我正在开发一个代码，用于在启动画面后运行视图寻呼机。
我编写了连接2个活动的代码，但是当我运行程序时，我一直收到nullPointerException。
第一项活动：
package lk.sidadiya.sidadiya;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
public class SplashScreen extends Activity {
// Splash screen timer
private static int SPLASH_TIME_OUT = 3000;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_splash);
new Handler().postDelayed(new Runnable() {
/*
* Showing splash screen with a timer. This will be useful when you
* want to show case your app logo / company
*/
@Override
public void run() {
// This method will be executed once the timer is over
// Start your app main activity
Intent i = new Intent(SplashScreen.this, WelcomeScreen.class);
startActivity(i);
// close this activity
finish();
}
}, SPLASH_TIME_OUT);
}
}
第二项活动：
package lk.sidadiya.sidadiya;
import lk.sidadiya.tabswipe.adapter.TabsPagerAdapter;
import lk.sidadiya.sidadiya.R;
import android.app.ActionBar;
import android.app.ActionBar.Tab;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;
public class WelcomeScreen extends FragmentActivity implements
ActionBar.TabListener {
private ViewPager viewPager;
private TabsPagerAdapter mAdapter;
private ActionBar actionBar;
// Tab titles
private String[] tabs = { "Top Rated", "Games", "Movies" };
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_screen);
// Initilization
viewPager = (ViewPager) findViewById(R.id.pager);
actionBar = getActionBar();
mAdapter = new TabsPagerAdapter(getSupportFragmentManager());
viewPager.setAdapter(mAdapter);
actionBar.setHomeButtonEnabled(false);
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
// Adding Tabs
for (String tab_name : tabs) {
actionBar.addTab(actionBar.newTab().setText(tab_name)
.setTabListener(this));
}
/**
* on swiping the viewpager make respective tab selected
* */
viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
@Override
public void onPageSelected(int position) {
// on changing the page
// make respected tab selected
actionBar.setSelectedNavigationItem(position);
}
@Override
public void onPageScrolled(int arg0, float arg1, int arg2) {
}
@Override
public void onPageScrollStateChanged(int arg0) {
}
});
}
@Override
public void onTabReselected(Tab tab, FragmentTransaction ft) {
}
@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
// on tab selected
// show respected fragment view
viewPager.setCurrentItem(tab.getPosition());
}
@Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
}
}
清单：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="lk.sidadiya.sidadiya"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="14"
android:targetSdkVersion="19" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<!-- Splash screen -->
<activity
android:name="lk.sidadiya.sidadiya.SplashScreen"
android:label="@string/app_name"
android:screenOrientation="portrait"
android:theme="@android:style/Theme.Black.NoTitleBar" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name="lk.sidadiya.sidadiya.WelcomeScreen"
android:label="@string/app_name"
android:screenOrientation="portrait"
android:theme="@android:style/Theme.Black.NoTitleBar" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<!-- Main activity -->
<activity
android:name="lk.sidadiya.sidadiya.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>
</application>
</manifest>
Log cat：
04-09 15:30:40.405: D/dalvikvm(14241): GC_FOR_ALLOC freed 53K, 5% free 8068K/8451K, paused 41ms, total 41ms
04-09 15:30:40.435: D/scheduleTraversals(14241): mTraversalScheduled:false
04-09 15:30:40.445: D/dalvikvm(14241): GC_CONCURRENT freed 4K, 5% free 8522K/8903K, paused 2ms+7ms, total 35ms
04-09 15:30:40.445: D/scheduleTraversals(14241): mTraversalScheduled:true
04-09 15:30:40.445: D/performTraversals(14241): mAdded:true
04-09 15:30:40.455: D/ViewRootImpl(14241): relayoutWindow()-viewVisibility: 0
04-09 15:30:40.495: I/Adreno200-EGL(14241): <qeglDrvAPI_eglInitialize:294>: EGL 1.4 QUALCOMM build: AU_LINUX_ANDROID_JB_REL_RB3.04.01.01.13.044_msm8960_JB_REL_RB3.1_CL3449569_release_AU (CL3449569)
04-09 15:30:40.495: I/Adreno200-EGL(14241): Build Date: 05/13/13 Mon
04-09 15:30:40.495: I/Adreno200-EGL(14241): Local Branch:
04-09 15:30:40.495: I/Adreno200-EGL(14241): Remote Branch: m/jb_rel_rb3.1
04-09 15:30:40.495: I/Adreno200-EGL(14241): Local Patches: NONE
04-09 15:30:40.495: I/Adreno200-EGL(14241): Reconstruct Branch: AU_LINUX_ANDROID_JB_REL_RB3.04.01.01.13.044 + df3bc97 + NOTHING
04-09 15:30:40.555: D/scheduleTraversals(14241): mTraversalScheduled:false
04-09 15:30:40.555: D/scheduleTraversals(14241): mTraversalScheduled:true
04-09 15:30:40.566: D/scheduleTraversals(14241): mTraversalScheduled:true
04-09 15:30:40.566: D/performTraversals(14241): mAdded:true
04-09 15:30:43.489: W/dalvikvm(14241): threadid=1: thread exiting with uncaught exception (group=0x40c81450)
04-09 15:30:43.489: E/AndroidRuntime(14241): FATAL EXCEPTION: main
04-09 15:30:43.489: E/AndroidRuntime(14241): java.lang.RuntimeException: Unable to start activity ComponentInfo{lk.sidadiya.sidadiya/lk.sidadiya.sidadiya.WelcomeScreen}: java.lang.NullPointerException
04-09 15:30:43.489: E/AndroidRuntime(14241): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2065)
04-09 15:30:43.489: E/AndroidRuntime(14241): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2090)
04-09 15:30:43.489: E/AndroidRuntime(14241): at android.app.ActivityThread.access$600(ActivityThread.java:136)
04-09 15:30:43.489: E/AndroidRuntime(14241): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1201)
04-09 15:30:43.489: E/AndroidRuntime(14241): at android.os.Handler.dispatchMessage(Handler.java:99)
04-09 15:30:43.489: E/AndroidRuntime(14241): at android.os.Looper.loop(Looper.java:137)
04-09 15:30:43.489: E/AndroidRuntime(14241): at android.app.ActivityThread.main(ActivityThread.java:4800)
04-09 15:30:43.489: E/AndroidRuntime(14241): at java.lang.reflect.Method.invokeNative(Native Method)
04-09 15:30:43.489: E/AndroidRuntime(14241): at java.lang.reflect.Method.invoke(Method.java:511)
04-09 15:30:43.489: E/AndroidRuntime(14241): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:798)
04-09 15:30:43.489: E/AndroidRuntime(14241): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:565)
04-09 15:30:43.489: E/AndroidRuntime(14241): at dalvik.system.NativeStart.main(Native Method)
04-09 15:30:43.489: E/AndroidRuntime(14241): Caused by: java.lang.NullPointerException
04-09 15:30:43.489: E/AndroidRuntime(14241): at lk.sidadiya.sidadiya.WelcomeScreen.onCreate(WelcomeScreen.java:33)
04-09 15:30:43.489: E/AndroidRuntime(14241): at android.app.Activity.performCreate(Activity.java:5008)
04-09 15:30:43.489: E/AndroidRuntime(14241): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
04-09 15:30:43.489: E/AndroidRuntime(14241): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2029)
04-09 15:30:43.489: E/AndroidRuntime(14241): ... 11 more
答案 0 :(得分：3)
您的Manifest.xml文件中存在问题。您已将两个活动定义为Launcher。使用以下代码更改Manifest.xml，然后重试
<activity
android:name="lk.sidadiya.sidadiya.SplashScreen"
android:label="@string/app_name"
android:screenOrientation="portrait"
android:theme="@android:style/Theme.Black.NoTitleBar" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name="lk.sidadiya.sidadiya.WelcomeScreen"
android:label="@string/app_name"
android:screenOrientation="portrait">
</activity>
答案 1 :(得分：0)
您必须指定哪个是您的默认启动器活动。因此您必须更改清单文件
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="lk.sidadiya.sidadiya"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="14"
android:targetSdkVersion="19" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<!-- Splash screen -->
<activity
android:name="lk.sidadiya.sidadiya.SplashScreen"
android:label="@string/app_name"
android:screenOrientation="portrait"
android:theme="@android:style/Theme.Black.NoTitleBar" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.DEFAULT"
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name="lk.sidadiya.sidadiya.WelcomeScreen"
android:label="@string/app_name"
android:screenOrientation="portrait"
android:theme="@android:style/Theme.Black.NoTitleBar" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<!-- Main activity -->
<activity
android:name="lk.sidadiya.sidadiya.MainActivity"
android:label="@string/app_name" >
</activity>
</application>
</manifest>