调用saveDetails（）函数时，应用程序总是崩溃。不知道是什么主要原因。我弄清楚了。有人，请帮帮我。
当我删除saveDetails（）函数时，app会完美启动并在单击imageButton时调用contact_details布局。但是当添加该功能时，应用程序就会崩溃。该日志在saveButton.setOnClickListener（）上显示错误。
package com.bikram.contacts;
import android.database.Cursor;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageButton;
import android.widget.ListView;
import android.widget.Toast;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
DatabaseHelper databaseHelper;
EditText firstName, lastName, phoneNumber;
ImageButton imageButton;
Button saveButton;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
databaseHelper = new DatabaseHelper(this);
firstName = (EditText) findViewById(R.id.first_name);
lastName = (EditText) findViewById(R.id.last_name);
phoneNumber = (EditText) findViewById(R.id.phone_number);
imageButton = (ImageButton) findViewById(R.id.imageButton);
saveButton = (Button) findViewById(R.id.save_button);
viewName();
addContacts();
saveDetails();
}
public void saveDetails() {
saveButton.setOnClickListener(
new View.OnClickListener() {
@Override
public void onClick(View v) {
}
}
);
}
public void addContacts() {
imageButton.setOnClickListener(
new View.OnClickListener() {
@Override
public void onClick(View v) {
setContentView(R.layout.contact_details);
}
}
);
}
public void viewName() {
Cursor result = databaseHelper.getName();
ArrayList arrayList = new ArrayList();
while (result.moveToNext()) {
arrayList.add(result.getString(0));
arrayList.add(result.getString(1));
}
ArrayAdapter arrayAdapter = new ArrayAdapter(this, R.layout.text_view, arrayList);
ListView listView = (ListView) findViewById(R.id.display_full_name);
listView.setAdapter(arrayAdapter);
}
}
DatabaseHelper.java
package com.bikram.contacts;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
/**
* Created by Sabina on 13-Nov-16.
*/
public class DatabaseHelper extends SQLiteOpenHelper {
public static final String databaseName = "Contact.db";
public static final String tableName = "contact_details";
public static final String col_1 = "First Name";
public static final String col_2 = "Last Name";
public static final String col_3 = "Mobile Number";
public DatabaseHelper(Context context) {
super(context, databaseName, null, 4);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("Create table " + tableName + "(First Name Text, Last Name Text, Mobile Number Number Not Null Primary Key);");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("Drop table if exists" + tableName);
onCreate(db);
}
public Cursor getName() {
SQLiteDatabase db = this.getWritableDatabase();
String query = "Select First Name, Last Name from " + tableName;
Cursor result = db.rawQuery(query, null);
return result;
}
public boolean addContactDetails(String firstName, String lastName, String phoneNumber){
SQLiteDatabase db = this.getWritableDatabase();
ContentValues contentValues = new ContentValues();
contentValues.put(col_1, firstName);
contentValues.put(col_2, lastName);
contentValues.put(col_3, phoneNumber);
long result = db.insert(tableName, null, contentValues);
if(result == -1)
return false;
else
return true;
}
}
从android Monitor
登录11-13 18:27:49.343 2108-2108/com.bikram.contacts W/dalvikvm: threadid=1: thread exiting with uncaught exception (group=0x41fd7ce0)
11-13 18:27:49.343 2108-2108/com.bikram.contacts W/dalvikvm: threadid=1: uncaught exception occurred
11-13 18:27:49.344 2108-2108/com.bikram.contacts W/System.err: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.bikram.contacts/com.bikram.contacts.MainActivity}: java.lang.NullPointerException
11-13 18:27:49.345 2108-2108/com.bikram.contacts W/System.err: at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2347)
11-13 18:27:49.345 2108-2108/com.bikram.contacts W/System.err: at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2399)
11-13 18:27:49.345 2108-2108/com.bikram.contacts W/System.err: at android.app.ActivityThread.access$800(ActivityThread.java:160)
11-13 18:27:49.345 2108-2108/com.bikram.contacts W/System.err: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1330)
11-13 18:27:49.346 2108-2108/com.bikram.contacts W/System.err: at android.os.Handler.dispatchMessage(Handler.java:110)
11-13 18:27:49.346 2108-2108/com.bikram.contacts W/System.err: at android.os.Looper.loop(Looper.java:193)
11-13 18:27:49.346 2108-2108/com.bikram.contacts W/System.err: at android.app.ActivityThread.main(ActivityThread.java:5330)
11-13 18:27:49.346 2108-2108/com.bikram.contacts W/System.err: at java.lang.reflect.Method.invokeNative(Native Method)
11-13 18:27:49.346 2108-2108/com.bikram.contacts W/System.err: at java.lang.reflect.Method.invoke(Method.java:515)
11-13 18:27:49.346 2108-2108/com.bikram.contacts W/System.err: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:829)
11-13 18:27:49.347 2108-2108/com.bikram.contacts W/System.err: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:645)
11-13 18:27:49.347 2108-2108/com.bikram.contacts W/System.err: at dalvik.system.NativeStart.main(Native Method)
11-13 18:27:49.347 2108-2108/com.bikram.contacts W/System.err: Caused by: java.lang.NullPointerException
11-13 18:27:49.348 2108-2108/com.bikram.contacts W/System.err: at com.bikram.contacts.MainActivity.saveDetails(MainActivity.java:44)
11-13 18:27:49.348 2108-2108/com.bikram.contacts W/System.err: at com.bikram.contacts.MainActivity.onCreate(MainActivity.java:39)
11-13 18:27:49.348 2108-2108/com.bikram.contacts W/System.err: at android.app.Activity.performCreate(Activity.java:5264)
11-13 18:27:49.348 2108-2108/com.bikram.contacts W/System.err: at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1088)
11-13 18:27:49.348 2108-2108/com.bikram.contacts W/System.err: at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2311)
11-13 18:27:49.348 2108-2108/com.bikram.contacts W/System.err: ... 11 more
11-13 18:27:49.348 2108-2108/com.bikram.contacts W/dalvikvm: threadid=1: calling UncaughtExceptionHandler
11-13 18:27:49.350 2108-2108/com.bikram.contacts E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.bikram.contacts, PID: 2108
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.bikram.contacts/com.bikram.contacts.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2347)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2399)
at android.app.ActivityThread.access$800(ActivityThread.java:160)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1330)
at android.os.Handler.dispatchMessage(Handler.java:110)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:5330)
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:829)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:645)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.bikram.contacts.MainActivity.saveDetails(MainActivity.java:44)
at com.bikram.contacts.MainActivity.onCreate(MainActivity.java:39)
at android.app.Activity.performCreate(Activity.java:5264)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1088)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2311)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2399)
at android.app.ActivityThread.access$800(ActivityThread.java:160)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1330)
at android.os.Handler.dispatchMessage(Handler.java:110)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:5330)
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:829)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:645)
at dalvik.system.NativeStart.main(Native Method)
11-13 18:27:54.661 2108-2116/com.bikram.contacts D/dalvikvm: threadid=5: SuspendAll starting
11-13 18:27:54.661 2108-2116/com.bikram.contacts D/dalvikvm: threadid=5: threadid=1 status=7 sc=1 dc=0
11-13 18:27:54.661 2108-2116/com.bikram.contacts D/dalvikvm: threadid=5: threadid=11 status=7 sc=1 dc=0
11-13 18:27:54.661 2108-2116/com.bikram.contacts D/dalvikvm: threadid=5: threadid=10 status=7 sc=1 dc=0
11-13 18:27:54.661 2108-2116/com.bikram.contacts D/dalvikvm: threadid=5: threadid=9 status=7 sc=1 dc=0
11-13 18:27:54.661 2108-2116/com.bikram.contacts D/dalvikvm: threadid=5: threadid=8 status=4 sc=1 dc=0
11-13 18:27:54.661 2108-2116/com.bikram.contacts D/dalvikvm: threadid=5: threadid=7 status=4 sc=1 dc=0
11-13 18:27:54.661 2108-2116/com.bikram.contacts D/dalvikvm: threadid=5: threadid=6 status=4 sc=1 dc=0
11-13 18:27:54.661 2108-2116/com.bikram.contacts D/dalvikvm: threadid=5: threadid=4 status=8 sc=1 dc=0
11-13 18:27:54.661 2108-2116/com.bikram.contacts D/dalvikvm: threadid=5: threadid=3 status=8 sc=1 dc=0
11-13 18:27:54.661 2108-2116/com.bikram.contacts D/dalvikvm: threadid=5: threadid=2 status=8 sc=1 dc=0
11-13 18:27:54.661 2108-2116/com.bikram.contacts D/dalvikvm: threadid=5: SuspendAll complete : 1
11-13 18:27:54.661 2108-2116/com.bikram.contacts D/dalvikvm: threadid=5: ResumeAll starting
11-13 18:27:54.661 2108-2116/com.bikram.contacts D/dalvikvm: threadid=5: ResumeAll waking others
11-13 18:27:54.661 2108-2116/com.bikram.contacts D/dalvikvm: threadid=5: ResumeAll complete
activity_main.xml中
<RelativeLayout 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">
<ListView
android:id="@+id/display_full_name"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
<ImageButton
android:id="@+id/imageButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:layout_marginBottom="35dp"
android:layout_marginRight="25dp"
android:padding="5dp"
app:srcCompat="@mipmap/add_button" />
</RelativeLayout>
contact_details.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<TextView
android:id="@+id/textView2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="New Contact" />
<EditText
android:id="@+id/first_name"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10"
android:inputType="textPersonName" />
<EditText
android:id="@+id/last_name"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10"
android:inputType="textPersonName" />
<EditText
android:id="@+id/phone_number"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10"
android:inputType="phone" />
<Button
android:id="@+id/save_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:elevation="12dp"
android:text="Save" />
</LinearLayout>
text_view.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id = "@+id/textView"/>
</LinearLayout>
答案 0 :(得分：3)
您尝试在同一活动中使用两种布局。 activity_main.xml已加载onCreate，但它不包含ID为Button的{{1}}。因此，当您致电save_button时，saveButton = (Button) findViewById(R.id.save_button);的结果值为saveButton。
稍后，在null中，您设置为在点击按钮时将活动的内容视图更改为addContacts。此布局包含contact_details，其ID为Button，但您不能再次调用save_button，因此findViewById变量仍为saveButton。即使你这样做了，问题仍然会出现，因为崩溃发生在点击按钮之前。
您发现崩溃的原因是因为在调用null后，您继续调用addContacts方法，该方法会尝试在saveDetails变量上调用方法。如上所述，变量包含saveButton，因此NPE和崩溃。
我建议不要在单个活动中使用多个内容视图。考虑创建一个新活动来处理联系人详细信息条目，并在按下添加按钮时启动它。如果您不想为此使用活动，则可以轻松地使用片段。
答案 1 :(得分：0)
您必须在activity_main.xml中包含contact_details。上面的@clownba0t已经解释了原因。