在用户应该输入其凭据的 Activity 中，在 Activity 的“onCreate(...)”中，在 setContentView(layout) 之后，我正在这样做:
nameView = (EditText) findViewById(R.id.profileNameTextBox);
其中 nameView 是一个 EditText。当我尝试通过单击按钮从该变量获取文本时，我的应用程序崩溃了。其背后的原因是 nameView 持有一个空对象引用。我无法真正理解背后的原因，因为函数“findViewById(...)”返回对每个其他 View 对象(如 Button、Spinner、Image)的有效引用，但在调用 EditText 时返回 null。我已经多次重新检查了 ids，并交叉检查了几乎所有的小依赖项，用 google 搜索了很多，但无法真正找到解决方案或问题的原因。
底线是函数 findViewById 将 null 返回给一个对象，该对象显然存在于布局文件中，并且具有用于搜索的相同 id。
任何有关此问题的帮助都将不胜感激。
这是我的 Activity
package theappman.speedcontacts;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;
public class AddContact extends AppCompatActivity {
Contact currentContact;
private EditText nameView;
private EditText numberView;
private ImageView imageView;
private Spinner dayView;
private Spinner monthView;
private Spinner yearView;
private Button saveView;
private void loadViews(){
numberView = (EditText) findViewById(R.id.profileNumberTextBox);
imageView = (ImageView) findViewById(R.id.profileImage);
dayView = (Spinner) findViewById(R.id.dateSpinner);
monthView = (Spinner) findViewById(R.id.monthSpinner);
yearView = (Spinner) findViewById(R.id.yearSpinner);
saveView = (Button) findViewById(R.id.saveButton);
nameView = (EditText) findViewById(R.id.profileNameTextBox);
}
private void populateSpinners(){
String[] days = new String[32];
String[] months = new String[13];
String[] years = new String[71];
days[0] = "Day";
months[0] = "Month";
years[0] = "Year";
for (int i=1; i<32; i++){
days[i] = String.valueOf(i+1);
}
for (int i=1,j=69; i<71; i++,j--){
years[i] = String.valueOf(1947+j);
}
months[1] = "January";
months[2] = "February";
months[3] = "March";
months[4] = "April";
months[5] = "May";
months[6] = "June";
months[7] = "July";
months[8] = "August";
months[9] = "September";
months[10] = "October";
months[11] = "November";
months[12] = "December";
ArrayAdapter<String> dayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_dropdown_item, days);
dayView.setAdapter(dayAdapter);
ArrayAdapter<String> monthAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_dropdown_item, months);
monthView.setAdapter(monthAdapter);
ArrayAdapter<String> yearAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_dropdown_item, years);
yearView.setAdapter(yearAdapter );
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_add_contact);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
currentContact = new Contact();
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
// .setAction("Action", null).show();
}
});
loadViews();
populateSpinners();
saveView.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
if (nameView != null) {
String nnn = nameView.getText().toString();
Toast.makeText(AddContact.this, nnn,Toast.LENGTH_LONG).show();
}
Toast.makeText(AddContact.this, "not.",Toast.LENGTH_LONG).show();
}
});
}
public void saveContact(View view){
EditText t = (EditText) view.findViewById(R.id.profileNameTextBox);
String NAME = t.getText().toString();
//String NUMBER = view.findViewById(R.id.profileNumber).toString();
Toast.makeText(AddContact.this, "Ok.",Toast.LENGTH_LONG).show();
/*String DATE = day.getSelectedItem().toString() + "-" + month.getSelectedItem().toString() + "-" + year.getSelectedItem().toString();
if (NAME.equals("") || NUMBER.equals("") ){//|| day.getSelectedItem().toString().equals("Day") || month.getSelectedItem().toString().equals("Month") || year.getSelectedItem().toString().equals("Year")){
Toast.makeText(this, "Please fill all fields.",Toast.LENGTH_LONG).show();
return;
}*/
//currentContact.setName(NAME);
//currentContact.setNumber(NUMBER);
//currentContact.setDateOfBirth(DATE );
//save currentContact in database
/*Intent intent = getIntent();
intent.putExtra("key", "Contact Saved");
setResult(RESULT_OK, intent);
finish();*/
}
@Override
public void onBackPressed() {
nameView = (EditText) findViewById(R.id.profileNameTextBox);
Intent intent = getIntent();
intent.putExtra("key", nameView.getText().toString());
setResult(RESULT_OK, intent);
finish();
super.onBackPressed();
}
}
这些是我的布局文件
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context="theappman.speedcontacts.AddContact">
<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/AppTheme.AppBarOverlay">
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:popupTheme="@style/AppTheme.PopupOverlay" />
</android.support.design.widget.AppBarLayout>
<include layout="@layout/content_add_contact" />
<android.support.design.widget.FloatingActionButton
android:id="@+id/fab"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="bottom|end"
android:layout_margin="@dimen/fab_margin"
android:src="@android:drawable/ic_dialog_email" />
</android.support.design.widget.CoordinatorLayout>
上面的文件包含下面给出的代码
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:context="theappman.speedcontacts.AddContact"
tools:showIn="@layout/activity_add_contact">
<ImageView
android:id="@+id/profileImage"
android:src="@drawable/ic_person_black_48dp"
android:layout_width="match_parent"
android:layout_height="200dp" />
<Button
android:id="@+id/selectImageButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="right"
android:text="Select Picture"
/>
<EditText
android:name="@+id/profileNameTextBox"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="Enter Full Name"/>
<EditText
android:name="@+id/profileNumberTextBox"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:inputType="phone"
android:hint="Enter Phone Number"/>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="50dp"
android:layout_gravity="center"
android:orientation="horizontal"
android:weightSum="3"
>
<Spinner
android:layout_weight="1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:spinnerMode="dropdown"
android:id="@+id/dateSpinner"
/>
<Spinner
android:layout_weight="1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:spinnerMode="dropdown"
android:id="@+id/monthSpinner"/>
<Spinner
android:layout_weight="1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:spinnerMode="dropdown"
android:id="@+id/yearSpinner"/>
</LinearLayout>
<Button
android:id="@+id/saveButton"
android:layout_width="96dp"
android:layout_height="wrap_content"
android:text="Save"
android:layout_gravity="right"
/>
</LinearLayout>
最佳答案
您正在多个位置初始化profileNameTextBox。
在您正在使用的一个地方 -
EditText t = (EditText) view.findViewById(R.id.profileNameTextBox);
初始化profileNameTextBox。
从 saveContact()、onBackPressed() 和其他任何地方删除初始化。您应该只在 loadViews() 中初始化一次。就是这样。当你想访问它时，你可以使用nameView。
关于java - 无法在 'findViewById()' 之后使用 'setContentView()' 获取对 EditText 的引用，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/36923994/