信息：我是一个不错的java开发人员，我认为我很了解它，所以我决定给android一个机会，它对我来说并不是最顺利的道路。我经常搞砸了。无论如何，如果有人愿意帮我解决这个错误，我会非常感激！谢谢。
主类
package dev.shaw.MyShoppingPlanner;
import java.io.File;
import android.support.v7.app.ActionBarActivity;
import android.support.v4.app.Fragment;
import android.text.InputType;
import android.app.ActionBar;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.FragmentTransaction;
import android.app.ActionBar.Tab;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.EditText;
public class MainActivity extends ActionBarActivity {
private String m_Text = "";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final ActionBar actionbar = getActionBar();
actionbar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
if(firstTime()){
GenerateNeededFiles();
}
else{
//do nothing
}
ActionBar.TabListener tablistener = new ActionBar.TabListener() {
@Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
// TODO Auto-generated method stub
}
@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
switch(tab.getText().toString()){
case "Lists":
openLists();
break;
case "Store":
openStore();
case "Home":
openTab();
}
}
private void openTab() {
}
private void openStore() {
View v = new View(MainActivity.this);
v.setVisibility(1);
v.clearFocus();
v.bringToFront();
}
private void openLists() {
Intent intent = new Intent(MainActivity.this,List_Activity.class);
startActivity(intent);
}
@Override
public void onTabReselected(Tab tab, FragmentTransaction ft) {
// do nothing
}
};
actionbar.addTab(actionbar.newTab().setText("Home").setTabListener(tablistener));
actionbar.addTab(actionbar.newTab().setText("Store").setTabListener(tablistener));
actionbar.addTab(actionbar.newTab().setText("Lists").setTabListener(tablistener));
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment()).commit();
}
}
private boolean firstTime() {
File storelist = new File(this.getFilesDir() + "\\StoreList.txt");
File listnames = new File(this.getFilesDir() + "\\ListNames.txt");
if(storelist.exists() && listnames.exists()){
return false;
}
else{
return true;
}
}
private void GenerateNeededFiles() {
Intent intent = new Intent(MainActivity.this,Install_Activity.class);
startActivity(intent);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.main, menu);
return super.onCreateOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch(item.getItemId()){
case R.id.action_search:
openSearch();
return true;
case R.id.action_settings:
openSettings();
default:
return super.onOptionsItemSelected(item);
}
}
private void openSettings() {
}
private void openSearch() {
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("Search");
// Set up the input
final EditText input = new EditText(this);
// Specify the type of input expected; this, for example, sets the input as a password, and will mask the text
input.setInputType(InputType.TYPE_CLASS_TEXT);
builder.setView(input);
// Set up the buttons
builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
m_Text = input.getText().toString();
}
});
builder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
}
});
builder.show();
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container,
false);
return rootView;
}
}
}
调用
时出错的类package dev.shaw.MyShoppingPlanner;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;
import android.app.ListActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;
public class List_Activity extends ListActivity {
String ListNames[] = getListNames();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setListAdapter(new ArrayAdapter<String>(this, R.layout.singleitem , ListNames));
}
protected void onListItemClick(ListView lv, View v, int pos,long id){
this.onListItemClick(lv, v, pos, id);
ShoppingList list = new ShoppingList(ListNames[pos]);
try {
setListAdapter(new ArrayAdapter<String>(this, R.layout.singleitem, list.toArray(list.getFile())));
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
private String[] getListNames() {
File file = new File(this.getFilesDir() + "\\listnames.txt");
FileInputStream fis = null;
try {
fis = new FileInputStream(file);
} catch (FileNotFoundException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
InputStreamReader is = new InputStreamReader(fis);
BufferedReader br = new BufferedReader(is);
String line;
String names[] = new String[100];
int i = 0;
try {
while(true){
line = br.readLine();
if(line == null){
break;
}
else{
try{
names[i] = line;
}
catch(NullPointerException e){
e.printStackTrace();
}
i++;
}
}
} catch (IOException e) {
e.printStackTrace();
}
try {
br.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return names;
}
}
这是printStack
03-23 04:58:16.523: D/dalvikvm(3710): GC_FOR_ALLOC freed 151K, 18% free 2770K/3356K, paused 2ms, total 7ms
03-23 04:58:16.531: D/dalvikvm(3710): GC_FOR_ALLOC freed 100K, 19% free 2988K/3680K, paused 1ms, total 4ms
03-23 04:58:16.535: I/dalvikvm-heap(3710): Grow heap (frag case) to 4.414MB for 1127532-byte allocation
03-23 04:58:16.539: D/dalvikvm(3710): GC_FOR_ALLOC freed <1K, 15% free 4089K/4784K, paused 3ms, total 3ms
03-23 04:58:16.555: D/dalvikvm(3710): GC_FOR_ALLOC freed <1K, 15% free 4089K/4784K, paused 1ms, total 1ms
03-23 04:58:16.587: I/dalvikvm-heap(3710): Grow heap (frag case) to 6.833MB for 2536932-byte allocation
03-23 04:58:16.599: D/dalvikvm(3710): GC_FOR_ALLOC freed 0K, 10% free 6567K/7264K, paused 2ms, total 2ms
03-23 04:58:16.615: D/HardwareRenderer(3710): Profiling hardware renderer
03-23 04:58:16.647: D/libEGL(3710): loaded /system/lib/egl/libEGL_genymotion.so
03-23 04:58:16.651: D/(3710): HostConnection::get() New Host Connection established 0xb85b3b40, tid 3710
03-23 04:58:16.655: D/libEGL(3710): loaded /system/lib/egl/libGLESv1_CM_genymotion.so
03-23 04:58:16.655: D/libEGL(3710): loaded /system/lib/egl/libGLESv2_genymotion.so
03-23 04:58:16.711: W/EGL_genymotion(3710): eglSurfaceAttrib not implemented
03-23 04:58:16.711: E/OpenGLRenderer(3710): Getting MAX_TEXTURE_SIZE from GradienCache
03-23 04:58:16.723: E/OpenGLRenderer(3710): Getting MAX_TEXTURE_SIZE from Caches::initConstraints()
03-23 04:58:16.723: D/OpenGLRenderer(3710): Enabling debug mode 0
03-23 04:58:18.015: D/AndroidRuntime(3710): Shutting down VM
03-23 04:58:18.015: W/dalvikvm(3710): threadid=1: thread exiting with uncaught exception (group=0xa4bae648)
03-23 04:58:18.015: E/AndroidRuntime(3710): FATAL EXCEPTION: main
03-23 04:58:18.015: E/AndroidRuntime(3710): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{dev.shaw.MyShoppingPlanner/dev.shaw.MyShoppingPlanner.List_Activity}: java.lang.NullPointerException
03-23 04:58:18.015: E/AndroidRuntime(3710): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2137)
03-23 04:58:18.015: E/AndroidRuntime(3710): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
03-23 04:58:18.015: E/AndroidRuntime(3710): at android.app.ActivityThread.access$600(ActivityThread.java:141)
03-23 04:58:18.015: E/AndroidRuntime(3710): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
03-23 04:58:18.015: E/AndroidRuntime(3710): at android.os.Handler.dispatchMessage(Handler.java:99)
03-23 04:58:18.015: E/AndroidRuntime(3710): at android.os.Looper.loop(Looper.java:137)
03-23 04:58:18.015: E/AndroidRuntime(3710): at android.app.ActivityThread.main(ActivityThread.java:5103)
03-23 04:58:18.015: E/AndroidRuntime(3710): at java.lang.reflect.Method.invokeNative(Native Method)
03-23 04:58:18.015: E/AndroidRuntime(3710): at java.lang.reflect.Method.invoke(Method.java:525)
03-23 04:58:18.015: E/AndroidRuntime(3710): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
03-23 04:58:18.015: E/AndroidRuntime(3710): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
03-23 04:58:18.015: E/AndroidRuntime(3710): at dalvik.system.NativeStart.main(Native Method)
03-23 04:58:18.015: E/AndroidRuntime(3710): Caused by: java.lang.NullPointerException
03-23 04:58:18.015: E/AndroidRuntime(3710): at android.content.ContextWrapper.getFilesDir(ContextWrapper.java:199)
03-23 04:58:18.015: E/AndroidRuntime(3710): at dev.shaw.MyShoppingPlanner.List_Activity.getListNames(List_Activity.java:38)
03-23 04:58:18.015: E/AndroidRuntime(3710): at dev.shaw.MyShoppingPlanner.List_Activity.<init>(List_Activity.java:16)
03-23 04:58:18.015: E/AndroidRuntime(3710): at java.lang.Class.newInstanceImpl(Native Method)
03-23 04:58:18.015: E/AndroidRuntime(3710): at java.lang.Class.newInstance(Class.java:1130)
03-23 04:58:18.015: E/AndroidRuntime(3710): at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
03-23 04:58:18.015: E/AndroidRuntime(3710): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2128)
03-23 04:58:18.015: E/AndroidRuntime(3710): ... 11 more