《Android应用开发攻略》——3.6 应用程序崩溃排错

3.6 应用程序崩溃排错

Ulysses Levy3.6.1 问题应用崩溃，而原因不确定（参见图3-14）。

3.6.2 解决方案 从查看日志开始。 3.6.3 讨论 遇到应用程序崩溃时，我们可以使用adb logcat命令或者Eclipse LogCat窗口查看AVD的日志。例3-3说明了如何用adb logcat查看堆栈跟踪，找到故障的位置。 例3-3：“权限拒绝”问题的堆栈跟踪 E/DatabaseUtils( 53): Writing exception to parcel E/DatabaseUtils( 53): java.lang.SecurityException: Permission Denial: writing com.android.providers.settings.SettingsProvider uri content://settings/system from pid=430, uid=10030 requires android.permission.WRITE_SETTINGS E/DatabaseUtils( 53): at android.content.ContentProvider$Transport. enforceWritePermission(ContentProvider.java:294) E/DatabaseUtils( 53): at android.content.ContentProvider$Transport. insert(ContentProvider.java:149) E/DatabaseUtils( 53): at android.content.ContentProviderNative. onTransact(ContentProviderNative.java:140) E/DatabaseUtils( 53): at android.os.Binder.execTransact(Binder.java:287) E/DatabaseUtils( 53): at com.android.server.SystemServer.init1(Native Method) E/DatabaseUtils( 53): at com.android.server.SystemServer.main(SystemServer.java:497) E/DatabaseUtils( 53): at java.lang.reflect.Method.invokeNative(Native Method) E/DatabaseUtils( 53): at java.lang.reflect.Method.invoke(Method.java:521) E/DatabaseUtils( 53): at com.android.internal.os. ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860) E/DatabaseUtils( 53): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) E/DatabaseUtils( 53): at dalvik.system.NativeStart.main(Native Method) D/AndroidRuntime( 430): Shutting down VM W/dalvikvm( 430): threadid=3: thread exiting with uncaught exception (group=0x4001b188) ... 在例3-3中，我们遇到了权限问题。这一特殊实例的解决方案是在AndroidManifest.xml文件中添加WRITE_SETTINGS权限。 <manifest ... > <application ... /> <uses-permission android:name="android.permission.WRITE_SETTINGS" /> </manifest>

另一种相当常见的错误是空指针异常（NPE）。例3-4显示了LogCat输出。例3-4：LogCat输出

I/ActivityManager( 53): Displayed activity com.android.launcher/.Launcher: 28640 ms (total 28640 ms) I/ActivityManager( 53): Starting activity: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10200000 cmp=com.aschyiel.disp/.Disp } I/ActivityManager( 53): Start proc com.aschyiel.disp for activity com.aschyiel.disp/.Disp: pid=214 uid=10030 gids={1015} I/ARMAssembler( 53): generated scanline__00000177:03515104_00000001_00000000 [ 73 ipp] (95 ins) at [0x47c588:0x47c704] in 2087627 ns I/ARMAssembler( 53): generated scanline__00000077:03545404_00000004_00000000 [ 47 ipp] (67 ins) at [0x47c708:0x47c814] in 1834173 ns I/ARMAssembler( 53): generated scanline__00000077:03010104_00000004_00000000 [ 22 ipp] (41 ins) at [0x47c818:0x47c8bc] in 653016 ns D/AndroidRuntime( 214): Shutting down VM W/dalvikvm( 214): threadid=3: thread exiting with uncaught exception (group=0x4001b188) E/AndroidRuntime( 214): Uncaught handler: thread main exiting due to uncaught exception E/AndroidRuntime( 214): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.aschyiel.disp/com.aschyiel.disp.Disp}:java.lang.NullPointerException E/AndroidRuntime( 214): at android.app.ActivityThread.performLaunchActivity( ActivityThread.java:2496) E/AndroidRuntime( 214): at android.app.ActivityThread.handleLaunchActivity( ActivityThread.java:2512) E/AndroidRuntime( 214): at android.app.ActivityThread.access$2200( ActivityThread.java:119) E/AndroidRuntime( 214): at android.app.ActivityThread$H.handleMessage( ActivityThread.java:1863) E/AndroidRuntime( 214): at android.os.Handler.dispatchMessage(Handler.java:99) E/AndroidRuntime( 214): at android.os.Looper.loop(Looper.java:123) E/AndroidRuntime( 214): at android.app.ActivityThread.main(ActivityThread.java:4363) E/AndroidRuntime( 214): at java.lang.reflect.Method.invokeNative(Native Method) E/AndroidRuntime( 214): at java.lang.reflect.Method.invoke(Method.java:521) E/AndroidRuntime( 214): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run( ZygoteInit.java:860) E/AndroidRuntime( 214): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) E/AndroidRuntime( 214): at dalvik.system.NativeStart.main(Native Method) E/AndroidRuntime( 214): Caused by: java.lang.NullPointerException E/AndroidRuntime( 214): at com.aschyiel.disp.Disp.onCreate(Disp.java:66) E/AndroidRuntime( 214): at android.app.Instrumentation.callActivityOnCreate( Instrumentation.java:1047) E/AndroidRuntime( 214): at android.app.ActivityThread.performLaunchActivity( ActivityThread.java:2459) E/AndroidRuntime( 214): ... 11 more 发生错误的示例代码如下： import ... public class Disp extends Activity { private TextView foo; @Override public void onCreate( Bundle savedInstanceState ) { ... foo.setText("bar"); } }

上述代码失败原因是忘记使用findViewById()。下面是修复后的代码：

import ... public class Disp extends Activity { private TextView foo; @Override public void onCreate( Bundle savedInstanceState ) { ... foo = (TextView) findViewById( R.id.id_foo ); foo.setText("bar"); } }

这段代码应该会去除错误。3.6.4 参阅 “Google I/O 2009-Debugging Arts of the Ninja Masters”（Google I/O 2009-忍者大师的调试艺术）

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