在我的应用程序中，我正在尝试操作EditText元素，但每次我尝试这样做时，它都会向我抛出nullPointerException。我不知道为什么会这样做，因为它似乎只发生在这个EditText，docTitle上，而不是我的任何其他人。
以下是抛出异常的java类的一部分：
public class MainActivity extends FragmentActivity implements RichText.EditTextImeBackListener, OnTouchListener, OnClickListener, TextWatcher{
private String[] drawerListViewItems1;
private String[] drawerListViewItems2;
private ArrayList<Editable> undoStrings;
private int undoIndex;
//this is the EditText that is giving me trouble, it is defined down in onCreate
public EditText docTitle;
private int styleStart;
private ListView drawerListView1;
private ListView drawerListView2;
private RelativeLayout formatBar;
private DrawerLayout drawerLayout;
private ActionBarDrawerToggle actionBarDrawerToggle;
private RichText richText;
private SaveFragment saveFragment;
private ToggleButton boldButton;
private ToggleButton emButton;
private ToggleButton uButton;
private ToggleButton strikeButton;
private boolean keyboardShown;
private boolean alreadyShown;
private boolean isMainContent;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//finds the left drawer
drawerListView1 = (ListView) findViewById(R.id.left_drawer);
//finds right drawer
drawerListView2 = (ListView)findViewById(R.id.right_drawer);
//loads the first drawer
loadDrawer1();
//loads the second drawer
loadDrawer2();
//finds the drawer layout
drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
//assign ActionBarDrawerToggle
actionBarDrawerToggle = new ActionBarDrawerToggle(this, drawerLayout, R.drawable.ic_drawer,
R.string.drawer_open, R.string.drawer_close);
//sets the drawer listener
drawerLayout.setDrawerListener(new DrawerLayout.SimpleDrawerListener() {
@Override
public void onDrawerOpened(View drawerLayout){
//hides format bar when a drawer is opened
if(keyboardShown){
hideFormatBarAnim();
}
}
@Override
public void onDrawerClosed(View drawerLayout){
//shows format bar when closed
showFormatBar();
}
});
//enable and show "up" arrow
getActionBar().setDisplayHomeAsUpEnabled(true);
// just styling option for the drawer layout
drawerLayout.setDrawerShadow(R.drawable.drawer_shadow, GravityCompat.START);
//item click listener for drawer items
drawerListView1.setOnItemClickListener(new DrawerItemClickListener());
drawerListView2.setOnItemClickListener(new DrawerItemClickListener());
isMainContent= true;
alreadyShown=false;
keyboardShown=false;
undoIndex=0;
undoStrings = new ArrayList<Editable>();
//assigns formatBar to its XML layout
formatBar = (RelativeLayout)findViewById(R.id.formatBar);
//assigns docTitle to its XML layout
docTitle = (EditText)findViewById(R.id.docTitle);
//This line here throws the error
docTitle.setText("Hello");
//defines save fragment
saveFragment = new SaveFragment();
//assigns richText to its XML layout and adds a TextChangeListener
richText= (RichText)findViewById(R.id.edit_text);
richText.addTextChangedListener(this);
//assigns boldButton to its XML layout and adds an OnClickListener
boldButton=(ToggleButton)findViewById(R.id.bold);
boldButton.setOnClickListener(this);
//assigns emButton to its XML layout and adds an OnClickListener
emButton=(ToggleButton)findViewById(R.id.ital);
emButton.setOnClickListener(this);
//assigns uButton to its XML layout and adds an OnClickListener
uButton=(ToggleButton)findViewById(R.id.underline);
uButton.setOnClickListener(this);
//assigns strikeButton to its XML layout and adds an onClickListener
strikeButton=(ToggleButton)findViewById(R.id.strike);
strikeButton.setOnClickListener(this);
//initiates sofKeyboardHook
softKeyboardHook();
//creates the default saving directory
Doc.makeDefaultDir();
lookForFiles();
}
以下是与之相关的XML布局：
<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#ffffff">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="400dp"
android:background="#1E772F"
android:layout_marginTop="350dp">
<EditText
android:id="@+id/docTitle"
android:text="DefaultDocName"
android:paddingTop="20dp"
android:layout_centerHorizontal="true"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="6dp"/>
<Button
android:id="@+id/save"
android:layout_height="wrap_content"
android:layout_width="150dp"
android:text="Save"
android:layout_below="@+id/docTitle"
android:layout_marginLeft="10dp"
android:layout_marginTop="20dp"
android:onClick="onSaveDoneClick"/>
<Button
android:id="@+id/cancel"
android:layout_height="wrap_content"
android:layout_width="150dp"
android:text="Cancel"
android:layout_marginLeft="20dp"
android:layout_marginTop="20dp"
android:layout_below="@+id/docTitle"
android:layout_toRightOf="@+id/save"
android:onClick="cancelSave"/>
</RelativeLayout>
</ScrollView>
继续发出错误的日志：
03-19 09:48:50.246 12996-12996/com.noahl98.jotmobile E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.noahl98.jotmobile, PID: 12996
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.noahl98.jotmobile/com.noahl98.jotmobile.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2190)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2250)
at android.app.ActivityThread.access$700(ActivityThread.java:139)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1411)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5083)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.noahl98.jotmobile.MainActivity.onCreate(MainActivity.java:133)
at android.app.Activity.performCreate(Activity.java:5260)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1110)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2154)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2250)
at android.app.ActivityThread.access$700(ActivityThread.java:139)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1411)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5083)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
at dalvik.system.NativeStart.main(Native Method)
提前感谢您的帮助。
答案 0 :(得分：2)
您要膨胀的布局称为＆＃39; activity_main.xml＆＃39;它似乎包含许多抽屉和其他不在你附加的布局文件中的东西。您确定不会混淆布局文件。
基本上看起来你没有'docTitle＆＃39;在＆＃39; activity_main.xml＆＃39;文件是这个原因
//assigns docTitle to its XML layout
docTitle = (EditText)findViewById(R.id.docTitle);
//This line here throws the error
docTitle.setText("Hello");
为您提供＆＃39; docTitle = null＆＃39;
答案 1 :(得分：0)
问题是你在onCreate函数中加载的布局不是具有editText的布局，
你可以检查：
setContentView(R.layout.activity_main);
这个activity_main布局是您发布的那个吗？
因为稍后在onCreate方法中使用的是drawerListView1，它不在您粘贴的XML中，而且不是null。
请确保：您正在使用的视图应该在您正在加载的布局中