我的Android应用程序似乎无法启动。我在主要活动中做了一些代码更改，尝试启动它并在启动时崩溃。然后我删除了那些代码更改，它仍然无法启动。我找不到代码有什么问题，这是主要的活动：
public class MainActivity extends TabActivity implements OnClickListener {
Button doSomething;
TabHost tabHost;
ViewFlipper flipper;
ListView listview;
ListView listview2;
HttpResponse re;
String json;
JSONObject j;
ListAdapter adapter2;
/*==================*/
ListView lazyList;
LazyAdapter lazyAdapter;
/*==================*/
private static final String LOG_TAG = "App";
@SuppressWarnings({ "unchecked", "rawtypes" })
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
doSomething = (Button) findViewById(R.id.btn_do_something);
doSomething.setOnClickListener(this);
flipper = (ViewFlipper) findViewById(R.id.layout_tab_one);
listview = (ListView) findViewById(R.id.listview);
listview2 = (ListView) findViewById(R.id.listview2);
/*==================================*/
lazyList=(ListView)findViewById(R.id.lazylistview);
//@SuppressWarnings("unchecked")
ListAdapter adapter = new ArrayAdapter(this,android.R.layout.simple_list_item_1,this.fetch());
adapter2 = new ArrayAdapter(this,android.R.layout.simple_list_item_1,this.fetchList1());
listview.setAdapter(adapter);
listview2.setAdapter(adapter2);
flipper.setOnClickListener(this);
String tabname1 = getString(R.string.tabexample_tab1);
String tabname2 = getString(R.string.tabexample_tab2);
String tabname3 = getString(R.string.tabexample_tab3);
String tabname4 = getString(R.string.tabexample_tab4);
tabHost = getTabHost();
tabHost.addTab(tabHost.newTabSpec("tab1").setContent(R.id.layout_tab_one).setIndicator(tabname1));
tabHost.addTab(tabHost.newTabSpec("tab2").setContent(R.id.layout_tab_two).setIndicator(tabname2));
tabHost.addTab(tabHost.newTabSpec("tab3").setContent(R.id.layout_tab_three).setIndicator(tabname3));
tabHost.addTab(tabHost.newTabSpec("tab4").setContent(R.id.layout_tab_four).setIndicator(tabname4));
tabHost.setCurrentTab(0);
listview.setOnItemClickListener(new OnItemClickListener(){
public void onItemClick(AdapterView<?> a, View v, int position, long id) {
Object item = listview.getItemAtPosition(position);
SavePreferences("item",item.toString());
MainActivity.this.refreshList();
flipper.showNext();
}});
listview2.setOnItemClickListener(new OnItemClickListener(){
public void onItemClick(AdapterView<?> a, View v, int position, long id) {
flipper.showPrevious();
}});
lazyList.setOnItemClickListener(new OnItemClickListener(){
public void onItemClick(AdapterView<?> a, View v, int position, long id) {
flipper.showPrevious();
}});
}
public ArrayList<String> fetch()
{
ArrayList<String> listItems = new ArrayList<String>();
try {
URL twitter = new URL(
"JSON.php");
URLConnection tc = twitter.openConnection();
BufferedReader in = new BufferedReader(new InputStreamReader(
tc.getInputStream()));
String line;
while ((line = in.readLine()) != null) {
//make sure youe String line is completely filled after that..
if (!line.equals(null) && !line.equals("") && line.startsWith("["))
{
JSONArray jArray = new JSONArray(line);
Log.v(LOG_TAG,"jarray value: " + jArray);
for (int i = 0;i < jArray.length(); i++)
{
//SONObject jobj = jArray.getJSONObject(i);
String country = jArray.getString(i);
listItems.add(country);
// also make sure you get the value from the jsonObject using some key
// like, jobj.getString("country");
//istItems.add(jobj.getString(""));
}
}
}
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return listItems;
}
public ArrayList<String> fetchList1()
{
ArrayList<String> listItems = new ArrayList<String>();
try {
SharedPreferences sharedPreferences = getSharedPreferences("MY_SHARED_PREF", MODE_PRIVATE);
String selected = sharedPreferences.getString("item", "");
URL twitter = new URL(
"JSON2.php?item=" + selected);
URLConnection tc = twitter.openConnection();
BufferedReader in = new BufferedReader(new InputStreamReader(
tc.getInputStream()));
String line;
while ((line = in.readLine()) != null) {
//make sure youe String line is completely filled after that..
if (!line.equals(null) && !line.equals("") && line.startsWith("["))
{
JSONArray jArray = new JSONArray(line);
// Log.v(LOG_TAG,"jarray value: " + jArray);
for (int i = 0;i < jArray.length(); i++)
{
//SONObject jobj = jArray.getJSONObject(i);
String country = jArray.getString(i);
listItems.add(country);
// also make sure you get the value from the jsonObject using some key
// like, jobj.getString("country");
//istItems.add(jobj.getString(""));
}
}
}
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return listItems;
}
public ArrayList<String> fetchImages()
{
ArrayList<String> listItems = new ArrayList<String>();
try {
SharedPreferences sharedPreferences = getSharedPreferences("MY_SHARED_PREF", MODE_PRIVATE);
String selected = sharedPreferences.getString("item", "");
URL twitter = new URL(
"ImageJSON.php?item="+ selected);
Log.v(LOG_TAG,"URL**:" + twitter.toString());
URLConnection tc = twitter.openConnection();
BufferedReader in = new BufferedReader(new InputStreamReader(
tc.getInputStream()));
String line;
while ((line = in.readLine()) != null) {
//make sure youe String line is completely filled after that..
if (!line.equals(null) && !line.equals("") && line.startsWith("["))
{
JSONArray jArray = new JSONArray(line);
// Log.v(LOG_TAG,"jarray value: " + jArray);
for (int i = 0;i < jArray.length(); i++)
{
//SONObject jobj = jArray.getJSONObject(i);
String country = jArray.getString(i);
listItems.add(country);
// also make sure you get the value from the jsonObject using some key
// like, jobj.getString("country");
//istItems.add(jobj.getString(""));
}
}
}
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return listItems;
}
public ArrayList<String> fetchList2()
{
ArrayList<String> listItems = new ArrayList<String>();
try {
SharedPreferences sharedPreferences = getSharedPreferences("MY_SHARED_PREF", MODE_PRIVATE);
String selected = sharedPreferences.getString("item", "");
URL twitter = new URL(
"JSON3.php?item="+ selected);
URLConnection tc = twitter.openConnection();
BufferedReader in = new BufferedReader(new InputStreamReader(
tc.getInputStream()));
String line;
while ((line = in.readLine()) != null) {
//make sure youe String line is completely filled after that..
if (!line.equals(null) && !line.equals("") && line.startsWith("["))
{
JSONArray jArray = new JSONArray(line);
// Log.v(LOG_TAG,"jarray value: " + jArray);
for (int i = 0;i < jArray.length(); i++)
{
//SONObject jobj = jArray.getJSONObject(i);
String country = jArray.getString(i);
listItems.add(country);
// also make sure you get the value from the jsonObject using some key
// like, jobj.getString("country");
//istItems.add(jobj.getString(""));
}
}
}
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return listItems;
}
public void refreshList() {
/*adapter2 = null;
adapter2 = new ArrayAdapter(this,android.R.layout.simple_list_item_1,this.fetchList1());
listview2.setAdapter(adapter2);*/
lazyAdapter = null;
String[] imagesList = new String[this.fetchList1().size()];
imagesList = this.fetchImages().toArray(imagesList);
ArrayList<String> v = this.fetchList1();
ArrayList<String> t = this.fetchList2();
lazyAdapter=new LazyAdapter(this,imagesList,v,t);
lazyList.setAdapter(lazyAdapter);
//adapter2.notifyDatasetChanged();
}
private void SavePreferences(String key, String value){
SharedPreferences sharedPreferences = getSharedPreferences("MY_SHARED_PREF", MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPreferences.edit();
editor.putString(key, value);
editor.commit();
}
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
}
public void onBackPressed()
{
flipper.showPrevious();
}
}
这是清单;
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
android:versionCode="1"
android:versionName="1.0" package="com.myApp.android">
<application android:icon="@drawable/icon" android:label="@string/app_name">
<activity android:name=".MainActivity" android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".MainActivity" />
<activity android:name=".LazyAdapter" />
<activity android:name=".ImageLoader" />
</application>
<uses-sdk android:minSdkVersion="3"/>
<uses-permission
android:name="android.permission.INTERNET" />
</manifest>
Log Cat输出：
08-28 11:16:32.442: ERROR/AndroidRuntime(517): FATAL EXCEPTION: main
08-28 11:16:32.442: ERROR/AndroidRuntime(517): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.myApp.android/com.myApp.android.MainActivity}: java.lang.NullPointerException
08-28 11:16:32.442: ERROR/AndroidRuntime(517): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1748)
08-28 11:16:32.442: ERROR/AndroidRuntime(517): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1764)
08-28 11:16:32.442: ERROR/AndroidRuntime(517): at android.app.ActivityThread.access$1500(ActivityThread.java:122)
08-28 11:16:32.442: ERROR/AndroidRuntime(517): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1002)
08-28 11:16:32.442: ERROR/AndroidRuntime(517): at android.os.Handler.dispatchMessage(Handler.java:99)
08-28 11:16:32.442: ERROR/AndroidRuntime(517): at android.os.Looper.loop(Looper.java:132)
08-28 11:16:32.442: ERROR/AndroidRuntime(517): at android.app.ActivityThread.main(ActivityThread.java:4025)
08-28 11:16:32.442: ERROR/AndroidRuntime(517): at java.lang.reflect.Method.invokeNative(Native Method)
08-28 11:16:32.442: ERROR/AndroidRuntime(517): at java.lang.reflect.Method.invoke(Method.java:491)
08-28 11:16:32.442: ERROR/AndroidRuntime(517): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
08-28 11:16:32.442: ERROR/AndroidRuntime(517): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
08-28 11:16:32.442: ERROR/AndroidRuntime(517): at dalvik.system.NativeStart.main(Native Method)
08-28 11:16:32.442: ERROR/AndroidRuntime(517): Caused by: java.lang.NullPointerException
08-28 11:16:32.442: ERROR/AndroidRuntime(517): at com.android.MainActivity.onCreate(MainActivity.java:84)
08-28 11:16:32.442: ERROR/AndroidRuntime(517): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1048)
08-28 11:16:32.442: ERROR/AndroidRuntime(517): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1712)
答案 0 :(得分：1)
那是因为你有一个NullPointer。这一行doSomething = (Button) findViewById(R.id.btn_do_something);返回null。检查Button id是否真的是“btn_do_something”，或者是否有多个相同的ID分配给不同的按钮