我有两个活动和一个数据库。这是第一个：
public class FeelingsMain extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initList();
ListView lv = (ListView)findViewById(R.id.pageLayout);
//design the listview with the adapter
SimpleAdapter simpleAdpt = new SimpleAdapter(this, feelingsList, android.R.layout.simple_list_item_1, new String[] {"feeling"},new int[] {android.R.id.text1});
lv.setAdapter(simpleAdpt);
lv.setOnItemClickListener(viewNeeds);
}
List<Map<String, String>> feelingsList = new ArrayList<Map<String,String>>();
private void initList(){
//populate the feelingsList
feelingsList.add(createFeeling("feeling","wonderful"));
feelingsList.add(createFeeling("feeling","content"));
feelingsList.add(createFeeling("feeling","joyful"));
feelingsList.add(createFeeling("feeling","tired"));
feelingsList.add(createFeeling("feeling","gay"));
feelingsList.add(createFeeling("feeling","sad"));
feelingsList.add(createFeeling("feeling","amazing"));
}
private HashMap<String, String>createFeeling(String key,String name){
HashMap<String, String>feeling = new HashMap<String,String>();
feeling.put(key, name);
return feeling;
}
OnItemClickListener viewNeeds = new OnItemClickListener(){
@Override
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,
long arg3) {
// TODO Auto-generated method stub
//create variable for database input
String feeling = feelingsList.get(arg2).toString();
Bundle basket = new Bundle();
basket.putString("aFeeling", feeling);
Intent gotoNeeds=
new Intent(FeelingsMain.this, Needs.class);
startActivity(gotoNeeds);
}
};
}
哪个应该开始这个活动...
public class Needs extends Activity {
String gotTheFeeling;
private DatabaseConnectToActivities database;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Receive string from feelingsmain
Bundle gotFeeling = getIntent().getExtras();
gotTheFeeling = gotFeeling.getString("aFeeling");
// new database object
database = new DatabaseConnectToActivities(this);
database.open();
initList();
ListView lv = (ListView) findViewById(R.id.pageLayout);
SimpleAdapter simpleAdpt = new SimpleAdapter(this, needsList,
android.R.layout.simple_list_item_1, new String[] { "need" },
new int[] { android.R.id.text1 });
lv.setAdapter(simpleAdpt);
lv.setOnItemClickListener(backToFeelings);
}
List<Map<String, String>> needsList = new ArrayList<Map<String, String>>();
protected String feelingForDb;
public void initList() {
needsList.add(createNeed("need", "space"));
needsList.add(createNeed("need", "peace"));
needsList.add(createNeed("need", "calm"));
needsList.add(createNeed("need", "understanding"));
needsList.add(createNeed("need", "to be heard"));
needsList.add(createNeed("need", "to be seen"));
needsList.add(createNeed("need", "love"));
}
private HashMap<String, String> createNeed(String key, String name) {
HashMap<String, String> need = new HashMap<String, String>();
need.put(key, name);
return need;
}
OnItemClickListener backToFeelings = new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,
long arg3) {
String need = needsList.get(arg2).toString();
database.insertEmotions(gotTheFeeling, need);
database.close();
Intent toFeelings = new Intent(Needs.this, FeelingsMain.class);
startActivity(toFeelings);
}
};
}
但是当我点击listview项目时，我收到一个NullPointerException。 这是logcat：
07-22 21:01:54.174: E/AndroidRuntime(9687): FATAL EXCEPTION: main
07-22 21:01:54.174: E/AndroidRuntime(9687): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.feeling/com.example.feeling.Needs}: java.lang.NullPointerException
07-22 21:01:54.174: E/AndroidRuntime(9687): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
07-22 21:01:54.174: E/AndroidRuntime(9687): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
07-22 21:01:54.174: E/AndroidRuntime(9687): at android.app.ActivityThread.access$600(ActivityThread.java:141)
07-22 21:01:54.174: E/AndroidRuntime(9687): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
07-22 21:01:54.174: E/AndroidRuntime(9687): at android.os.Handler.dispatchMessage(Handler.java:99)
07-22 21:01:54.174: E/AndroidRuntime(9687): at android.os.Looper.loop(Looper.java:137)
07-22 21:01:54.174: E/AndroidRuntime(9687): at android.app.ActivityThread.main(ActivityThread.java:5041)
07-22 21:01:54.174: E/AndroidRuntime(9687): at java.lang.reflect.Method.invokeNative(Native Method)
07-22 21:01:54.174: E/AndroidRuntime(9687): at java.lang.reflect.Method.invoke(Method.java:511)
07-22 21:01:54.174: E/AndroidRuntime(9687): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
07-22 21:01:54.174: E/AndroidRuntime(9687): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
07-22 21:01:54.174: E/AndroidRuntime(9687): at dalvik.system.NativeStart.main(Native Method)
07-22 21:01:54.174: E/AndroidRuntime(9687): Caused by: java.lang.NullPointerException
07-22 21:01:54.174: E/AndroidRuntime(9687): at com.example.feeling.Needs.onCreate(Needs.java:31)
07-22 21:01:54.174: E/AndroidRuntime(9687): at android.app.Activity.performCreate(Activity.java:5104)
07-22 21:01:54.174: E/AndroidRuntime(9687): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
07-22 21:01:54.174: E/AndroidRuntime(9687): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
07-22 21:01:54.174: E/AndroidRuntime(9687): ... 11 more
07-22 21:01:55.531: D/dalvikvm(9687): GC_CONCURRENT freed 129K, 10% free 2648K/2916K, paused 107ms+57ms, total 1409ms
07-22 21:06:55.315: I/Process(9687): Sending signal. PID: 9687 SIG: 9
这是我的清单文件：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.feeling"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="17" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.example.feeling.FeelingsMain"
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="com.example.feeling.Needs"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name="com.example.feeling.DatabaseHelp"
android:label="@string/app_name" >
</activity>
<activity
android:name="com.example.feeling.DatabaseConnectToActivities"
android:label="@string/app_name" >
</activity>
</application>
</manifest>
您能否帮助确定此异常的原因？
答案 0 :(得分：1)
你没有在你的意图中添加任何额外内容。
Bundle gotFeeling = getIntent().getExtras();
gotTheFeeling = gotFeeling.getString("aFeeling");
但你试图得到一个。
String feeling = feelingsList.get(arg2).toString();
Bundle basket = new Bundle();
basket.putString("aFeeling", feeling);
Intent gotoNeeds=
new Intent(FeelingsMain.this, Needs.class);
startActivity(gotoNeeds);
我相信你已经把你的篮子套装与你尝试发送的额外内容混淆了。
试试这个。
String feeling = feelingsList.get(arg2).toString();
Intent gotoNeeds=
new Intent(FeelingsMain.this, Needs.class);
gotoNeeds.putExtra("aFeeling", feeling);
startActivity(gotoNeeds);
答案 1 :(得分：0)
尝试
gotoNeeds.putExtra("aFeeling", feeling);
而不是创建新的Bundle。