Java .setOnClickListener 上的空指针异常
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Null pointer Exception on .setOnClickListener
提问by Hyman.Ramsden
I am having an issue with a click listener for a login modal submit button.
我遇到了登录模式提交按钮的单击侦听器问题。
This is the error.
这是错误。
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
I have a reasonable understanding of what a null pointer exception is and I have search thoroughly for an issue similar to mine. I have tried to reformat the click listener in several ways, made sure I have the correct view ID etc.
我对什么是空指针异常有一个合理的理解，并且我已经彻底搜索了与我类似的问题。我尝试以多种方式重新格式化点击侦听器，确保我拥有正确的视图 ID 等。
package...
import...
public class MainActivity extends ActionBarActivity implements NavigationDrawerFragment.NavigationDrawerCallbacks {
//Variables
String currentPage = "";
Stack<String> crumbs = new Stack<String>();
//Fragment managing the behaviors, interactions and presentation of the navigation drawer.
private NavigationDrawerFragment mNavigationDrawerFragment;
// Used to store the last screen title. For use in {@link #restoreActionBar()}.
public CharSequence mTitle;
//temp
AuthenticateUserTokenResult authenticateUserTokenResult;
String loginErrorMessage = "";
String loginErrorTitle = "";
Boolean logonSuccessful = false;
Dialog loginDialog;
// Login EditTexts
EditText Username;
EditText CompanyID;
EditText Password;
Button Submit;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mNavigationDrawerFragment = (NavigationDrawerFragment) getSupportFragmentManager().findFragmentById(R.id.navigation_drawer);
mTitle = getTitle(); // Set up the drawer.
mNavigationDrawerFragment.setUp(R.id.navigation_drawer, (DrawerLayout) findViewById(R.id.drawer_layout));
if(authenticateUserTokenResult == null) {
attemptLogin();
}
}
public void attemptLogin() {
loginDialog = new Dialog(this,android.R.style.Theme_Translucent_NoTitleBar);
loginDialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
loginDialog.setContentView(R.layout.login_modal);
loginDialog.setCancelable(false);
//loginDialog.setOnCancelListener(cancelListener);
loginDialog.show();
Submit = (Button)findViewById(R.id.Submit);
Submit.setOnClickListener(new View.OnClickListener() // the error is on this line (specifically the .setOnClickListener)
{
@Override
public void onClick(View v)
{
ClyxUserLogin user = new ClyxUserLogin();
Username = (EditText)findViewById(R.id.Username);
user.logon = Username.getText().toString();
CompanyID = (EditText)findViewById(R.id.CompanyID);
user.idCompany = Integer.parseInt(CompanyID.getText().toString());
Password = (EditText)findViewById(R.id.Password);
user.password = Password.getText().toString();
user.idApplication = 142;
authenticate(user);
}
});
}
There is more, obviously, but not relevant to the topic I think. Here is the XML file for the dialog that has the button on it.
显然，还有更多，但与我认为的主题无关。这是带有按钮的对话框的 XML 文件。
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#3366FF">
<RelativeLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:background="#FFFFFF" >
<TextView
android:id="@+id/LoginTitle"
android:layout_width="200dp"
android:layout_height="wrap_content"
android:gravity="center_horizontal"
android:layout_marginTop="10dp"
android:layout_marginStart="10dp"
android:textColor="#000000"
android:textSize="20sp"
android:text="Login" />
<EditText
android:id="@+id/Username"
android:layout_width="200dp"
android:layout_height="wrap_content"
android:layout_below="@+id/LoginTitle"
android:layout_margin="10dp"
android:hint="Username" />
<EditText
android:id="@+id/CompanyID"
android:layout_width="200dp"
android:layout_height="wrap_content"
android:layout_below="@+id/Username"
android:layout_alignStart="@+id/Username"
android:inputType="number"
android:hint="Company ID" />
<EditText
android:id="@+id/Password"
android:layout_width="200dp"
android:layout_height="wrap_content"
android:layout_below="@+id/CompanyID"
android:layout_alignStart="@+id/Username"
android:layout_marginTop="10dp"
android:layout_marginBottom="10dp"
android:inputType="textPassword"
android:hint="Password" />
<Button
android:id="@+id/Submit"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/Password"
android:layout_marginBottom="10dp"
android:layout_centerHorizontal="true"
android:text="Login" />
</RelativeLayout>
</RelativeLayout>
Any help would be greatly appreciated.
任何帮助将不胜感激。
采纳答案by 2Dee
Submitis nullbecause it is not part of activity_main.xml
Submit是null因为它不属于activity_main.xml
When you call findViewByIdinside an Activity, it is going to look for a Viewinside your Activity's layout.
当您findViewById在 an 内部调用时Activity，它会View在您的 Activity 布局中寻找 a 。
try this instead :
试试这个：
Submit = (Button)loginDialog.findViewById(R.id.Submit);
Another thing : you use
另一件事：你使用
android:layout_below="@+id/LoginTitle"
but what you want is probably
但你想要的可能是
android:layout_below="@id/LoginTitle"
See this questionabout the difference between @idand @+id.
见这个问题有关的区别@id和@+id。
回答by ρяσ?ρ?я K
android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' 在一个空对象引用上
Because Submitbutton is inside login_modalso you need to use loginDialogview to access button:
因为Submit按钮在里面login_modal所以你需要使用loginDialog视图来访问按钮：
Submit = (Button)loginDialog.findViewById(R.id.Submit);
回答by BenJaminSila
Try giving your Button in your main.xml a more descriptive name such as:
尝试给 main.xml 中的 Button 一个更具描述性的名称，例如：
<Button
android:id="@+id/buttonXYZ"
(use lowercase in your xml files, at least, the first letter)
（在您的 xml 文件中使用小写，至少是第一个字母）
And then in your MainActivity class, declare it as:
然后在您的 MainActivity 类中，将其声明为：
Button buttonXYZ;
Button buttonXYZ;
In your onCreate(Bundle savedInstanceState) method, define it as:
在您的 onCreate(Bundle savedInstanceState) 方法中，将其定义为：
buttonXYZ = (Button) findViewById(R.id.buttonXYZ);
Also, move the Buttons/TextViews outside and place them before the .setOnClickListener - it makes the code cleaner.
此外，将 Buttons/TextViews 移到外面并将它们放在 .setOnClickListener 之前 - 它使代码更清晰。
Username = (EditText)findViewById(R.id.Username);
CompanyID = (EditText)findViewById(R.id.CompanyID);
回答by Jose Kj
I too got similar error when i misplaced the code
当我放错代码时，我也遇到了类似的错误
text=(TextView)findViewById(R.id.text);// this line has to be below setcontentview
setContentView(R.layout.activity_my_otype);
//this is the correct place
text.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
}
});
I got it working on placing the code in right order as shown below
我开始按照正确的顺序放置代码，如下所示
setContentView(R.layout.activity_my_otype);
text=(TextView)findViewById(R.id.text);
text.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
}
});
