我是Android编程的新手，我已经搜索了我的眼睛，以解决我的问题，但我无法在任何地方找到它。我正在构建一个具有3种屏幕布局的应用程序，但我在最后一个屏幕上遇到了问题：
问题：
应用程序启动，2个第一个屏幕工作正常，但是当我转到最后一个屏幕（activity_katag.xml＆amp; katagActivity.java）并按“Deal1”时，应用程序停止并给我错误“不幸”，AppName“已停止了。“
LogCat错误文件：
03-12 13:32:12.270: W/dalvikvm(614): threadid=1: thread exiting with uncaught exception (group=0x40a122a0)
03-12 13:32:12.290: E/AndroidRuntime(614): FATAL EXCEPTION: main
03-12 13:32:12.290: E/AndroidRuntime(614): java.lang.NullPointerException
03-12 13:32:12.290: E/AndroidRuntime(614): at com.appname.fundeals.DealsAdapter.getChildrenCount(DealsAdapter.java:42)
03-12 13:32:12.290: E/AndroidRuntime(614): at android.widget.ExpandableListConnector.refreshExpGroupMetadataList(ExpandableListConnector.java:563)
03-12 13:32:12.290: E/AndroidRuntime(614): at android.widget.ExpandableListConnector.expandGroup(ExpandableListConnector.java:688)
03-12 13:32:12.290: E/AndroidRuntime(614): at android.widget.ExpandableListView.handleItemClick(ExpandableListView.java:562)
03-12 13:32:12.290: E/AndroidRuntime(614): at android.widget.ExpandableListView.performItemClick(ExpandableListView.java:522)
03-12 13:32:12.290: E/AndroidRuntime(614): at android.widget.AbsListView$PerformClick.run(AbsListView.java:2859)
03-12 13:32:12.290: E/AndroidRuntime(614): at android.widget.AbsListView$1.run(AbsListView.java:3533)
03-12 13:32:12.290: E/AndroidRuntime(614): at android.os.Handler.handleCallback(Handler.java:615)
03-12 13:32:12.290: E/AndroidRuntime(614): at android.os.Handler.dispatchMessage(Handler.java:92)
03-12 13:32:12.290: E/AndroidRuntime(614): at android.os.Looper.loop(Looper.java:137)
03-12 13:32:12.290: E/AndroidRuntime(614): at android.app.ActivityThread.main(ActivityThread.java:4745)
03-12 13:32:12.290: E/AndroidRuntime(614): at java.lang.reflect.Method.invokeNative(Native Method)
03-12 13:32:12.290: E/AndroidRuntime(614): at java.lang.reflect.Method.invoke(Method.java:511)
03-12 13:32:12.290: E/AndroidRuntime(614): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
03-12 13:32:12.290: E/AndroidRuntime(614): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
03-12 13:32:12.290: E/AndroidRuntime(614): at dalvik.system.NativeStart.main(Native Method)
的AndroidManifest.xml：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.appname.fundeals"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="21" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/Theme.AppCompat" >
<activity
android:name=".MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".inloggActivity" />
<activity android:name=".katagActivity" />
</application>
</manifest>
activity_main.xml中：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@drawable/bakgrund"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.appname.fundeals.MainActivity" >
<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="20dp"
android:text="Random Text"
android:textAppearance="?android:attr/textAppearanceLarge" />
<TextView
android:id="@+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_below="@+id/textView1"
android:layout_marginTop="75dp"
android:layout_marginLeft="10dp"
android:text="Username:"
android:textAppearance="?android:attr/textAppearanceMedium" />
/>
<EditText
android:id="@+id/usernameET"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBottom="@+id/textView2"
android:layout_marginLeft="35dp"
android:layout_toRightOf="@+id/textView2"
android:hint="Användarnamn" >
<requestFocus />
</EditText>
<TextView
android:id="@+id/textView3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/textView2"
android:layout_below="@+id/textView2"
android:layout_marginTop="40dp"
android:text="Password:"
android:textAppearance="?android:attr/textAppearanceMedium" />
<EditText
android:id="@+id/passwordET"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBottom="@+id/textView3"
android:layout_alignLeft="@+id/usernameET"
android:layout_alignRight="@+id/usernameET"
android:hint="lösenord"
android:inputType="textPassword" />
<TextView
android:id="@+id/attemptsLeftTV"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/textView3"
android:layout_below="@+id/textView3"
android:layout_marginLeft="30dp"
android:layout_marginTop="48dp"
android:text="Attempts Left:"
android:visibility="invisible"
android:textAppearance="?android:attr/textAppearanceMedium" />
<TextView
android:id="@+id/numberOfRemainingLoginAttemptsTV"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignRight="@+id/textView1"
android:layout_alignTop="@+id/attemptsLeftTV"
android:visibility="invisible" />
<TextView
android:id="@+id/loginLockedTV"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/loginBtn"
android:layout_marginTop="35dp"
android:layout_centerHorizontal="true"
android:textAppearance="?android:attr/textAppearanceMedium"
android:visibility="invisible" />
<Button
android:id="@+id/loginBtn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/numberOfRemainingLoginAttemptsTV"
android:layout_centerHorizontal="true"
android:onClick="authenticateLogin"
android:text="Login" />
<Button
android:id="@+id/FacebookBtn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/loginBtn"
android:layout_toLeftOf="@+id/usernameET"
android:onClick="authenticateLogin"
android:text="Facebook" />
MainActivity.java：
package com.appname.fundeals;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import com.appname.fundeals.R;
import android.annotation.SuppressLint;
import android.content.Intent;
import android.graphics.Color;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
@SuppressLint("NewApi")
public class MainActivity extends ActionBarActivity {
public class onClick implements OnClickListener {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
startActivity(new Intent(MainActivity.this, inloggActivity.class));
}
}
private EditText username;
private EditText password;
private Button login;
private TextView loginLockedTV;
private Button facebookBtn;
private TextView attemptsLeftTV;
private TextView numberOfRemainingLoginAttemptsTV;
int numberOfRemainingLoginAttempts = 3;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
facebookBtn = (Button) findViewById(R.id.FacebookBtn);
facebookBtn.setOnClickListener(new onClick());
setupVariables();
}
public void authenticateLogin(View view) {
if (username.getText().toString().equals("admin") &&
password.getText().toString().equals("admin")) {
Toast.makeText(getApplicationContext(), "Hello admin!",
Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(getApplicationContext(), "Seems like you 're not admin!",
Toast.LENGTH_SHORT).show();
numberOfRemainingLoginAttempts--;
attemptsLeftTV.setVisibility(View.VISIBLE);
numberOfRemainingLoginAttemptsTV.setVisibility(View.VISIBLE);
numberOfRemainingLoginAttemptsTV.setText(Integer.toString(numberOfRemainingLoginAttempts));
if (numberOfRemainingLoginAttempts == 0) {
login.setEnabled(false);
loginLockedTV.setVisibility(View.VISIBLE);
loginLockedTV.setBackgroundColor(Color.RED);
loginLockedTV.setText("LOGIN LOCKED!!!");
}
}
}
private void setupVariables() {
username = (EditText) findViewById(R.id.usernameET);
password = (EditText) findViewById(R.id.passwordET);
login = (Button) findViewById(R.id.loginBtn);
loginLockedTV = (TextView) findViewById(R.id.loginLockedTV);
attemptsLeftTV = (TextView) findViewById(R.id.attemptsLeftTV);
numberOfRemainingLoginAttemptsTV = (TextView) findViewById(R.id.numberOfRemainingLoginAttemptsTV);
numberOfRemainingLoginAttemptsTV.setText(Integer.toString(numberOfRemainingLoginAttempts));
}
}
activity_inlogg.xml：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@drawable/bakgrund" >
<TextView
android:id="@+id/textViewFirst"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginLeft="14dp"
android:layout_marginTop="20dp"
android:text="Random Text."
android:textStyle="bold" />
<ImageButton
android:id="@+id/imageButton1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/textViewFirst"
android:layout_centerHorizontal="true"
android:layout_marginTop="25dp"
android:background="#00000000"
android:src="@drawable/rkeepklar" />
<ImageButton
android:id="@+id/imageButton3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/imageButton2"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:layout_marginTop="6dp"
android:background="#00000000"
android:src="@drawable/stklarmarkerad" />
<ImageButton
android:id="@+id/imageButton2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/imageButton1"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:layout_marginTop="4dp"
android:background="#00000000"
android:src="@drawable/ndklar" />
</RelativeLayout>
inloggActivity.java（屏幕2）：
package com.appname.fundeals;
import com.appname.fundeals.inloggActivity.OnClick;
import com.appname.fundeals.R;
import android.app.Activity;
import android.graphics.Color;
import android.annotation.SuppressLint;
import android.content.Intent;
import android.widget.Toast;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class inloggActivity extends Activity {
public class OnClick implements OnClickListener {
@Override
public void onClick(View v) {
startActivity(new Intent(inloggActivity.this, katagActivity.class));
}
}
private Button imageButton1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_inlogg);
Button imageButton1 = (Button) findViewById(R.id.imageButton1);
imageButton1.setOnClickListener(new OnClick());
}
}
activity_katag.xml（SCREEN3）：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="match_parent"
android:background="@drawable/bakgrund"
android:paddingLeft="16dp"
android:paddingRight="16dp"
android:paddingTop="16dp"
android:paddingBottom="16dp"
>
<ExpandableListView
android:id="@+id/exp_list"
android:layout_height="match_parent"
android:layout_width="match_parent"
android:indicatorLeft="?android:attr/expandableListPreferredItemIndicatorLeft"
android:divider="#A4C739"
android:dividerHeight="0.5dp"
></ExpandableListView>
</RelativeLayout>
katagActivity.java：
package com.appname.fundeals;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.widget.ExpandableListView;
public class katagActivity extends Activity {
private static final HashMap<String, List<String>> Deals_Catagory = null;
HashMap<String, List<String>> Deals_category;
List<String> Deals_list;
ExpandableListView Exp_list;
DealsAdapter adapter;
@Override
protected void onCreate (Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_katag);
Exp_list = (ExpandableListView) findViewById(R.id.exp_list);
Deals_category = DataProvider.getInfo();
Deals_list = new ArrayList<String>(Deals_category.keySet());
adapter = new DealsAdapter(this, Deals_Catagory, Deals_list);
Exp_list.setAdapter(adapter);
}
}
DealsAdapter.java：
package com.appname.fundeals;
import java.util.HashMap;
import java.util.List;
import com.appname.fundeals.R;
import android.content.Context;
import android.graphics.Typeface;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseExpandableListAdapter;
import android.widget.TextView;
public class DealsAdapter extends BaseExpandableListAdapter {
private Context ctx;
private HashMap<String, List<String>> Deals_Catagory;
private List<String> Deals_List;
public DealsAdapter(Context ctx, HashMap<String, List<String>> Deals_Catagory, List<String> Deals_List) {
this.ctx = ctx;
this.Deals_Catagory = Deals_Catagory;
this.Deals_List = Deals_List;
// TODO Auto-generated constructor stub
}
@Override
public int getGroupCount() {
return Deals_List.size();
}
@Override
public int getChildrenCount(int arg0) {
return Deals_Catagory.get(Deals_List.get(arg0)).size();
}
@Override
public Object getGroup(int arg0) {
return Deals_List.get(arg0);
}
@Override
public Object getChild(int parent, int child) {
// TODO Auto-generated method stub
return Deals_Catagory.get(Deals_List.get(parent)).get(child);
}
@Override
public long getGroupId(int arg0) {
// TODO Auto-generated method stub
return arg0;
}
@Override
public long getChildId(int parent, int child) {
// TODO Auto-generated method stub
return child;
}
@Override
public boolean hasStableIds() {
// TODO Auto-generated method stub
return false;
}
@Override
public View getGroupView(int parent, boolean isExpanded, View convertView, ViewGroup parentView) {
// TODO Auto-generated method stub
String group_title = (String) getGroup(parent);
if(convertView == null)
{
LayoutInflater inflator = (LayoutInflater) ctx.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = inflator.inflate(R.layout.parent_deal1, parentView, false);
}
TextView parent_textView = (TextView) convertView.findViewById(R.id.parent_deal1);
parent_textView.setTypeface(null, Typeface.BOLD);
parent_textView.setText(group_title);
return convertView;
}
@Override
public View getChildView(int parent, int child, boolean lastChild, View convertView,
ViewGroup parentview) {
String child_title = (String) getChild(parent, child);
if (convertView == null)
{
LayoutInflater inflator = (LayoutInflater) ctx.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = inflator.inflate(R.layout.child_deal1, parentview, false);
}
// TODO Auto-generated method stub
TextView child_textView = (TextView) convertView.findViewById(R.id.child_deal1);
child_textView.setText(child_title);
return convertView;
}
@Override
public boolean isChildSelectable(int groupPosition, int childPosition) {
// TODO Auto-generated method stub
return false;
}
}
DataProvider.java：
package com.appname.fundeals;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
public class DataProvider {
public static HashMap<String, List<String>> getInfo()
{
HashMap<String, List<String>> DealsDetails = new HashMap<String, List<String>>();
List<String> Deal_1 = new ArrayList<String>();
Deal_1.add("Text");
List<String> Deal_2 = new ArrayList<String>();
Deal_2.add("Text");
List<String> Deal_3 = new ArrayList<String>();
Deal_3.add("Text");
List<String> Deal_4 = new ArrayList<String>();
Deal_4.add("Text");
DealsDetails.put("Deal 1", Deal_1);
DealsDetails.put("Deal 2", Deal_2);
DealsDetails.put("Deal 3", Deal_3);
DealsDetails.put("Deal 4", Deal_4);
return DealsDetails;
}
}