativeLayout>
答案 0 :(得分：0)
使用arry_list代替key从意图中获取ArrayList：
ArrayList<String> list = i.getStringArrayListExtra("arry_list");
因为在MainActivity中，arry_list用作在intent中添加ArrayList但在SecondActivity Activity中尝试使用key获取ArrayList的键。