Android 我的活动已停止，显示空指针异常
当从一个活动移动到另一个活动时，它显示一个空指针异常，但我找不到错误发生的位置 在下面给出我的日志Android 我的活动已停止，显示空指针异常,android,android-intent,nullpointerexception,cursor,bundle,Android,Android Intent,Nullpointerexception,Cursor,Bundle,当从一个活动移动到另一个活动时，它显示一个空指针异常，但我找不到错误发生的位置 在下面给出我的日志 10-04 12:14:10.876: E/AndroidRuntime(1966): FATAL EXCEPTION: main 10-04 12:14:10.876: E/AndroidRuntime(1966): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.neochat/com.neoch
10-04 12:14:10.876: E/AndroidRuntime(1966): FATAL EXCEPTION: main
10-04 12:14:10.876: E/AndroidRuntime(1966): java.lang.RuntimeException: Unable to start
activity ComponentInfo{com.neochat/com.neochat.Displayfriendlist}:
java.lang.NullPointerException
10-04 12:14:10.876: E/AndroidRuntime(1966): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
10-04 12:14:10.876: E/AndroidRuntime(1966): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
10-04 12:14:10.876: E/AndroidRuntime(1966): at android.app.ActivityThread.access$600(ActivityThread.java:141)
10-04 12:14:10.876: E/AndroidRuntime(1966): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
10-04 12:14:10.876: E/AndroidRuntime(1966): at android.os.Handler.dispatchMessage(Handler.java:99)
10-04 12:14:10.876: E/AndroidRuntime(1966): at android.os.Looper.loop(Looper.java:137)
10-04 12:14:10.876: E/AndroidRuntime(1966): at android.app.ActivityThread.main(ActivityThread.java:5041)
10-04 12:14:10.876: E/AndroidRuntime(1966): at java.lang.reflect.Method.invokeNative(Native Method)
10-04 12:14:10.876: E/AndroidRuntime(1966): at java.lang.reflect.Method.invoke(Method.java:511)
10-04 12:14:10.876: E/AndroidRuntime(1966): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
10-04 12:14:10.876: E/AndroidRuntime(1966): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
10-04 12:14:10.876: E/AndroidRuntime(1966): at dalvik.system.NativeStart.main(Native Method)
10-04 12:14:10.876: E/AndroidRuntime(1966): Caused by: java.lang.NullPointerException
10-04 12:14:10.876: E/AndroidRuntime(1966): at com.neochat.LoginDataBaseAdapter.Displayfriend(LoginDataBaseAdapter.java:110)
10-04 12:14:10.876: E/AndroidRuntime(1966): at com.neochat.Displayfriendlist.onCreate(Displayfriendlist.java:25)
10-04 12:14:10.876: E/AndroidRuntime(1966): at android.app.Activity.performCreate(Activity.java:5104)
10-04 12:14:10.876: E/AndroidRuntime(1966): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
10-04 12:14:10.876: E/AndroidRuntime(1966): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
10-04 12:14:10.876: E/AndroidRuntime(1966): ... 11 more
public class DisplayFriendList extends Activity {
Context context = this;
LoginDataBaseAdapter Logi;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.displayfriend);
Logi = new LoginDataBaseAdapter(this);
Bundle data = getIntent().getExtras();
String code = data.getString("EMPCode");
String gotfriend = Logi.Displayfriend(code);
TextView txt = (TextView) findViewById(R.id.getfriend);
txt.setText(gotfriend);
Button btnadd = (Button) findViewById(R.id.data_addfriend);
btnadd.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
// Logi.insertFriendEntry(String Name, String Emp_Code);
Toast.makeText(context, "Friend added successfully",
Toast.LENGTH_SHORT).show();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// TODO Auto-generated method stub
return super.onCreateOptionsMenu(menu);
}
}
10-04 12:14:10.876: E/AndroidRuntime(1966): FATAL EXCEPTION: main
10-04 12:14:10.876: E/AndroidRuntime(1966): java.lang.RuntimeException: Unable to start
activity ComponentInfo{com.neochat/com.neochat.Displayfriendlist}:
java.lang.NullPointerException
10-04 12:14:10.876: E/AndroidRuntime(1966): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
10-04 12:14:10.876: E/AndroidRuntime(1966): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
10-04 12:14:10.876: E/AndroidRuntime(1966): at android.app.ActivityThread.access$600(ActivityThread.java:141)
10-04 12:14:10.876: E/AndroidRuntime(1966): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
10-04 12:14:10.876: E/AndroidRuntime(1966): at android.os.Handler.dispatchMessage(Handler.java:99)
10-04 12:14:10.876: E/AndroidRuntime(1966): at android.os.Looper.loop(Looper.java:137)
10-04 12:14:10.876: E/AndroidRuntime(1966): at android.app.ActivityThread.main(ActivityThread.java:5041)
10-04 12:14:10.876: E/AndroidRuntime(1966): at java.lang.reflect.Method.invokeNative(Native Method)
10-04 12:14:10.876: E/AndroidRuntime(1966): at java.lang.reflect.Method.invoke(Method.java:511)
10-04 12:14:10.876: E/AndroidRuntime(1966): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
10-04 12:14:10.876: E/AndroidRuntime(1966): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
10-04 12:14:10.876: E/AndroidRuntime(1966): at dalvik.system.NativeStart.main(Native Method)
10-04 12:14:10.876: E/AndroidRuntime(1966): Caused by: java.lang.NullPointerException
10-04 12:14:10.876: E/AndroidRuntime(1966): at com.neochat.LoginDataBaseAdapter.Displayfriend(LoginDataBaseAdapter.java:110)
10-04 12:14:10.876: E/AndroidRuntime(1966): at com.neochat.Displayfriendlist.onCreate(Displayfriendlist.java:25)
10-04 12:14:10.876: E/AndroidRuntime(1966): at android.app.Activity.performCreate(Activity.java:5104)
10-04 12:14:10.876: E/AndroidRuntime(1966): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
10-04 12:14:10.876: E/AndroidRuntime(1966): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
10-04 12:14:10.876: E/AndroidRuntime(1966): ... 11 more
public class DisplayFriendList extends Activity {
Context context = this;
LoginDataBaseAdapter Logi;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.displayfriend);
Logi = new LoginDataBaseAdapter(this);
Bundle data = getIntent().getExtras();
String code = data.getString("EMPCode");
String gotfriend = Logi.Displayfriend(code);
TextView txt = (TextView) findViewById(R.id.getfriend);
txt.setText(gotfriend);
Button btnadd = (Button) findViewById(R.id.data_addfriend);
btnadd.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
// Logi.insertFriendEntry(String Name, String Emp_Code);
Toast.makeText(context, "Friend added successfully",
Toast.LENGTH_SHORT).show();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// TODO Auto-generated method stub
return super.onCreateOptionsMenu(menu);
}
}
public String DisplayFriend(String Emp_Code) {
String displayfriend = "SELECT NAME , EMPLOYEE_CODE FROM EMPLOYEES " +
"WHERE " + " EMPLOYEE_CODE " + "LIKE '" +Emp_Code;
Cursor display = db.rawQuery(displayfriend, null);
String data = display.getString(0);
return data;
}
此行引发异常：
String gotfriend=Logi.Displayfriend（代码）因为Logi
var等于nullLogi
为空，因为它的初始化有问题，您应该检查Logi=new LoginDataBaseAdapter（此项）
和LoginDataBaseAdapter
的构造函数，以查看是否存在任何错误
如果您发布适配器的代码和第二个活动，我会尽量更精确
注意：您应该至少遵循“java良好实践”来命名方法和变量。非静态方法应以小写字母开头。非最终var应以小写字母开头。我认为问题在于DisplayFriend方法
在从游标中检索数据之前，请检查游标是否为null，如果为null，则通过异常检查它是否为null。我想这就是问题所在 哪一行是#110？如果是第一个（字符串显示…），则检查Emp_代码。如果是第三个（字符串数据…），则使用以下命令：
if (display==null) return null; //or ""
if (!display.moveToFirst()) return null;
//the rest of your code
解决此类错误的简单方法是查看日志cat
Displayfriend（LoginDataBaseAdapter.java:110）
双击这一行，您将被重定向到显示的行，根据代码，确定可能导致空指针的原因。要么对象未实例化，要么数据库不返回任何数据 检查此行字符串gotfriend=Logi.Displayfriend（代码）？哪一行是LoginDataBaseAdapter.java:110
？LoginDataBaseAdapter是另一个java类。Logi是objectpost类，用于从一个活动遍历到另一个活动。你在放额外的“EMPCode”吗在进入下一个活动之前，请确保Displayfriend方法中的db和display均不为null是的，我猜您不检查emp_代码是否为null，并且数据库中没有使用该emp_代码的数据，然后cursor在此处返回null您不检查cursor null或not如果cursor不为null，则您必须返回字符串。。！那么你的问题就解决了欢迎你把它变成固定的