我知道周围有类似的问题，但所有答案都是针对这些应用程序的。请帮忙。 这是我遇到问题的活动的代码
public class MainActivity extends Activity implements OnClickListener
{
private static final int SWIPE_MIN_DISTANCE = 120;
private static final int SWIPE_MAX_OFF_PATH = 250;
private static final int SWIPE_THRESHOLD_VELOCITY = 200;
ViewFlipper flipper;
private GestureDetector gestureDetector;
static View passedView;
static String folderName = "myOffice";
static String folderPath = Environment.getExternalStorageDirectory() + "/" + folderName;
@SuppressWarnings("deprecation")
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
flipper = (ViewFlipper)findViewById(R.id.viewFlipper1);
flipper.setOnClickListener(this);
Button button1_1 = (Button)findViewById(R.id.button1_1);
button1_1.setOnClickListener(this);
Button button1_2 = (Button)findViewById(R.id.button1_2);
button1_2.setOnClickListener(this);
Button button3 = (Button)findViewById(R.id.button3);
button3.setOnClickListener(this);
Button newDoc = (Button)findViewById(R.id.newDoc);
newDoc.setOnClickListener(this);
listTest();
gestureDetector = new GestureDetector(new MyGestureDetector());
View mainview = (View) findViewById(R.id.viewFlipper1);
// Set the touch listener for the main view to be our custom gesture listener
mainview.setOnTouchListener(new View.OnTouchListener() {
public boolean onTouch(View v, MotionEvent event)
{
if (gestureDetector.onTouchEvent(event))
{
return true;
}
return false;
}
});
}
public static void checkForDirectory()
{
File folder = new File(folderPath);
if (folder.exists() == false)
{
folder.mkdir();
}
}
public String[] getFiles()
{
String[] fileNames;
File f = new File(folderPath);
File[] files = f.listFiles();
if (files.length == 0)
{
return null;
}
else
{
fileNames = new String[files.length];
for (int i=0; i < files.length; i++)
{
fileNames[i] = files[i].getName();
}
return fileNames;
}
}
public void listTest()
{
final ListView listView;
String[] filesInFolder = getFiles();
listView = (ListView)findViewById(R.id.listView1);
listView.setAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, filesInFolder));
listView.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener()
{
@Override
public boolean onItemLongClick(AdapterView<?> arg0, View v, int position, long id)
{
TextView tv = (TextView)v;
String fName = (String) tv.getText();
File file = new File(folderPath, fName);
showDeletedToast();
return file.delete();
}
private void showDeletedToast()
{
Toast toast = Toast.makeText(getApplicationContext(), "File deleted, Will be removed from the list.", Toast.LENGTH_LONG);
toast.show();
}
});
listView.setOnItemClickListener(new AdapterView.OnItemClickListener()
{
public void onItemClick(AdapterView<?> parent, View v, int position, long id)
{
Intent intent = new Intent(getApplicationContext(), TextActivity.class);
startActivity(intent);
passedView = TextActivity.getView(v);
}
});
listView.setAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, filesInFolder));
}
@Override
public boolean onCreateOptionsMenu(Menu menu)
{
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
@Override
public void onClick(View v)
{
if (v.getId()== R.id.button1_1)
{
flipper.showNext();
}
else if(v.getId()== R.id.button1_2)
{
flipper.showNext();
flipper.showNext();
}
else if(v.getId()== R.id.newDoc)
{
Intent intent = new Intent(this, TextActivity.class);
startActivity(intent);
}
}
class MyGestureDetector extends SimpleOnGestureListener
{
@Override
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY)
{
if (Math.abs(e1.getY() - e2.getY()) > SWIPE_MAX_OFF_PATH)
{
return false;
}
// right to left swipe
if(e1.getX() - e2.getX() > SWIPE_MIN_DISTANCE && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY)
{
flipper.showNext();
MainActivity.this.overridePendingTransition(
R.anim.slide_in_right,
R.anim.slide_out_left
);
// left to right swipe
}
else if (e2.getX() - e1.getX() > SWIPE_MIN_DISTANCE && Math.abs(velocityX) > SWIPE_THRESHOLD_VELOCITY)
{
flipper.showPrevious();
MainActivity.this.overridePendingTransition(
R.anim.slide_in_left,
R.anim.slide_out_right
);
}
return false;
}
// It is necessary to return true from onDown for the onFling event to register
@Override
public boolean onDown(MotionEvent e) {
return true;
}
}
}
为什么会发生这种情况？如何解决这个问题？ LogCat输出：
11-19 22:55:58.730: E/AndroidRuntime(10964): FATAL EXCEPTION: main
11-19 22:55:58.730: E/AndroidRuntime(10964): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.illuminatiRN.myOffice/com.illuminatiRN.myOffice.MainActivity}: java.lang.NullPointerException
11-19 22:55:58.730: E/AndroidRuntime(10964): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1818)
11-19 22:55:58.730: E/AndroidRuntime(10964): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1834)
11-19 22:55:58.730: E/AndroidRuntime(10964): at android.app.ActivityThread.access$500(ActivityThread.java:122)
11-19 22:55:58.730: E/AndroidRuntime(10964): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1027)
11-19 22:55:58.730: E/AndroidRuntime(10964): at android.os.Handler.dispatchMessage(Handler.java:99)
11-19 22:55:58.730: E/AndroidRuntime(10964): at android.os.Looper.loop(Looper.java:132)
11-19 22:55:58.730: E/AndroidRuntime(10964): at android.app.ActivityThread.main(ActivityThread.java:4126)
11-19 22:55:58.730: E/AndroidRuntime(10964): at java.lang.reflect.Method.invokeNative(Native Method)
11-19 22:55:58.730: E/AndroidRuntime(10964): at java.lang.reflect.Method.invoke(Method.java:491)
11-19 22:55:58.730: E/AndroidRuntime(10964): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:844)
11-19 22:55:58.730: E/AndroidRuntime(10964): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:602)
11-19 22:55:58.730: E/AndroidRuntime(10964): at dalvik.system.NativeStart.main(Native Method)
11-19 22:55:58.730: E/AndroidRuntime(10964): Caused by: java.lang.NullPointerException
11-19 22:55:58.730: E/AndroidRuntime(10964): at java.util.Arrays$ArrayList.<init>(Arrays.java:47)
11-19 22:55:58.730: E/AndroidRuntime(10964): at java.util.Arrays.asList(Arrays.java:163)
11-19 22:55:58.730: E/AndroidRuntime(10964): at android.widget.ArrayAdapter.<init>(ArrayAdapter.java:128)
11-19 22:55:58.730: E/AndroidRuntime(10964): at com.illuminatiRN.myOffice.MainActivity.listTest(MainActivity.java:100)
11-19 22:55:58.730: E/AndroidRuntime(10964): at com.illuminatiRN.myOffice.MainActivity.onCreate(MainActivity.java:49)
11-19 22:55:58.730: E/AndroidRuntime(10964): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1050)
11-19 22:55:58.730: E/AndroidRuntime(10964): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1782)
答案 0 :(得分：2)
传递给String的 filesInFolder ArrayAdapter数组是null，它会抛出您在堆栈跟踪中看到的NullPointerException。确保此数组（ filesInFolder ）非空。当您从getFiles()方法返回该数组时，请对其进行修改，以便在files.length为0时返回空数组。