我一直试图在单击数据时将联系人数据从第二个活动的列表视图传递到我的主要活动的列表视图。但是，仅单击联系人按钮，该应用就会崩溃。我该如何解决？
MainActivity.java
package com.example.artist.sender;
import android.Manifest;
import android.app.AlertDialog;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.database.Cursor;
import android.net.Uri;
import android.os.Build;
import android.os.Parcelable;
import android.provider.ContactsContract;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.telephony.SmsManager;
import android.text.Editable;
import android.text.TextUtils;
import android.util.SparseBooleanArray;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
import org.w3c.dom.Text;
import java.util.ArrayList;
import java.util.List;
import static android.R.id.input;
import static android.app.AlertDialog.*;
public class MainActivity extends AppCompatActivity {
EditText itemText;
Button addButton;
Button sendText;
TextView text;
Button contact;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
itemText = (EditText) findViewById(R.id.editText);
addButton = (Button) findViewById(R.id.button1);
text=(TextView) findViewById(R.id.textView);
addButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if (TextUtils.isEmpty(itemText.getText())||(itemText.getText().length()<10)||(itemText.getText().length()>10)) {
itemText.setError("The number is not valid.");
return;
} else {
text.setText(itemText.getText().toString());
itemText.setText("");
return;
}
}
});
Button delete;
delete = (Button) findViewById(R.id.btn2);
delete.setOnClickListener(new AdapterView.OnClickListener() {
@Override
public void onClick(View view) {
int con=text.getLineCount();
if(con==0)
Toast.makeText(MainActivity.this, "No number available to delete", Toast.LENGTH_SHORT).show();
else
text.setText("");
}
});
sendText=(Button) findViewById(R.id.btn3);
sendText.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
String phoneno = text.getText().toString();
int count = text.getLineCount();
SmsManager smsMgrVar = SmsManager.getDefault();
if (count == 0) {
Toast.makeText(MainActivity.this, "No number available", Toast.LENGTH_SHORT).show();
}
else
if (ActivityCompat.checkSelfPermission(MainActivity.this, Manifest.permission.SEND_SMS) == PackageManager.PERMISSION_GRANTED)
{
try{
smsMgrVar.sendTextMessage(phoneno, null, "Hey There!", null, null);
Toast.makeText(MainActivity.this, "Message Sent",Toast.LENGTH_LONG).show();
}
catch (Exception ErrVar)
{
Toast.makeText(MainActivity.this, "Message Sending Failed", Toast.LENGTH_SHORT).show();
ErrVar.printStackTrace();
}
}
else
{
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M)
{
requestPermissions(new String[]{Manifest.permission.SEND_SMS}, 10);
}
}
}
});
contact =(Button) findViewById(R.id.btn4);
contact.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
{
startActivity(new Intent(MainActivity.this,contacts.class));
}
}
});
String tempholder=getIntent().getStringExtra("Listviewclickvalue");
text.setText(tempholder);
}
contacts.java
package com.example.artist.sender;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import java.util.ArrayList;
import android.annotation.TargetApi;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.ContentResolver;
import android.content.pm.PackageManager;
import android.database.Cursor;
import android.net.Uri;
import android.os.Build;
import android.os.Bundle;
import android.os.Handler;
import android.provider.ContactsContract;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
import static android.Manifest.permission.READ_CONTACTS;
public class contacts extends MainActivity {
private static final int REQUEST_READ_CONTACTS = 444;
private ListView mListView;
private ProgressDialog pDialog;
private Handler updateBarHandler;
ArrayList<String> contactList;
Cursor cursor;
int counter;
ListView list;
String temp;
TextView itemText;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.contacts);
pDialog = new ProgressDialog(contacts.this);
pDialog.setMessage("Reading contacts...");
pDialog.setCancelable(false);
pDialog.show();
mListView = (ListView) findViewById(R.id.list);
updateBarHandler = new Handler();
// Since reading contacts takes more time, let's run it on a separate thread.
new Thread(new Runnable() {
@Override
public void run() {
getContacts();
}
}).start();
// Set onclicklistener to the list item.
mListView.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
//TODO Do whatever you want with the list data
Toast.makeText(getApplicationContext(), "item clicked : \n" + contactList.get(position), Toast.LENGTH_SHORT).show();
}
});
}
private boolean mayRequestContacts() {
if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M) {
return true;
}
if (checkSelfPermission(READ_CONTACTS) == PackageManager.PERMISSION_GRANTED)
{
return true;
}
if (shouldShowRequestPermissionRationale(READ_CONTACTS)) {
requestPermissions(new String[]{READ_CONTACTS}, REQUEST_READ_CONTACTS);
} else {
requestPermissions(new String[]{READ_CONTACTS}, REQUEST_READ_CONTACTS);
}
return false;
}
/**
* Callback received when a permissions request has been completed.
*/
@Override
public void onRequestPermissionsResult(int requestCode, String[] permissions,
int[] grantResults) {
if (requestCode == REQUEST_READ_CONTACTS) {
if (grantResults.length == 1 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
getContacts();
}
}
}
public void getContacts() {
if (!mayRequestContacts()) {
return;
}
contactList = new ArrayList<String>();
String phoneNumber = null;
// String email = null;
Uri CONTENT_URI = ContactsContract.Contacts.CONTENT_URI;
String _ID = ContactsContract.Contacts._ID;
String DISPLAY_NAME = ContactsContract.Contacts.DISPLAY_NAME;
String HAS_PHONE_NUMBER = ContactsContract.Contacts.HAS_PHONE_NUMBER;
Uri PhoneCONTENT_URI = ContactsContract.CommonDataKinds.Phone.CONTENT_URI;
String Phone_CONTACT_ID = ContactsContract.CommonDataKinds.Phone.CONTACT_ID;
String NUMBER = ContactsContract.CommonDataKinds.Phone.NUMBER;
/* Uri EmailCONTENT_URI = ContactsContract.CommonDataKinds.Email.CONTENT_URI;
String EmailCONTACT_ID = ContactsContract.CommonDataKinds.Email.CONTACT_ID;
String DATA = ContactsContract.CommonDataKinds.Email.DATA;*/
StringBuffer output;
ContentResolver contentResolver = getContentResolver();
cursor = contentResolver.query(CONTENT_URI, null, null, null, null);
// Iterate every contact in the phone
if (cursor.getCount() > 0) {
counter = 0;
while (cursor.moveToNext()) {
output = new StringBuffer();
// Update the progress message
updateBarHandler.post(new Runnable() {
public void run() {
pDialog.setMessage("Reading contacts : " + counter++ + "/" + cursor.getCount());
}
});
String contact_id = cursor.getString(cursor.getColumnIndex(_ID));
String name = cursor.getString(cursor.getColumnIndex(DISPLAY_NAME));
int hasPhoneNumber = Integer.parseInt(cursor.getString(cursor.getColumnIndex(HAS_PHONE_NUMBER)));
if (hasPhoneNumber > 0) {
output.append("\n First Name:" + name);
//This is to read multiple phone numbers associated with the same contact
Cursor phoneCursor = contentResolver.query(PhoneCONTENT_URI, null, Phone_CONTACT_ID + " = ?", new String[]{contact_id}, null);
while (phoneCursor.moveToNext()) {
phoneNumber = phoneCursor.getString(phoneCursor.getColumnIndex(NUMBER));
output.append("\n Phone number:" + phoneNumber);
}
phoneCursor.close();
/* // Read every email id associated with the contact
Cursor emailCursor = contentResolver.query(EmailCONTENT_URI, null, EmailCONTACT_ID + " = ?", new String[]{contact_id}, null);
while (emailCursor.moveToNext()) {
email = emailCursor.getString(emailCursor.getColumnIndex(DATA));
output.append("\n Email:" + email);
}
emailCursor.close();
String columns[] = {
ContactsContract.CommonDataKinds.Event.START_DATE,
ContactsContract.CommonDataKinds.Event.TYPE,
ContactsContract.CommonDataKinds.Event.MIMETYPE,
};*/
String where = ContactsContract.CommonDataKinds.Event.TYPE + "=" + ContactsContract.CommonDataKinds.Event.TYPE_BIRTHDAY +
" and " + ContactsContract.CommonDataKinds.Event.MIMETYPE + " = '" + ContactsContract.CommonDataKinds.Event.CONTENT_ITEM_TYPE + "' and " + ContactsContract.Data.CONTACT_ID + " = " + contact_id;
String[] selectionArgs = null;
String sortOrder = ContactsContract.Contacts.DISPLAY_NAME;
/*Cursor birthdayCur = contentResolver.query(ContactsContract.Data.CONTENT_URI, columns, where, selectionArgs, sortOrder);
Log.d("BDAY", birthdayCur.getCount()+"");
if (birthdayCur.getCount() > 0) {
while (birthdayCur.moveToNext()) {
String birthday = birthdayCur.getString(birthdayCur.getColumnIndex(ContactsContract.CommonDataKinds.Event.START_DATE));
output.append("Birthday :" + birthday);
Log.d("BDAY", birthday);
}
}
birthdayCur.close();
}*/
// Add the contact to the ArrayList
contactList.add(output.toString());
}
// ListView has to be updated using a ui thread
runOnUiThread(new Runnable() {
@Override
public void run() {
ArrayAdapter<String> adapter = new ArrayAdapter<String>(getApplicationContext(), R.layout.contact_text, R.id.text1, contactList);
mListView.setAdapter(adapter);
}
});
// Dismiss the progressbar after 500 millisecondds
updateBarHandler.postDelayed(new Runnable() {
@Override
public void run() {
pDialog.cancel();
}
}, 500);
}
}
//passing the number to the mainactivity's textview through intent
list=(ListView) findViewById(R.id.list);
final String listview[] = new String[list.getCount()];
for (int j = 0; j < list.getCount(); j++) {
View v = list.getChildAt(j);
TextView tv = (TextView) v.findViewById(R.id.text1);
listview[j] = (String) tv.getText();
}
itemText = (TextView) findViewById(R.id.text1);
final String number = itemText.getText().toString();
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, android.R.id.text1, listview);
list.setAdapter(adapter);
list.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
if ((number.matches("[0-9]+"))&&(number.length()==10))
temp = listview[position].toString();
Intent intent = new Intent(contacts.this, MainActivity.class);
intent.putExtra("Listviewclickvalue", temp);
startActivity(intent);
}
}
);
}
logcat
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
at com.example.artist.sender.contacts.getContacts(contacts.java:236)
at com.example.artist.sender.contacts$1.run(contacts.java:57)
at java.lang.Thread.run(Thread.java:818)
这是错误的日志。它不断显示出findViewById一直在引用一个空对象，而我已经将所有变量都分配给了它们各自的ID。