如何在Android应用程序中调试NullPointerException？ [英] How to debug a NullPointerException in an Android app?
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问题描述
我有一个非常简单的应用程序不能正确启动。应用程序应该加载一个闪屏，然后加载主应用程序。由于某种原因现在不起作用 -
I have a very simple app which isn't starting correctly. The app should load a splashscreen, and then the main app. For some reason it's now not working -
Logcat：
02-08 13:30:41.846: E/AndroidRuntime(275): Uncaught handler: thread main exiting due to uncaught exception
02-08 13:30:41.865: E/AndroidRuntime(275): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.KES.GApps/com.KES.GApps.Splashscreen}: java.lang.NullPointerException
02-08 13:30:41.865: E/AndroidRuntime(275): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2496)
02-08 13:30:41.865: E/AndroidRuntime(275): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512)
02-08 13:30:41.865: E/AndroidRuntime(275): at android.app.ActivityThread.access$2200(ActivityThread.java:119)
02-08 13:30:41.865: E/AndroidRuntime(275): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863)
02-08 13:30:41.865: E/AndroidRuntime(275): at android.os.Handler.dispatchMessage(Handler.java:99)
02-08 13:30:41.865: E/AndroidRuntime(275): at android.os.Looper.loop(Looper.java:123)
02-08 13:30:41.865: E/AndroidRuntime(275): at android.app.ActivityThread.main(ActivityThread.java:4363)
02-08 13:30:41.865: E/AndroidRuntime(275): at java.lang.reflect.Method.invokeNative(Native Method)
02-08 13:30:41.865: E/AndroidRuntime(275): at java.lang.reflect.Method.invoke(Method.java:521)
02-08 13:30:41.865: E/AndroidRuntime(275): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
02-08 13:30:41.865: E/AndroidRuntime(275): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
02-08 13:30:41.865: E/AndroidRuntime(275): at dalvik.system.NativeStart.main(Native Method)
02-08 13:30:41.865: E/AndroidRuntime(275): Caused by: java.lang.NullPointerException
02-08 13:30:41.865: E/AndroidRuntime(275): at android.view.ViewGroup.addViewInner(ViewGroup.java:1860)
02-08 13:30:41.865: E/AndroidRuntime(275): at android.view.ViewGroup.addView(ViewGroup.java:1756)
02-08 13:30:41.865: E/AndroidRuntime(275): at android.view.ViewGroup.addView(ViewGroup.java:1736)
02-08 13:30:41.865: E/AndroidRuntime(275): at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:217)
02-08 13:30:41.865: E/AndroidRuntime(275): at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:207)
02-08 13:30:41.865: E/AndroidRuntime(275): at android.app.Activity.setContentView(Activity.java:1633)
02-08 13:30:41.865: E/AndroidRuntime(275): at com.KES.GApps.Splashscreen.onCreate(Splashscreen.java:13)
02-08 13:30:41.865: E/AndroidRuntime(275): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
02-08 13:30:41.865: E/AndroidRuntime(275): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2459)
02-08 13:30:41.865: E/AndroidRuntime(275): ... 11 more
02-08 13:30:41.884: I/dalvikvm(275): threadid=7: reacting to signal 3
02-08 13:30:41.884: E/dalvikvm(275): Unable to open stack trace file '/data/anr/traces.txt': Permission denied
xml为splashscreen（welcome.xml）：
xml for the splashscreen (welcome.xml):
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="@drawable/img1"
android:orientation="vertical" >
<ImageView
android:id="@+id/imageView1"
android:layout_width="wrap_content"
android:layout_height="200dp"
android:layout_gravity="fill_horizontal"
android:contentDescription="@string/crestinfo"
android:src="@drawable/logov2" />
<TextView
android:id="@+id/welcomescreen"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="right"
android:text="@string/welcomescreen"
android:textAppearance="?android:attr/textAppearanceLarge"
android:textColor="#ffffff"
android:textStyle="bold" android:padding="5dp" android:textSize="15pt" />
</LinearLayout>
java：
package com.KES.GApps;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
public class Splashscreen extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.welcome);
Thread splashThread = new Thread() {
@Override
public void run() {
try {
int waited = 0;
while (waited < 2000) {
sleep(100);
waited += 100;
}
} catch (InterruptedException e) {
// do nothing
} finally {
finish();
Intent i = new Intent();
i.setClassName("com.KES.GApps",
"com.KES.GApps.KingEdwardVIISchoolActivity");
startActivity(i);
}
}
};
splashThread.start();
}
}
清单文件：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.KES.GApps"
android:versionCode="6"
android:versionName="1.5" >
<uses-sdk android:minSdkVersion="7" />
<uses-permission android:name="android.permission.INTERNET" />
<application
android:name="KingEdwardVIISchool"
android:debuggable="true"
android:icon="@drawable/icon"
android:label="@string/app_name"
android:launchMode="standard" >
<activity
android:name="KingEdwardVIISchoolActivity"
android:configChanges="orientation|keyboardHidden"
android:label="@string/app_name"
android:screenOrientation="portrait" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
</intent-filter>
</activity>
<activity
android:name="Splashscreen"
android:configChanges="orientation|keyboardHidden"
android:label="@string/app_name"
android:screenOrientation="portrait" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
推荐答案
我也遇到这个问题一次。那么我做的是我刚从我的 R.java 复制了布局的 id ，并将其直接粘贴到的setContentView（）。即，在这种情况下，在 R.java - > 布局中的，它的工作正常。 id / code>。那么我的应用程序成功运行，无一例外所以我意识到这只是一个暂时的问题。重新启动我的eclipse（有时你必须完全重新启动系统）我再次替换了＃code> R.layout.welcome
希望这有帮助...
I was also suffering from this problem once. Then what i did was i just copied the id of the layout from my R.java and pasted it directly to setContentView(). ie, Here in your case the id of welcome in R.java->layout. then my app ran successfully without any exception. Thus i realized that its just a temporary problem. After restarting my eclipse (sometimes you have to restart your system fully) I replaced the id again by R.layout.welcome and it worked fine.
Hope this helps...
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