在两个类之间切换，但程序已停止。为什么？
在两个类之间切换，但程序已停止。为什么？
提问于 2012-11-11 14:33:40
我在程序中有两节课。我想当用户点击两个第一个按钮，程序转到第一类(主类)。我不使用片段。我写了这段代码，但当运行该程序并单击Places按钮时，该程序已停止。为什么？(在我添加按钮点击之前，程序会正确运行)。LogCat写入null异常，但我找不到何处为null?！请帮帮我。
Location.java
public class Location extends MapActivity {
private FrameLayout linear;
private MapView map;
private MapController controller;
private EditText text_location;
GeoPoint searchLocation;
GeoPoint mylocation;
double myLatitude=0;
double myLongitude=0;
List<Overlay> mapOverlays;
Drawable drawable;
SimpleItemizedOverlay itemizedOverlay;
//Other classes
private Button mHome;
private Button mProduct;
private Button mPlaces;
private WebView mWebView;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.location);
initOtherButtons();
//....
}
private void initOtherButtons(){
mHome=(Button)findViewById(R.id.button_home);
mProduct=(Button)findViewById(R.id.button_product);
mPlaces=(Button)findViewById(R.id.button_places);
mWebView=(WebView)findViewById(R.id.web_view);
//TEST
mHome.setOnClickListener(onClickListener);
mProduct.setOnClickListener(onClickListener);
}
private OnClickListener onClickListener=new OnClickListener(){
Intent i=new Intent(Location.this,Main.class);
public void onClick(View v){
switch(v.getId()){
case R.id.button_home:
startActivity(i);
break;
case R.id.button_product:
startActivity(i);
break;
}
}
};
}Main.java
public class Main extends Activity {
private WebView mWebView;
private Button mHome;
private Button mProduct;
private Button mPlaces;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mWebView = (WebView)findViewById(R.id.web_view);
mWebView.loadUrl("http://www.google.com");
mHome = (Button)findViewById(R.id.button_home);
mProduct=(Button)findViewById(R.id.button_product);
mPlaces=(Button)findViewById(R.id.button_places);
mHome.setOnClickListener(onClickListener);
mProduct.setOnClickListener(onClickListener);
mPlaces.setOnClickListener(onClickListener);
}
private OnClickListener onClickListener=new OnClickListener(){
public void onClick(View v){
switch(v.getId()){
case R.id.button_home:
mWebView.loadUrl("http://www.google.com");
break;
case R.id.button_product:
mWebView.loadUrl("http://www.google.com");
break;
case R.id.button_places:
Intent i=new Intent(Main.this,Location.class);
startActivity(i);
break;
}
}
};
}Manifest.xml：
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="org.example.loyaltier"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="9"
android:targetSdkVersion="15" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
<application
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<uses-library android:name="com.google.android.maps" />
<activity
android:name=".Main"
android:label="@string/title_activity_main" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".Location"
android:label="@string/Location_title">
</activity>
<activity android:name=".SimpleItemizedOverlay"
android:label="@string/app_name">
</activity>
<activity android:name=".BalloonOverlayView"
android:label="@string/app_name">
</activity>
<activity android:name=".BalloonItemizedOverlay"
android:label="@string/app_name">
</activity>
</application>
</manifest>LogCat：
11-11 09:56:16.506: D/OpenGLRenderer(18214): Flushing caches (mode 1)
11-11 09:56:16.506: D/OpenGLRenderer(18214): Flushing caches (mode 0)
11-11 09:56:38.006: D/dalvikvm(18275): GC_CONCURRENT freed 172K, 2% free 14351K/14599K, paused 9ms+2ms
11-11 09:56:38.053: D/dalvikvm(18275): GC_FOR_ALLOC freed 7K, 2% free 14715K/14983K, paused 11ms
11-11 09:56:39.287: D/AndroidRuntime(18275): Shutting down VM
11-11 09:56:39.287: W/dalvikvm(18275): threadid=1: thread exiting with uncaught exception (group=0x40a891f8)
11-11 09:56:39.295: E/AndroidRuntime(18275): FATAL EXCEPTION: main
11-11 09:56:39.295: E/AndroidRuntime(18275): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{org.example.loyaltier/org.example.loyaltier.Location}: java.lang.NullPointerException
11-11 09:56:39.295: E/AndroidRuntime(18275): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1879)
11-11 09:56:39.295: E/AndroidRuntime(18275): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1980)
11-11 09:56:39.295: E/AndroidRuntime(18275): at android.app.ActivityThread.access$600(ActivityThread.java:122)
11-11 09:56:39.295: E/AndroidRuntime(18275): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1146)
11-11 09:56:39.295: E/AndroidRuntime(18275): at android.os.Handler.dispatchMessage(Handler.java:99)
11-11 09:56:39.295: E/AndroidRuntime(18275): at android.os.Looper.loop(Looper.java:137)
11-11 09:56:39.295: E/AndroidRuntime(18275): at android.app.ActivityThread.main(ActivityThread.java:4340)
11-11 09:56:39.295: E/AndroidRuntime(18275): at java.lang.reflect.Method.invokeNative(Native Method)
11-11 09:56:39.295: E/AndroidRuntime(18275): at java.lang.reflect.Method.invoke(Method.java:511)
11-11 09:56:39.295: E/AndroidRuntime(18275): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
11-11 09:56:39.295: E/AndroidRuntime(18275): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
11-11 09:56:39.295: E/AndroidRuntime(18275): at dalvik.system.NativeStart.main(Native Method)
11-11 09:56:39.295: E/AndroidRuntime(18275): Caused by: java.lang.NullPointerException
11-11 09:56:39.295: E/AndroidRuntime(18275): at android.content.ContextWrapper.getPackageName(ContextWrapper.java:127)
11-11 09:56:39.295: E/AndroidRuntime(18275): at android.content.ComponentName.<init>(ComponentName.java:75)
11-11 09:56:39.295: E/AndroidRuntime(18275): at android.content.Intent.<init>(In tent.java:3004)
11-11 09:56:39.295: E/AndroidRuntime(18275): at org.example.loyaltier.Location$1.<init>(Location.java:118)
11-11 09:56:39.295: E/AndroidRuntime(18275): at org.example.loyaltier.Location.<init>(Location.java:117)
11-11 09:56:39.295: E/AndroidRuntime(18275): at java.lang.Class.newInstanceImpl(Native Method)
11-11 09:56:39.295: E/AndroidRuntime(18275): at java.lang.Class.newInstance(Class.java:1319)
11-11 09:56:39.295: E/AndroidRuntime(18275): at android.app.Instrumentation.newActivity(Instrumentation.java:1023)
11-11 09:56:39.295: E/AndroidRuntime(18275): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1870)
11-11 09:56:39.295: E/AndroidRuntime(18275): ... 11 more编辑:简单程序
private OnClickListener onClickListener=new OnClickListener(){
public void onClick(View v){
switch(v.getId()){
case R.id.button_home:
mWebView.loadUrl("http://www.google.com");
break;
}
}
};回答 4
Stack Overflow用户
发布于 2012-11-11 14:39:31
可能是manifest.xml中的activity声明不正确(或者根本没有)。验证清单并确保活动已声明且名称正确。
Stack Overflow用户
发布于 2012-11-11 14:40:13
它看起来像是一个NullPointerException：
11-11 09:56:39.295: E/AndroidRuntime(18275): Caused by: java.lang.NullPointerException你的两个活动类都在清单中吗？如果是这样，请检查Main的onCreate中是否有NPE，或者在此处发布您的代码。
Stack Overflow用户
发布于 2012-11-11 14:57:23
如果您是在模拟器中运行此程序，那么请检查您的模拟器是否支持MapView所需的Google API。请查看此链接以了解AVD设置。
EDIT01:请尝试将Intent i=new Intent(Location.this,Main.class);移入onClick()方法，如下所示：
private OnClickListener onClickListener=new OnClickListener(){
public void onClick(View v){
Intent i=new Intent(Location.this,Main.class);
switch(v.getId()){
case R.id.button_home:
startActivity(i);
break;
case R.id.button_product:
startActivity(i);
break;
}
}
};页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/13329115
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