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                        /Android面试常客Handler详解

为什么这里不写sleep会在sendMessage这行报空指针错误？

05-19 09:37:34.193 1625-1625/com.geekband.handlerdemo01 E/AndroidRuntime: FATAL EXCEPTION: main

Process: com.geekband.handlerdemo01, PID: 1625

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.geekband.handlerdemo01/com.geekband.handlerdemo01.SencondActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.os.Handler.sendEmptyMessage(int)' on a null object reference

at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)

at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)

at android.app.ActivityThread.-wrap11(ActivityThread.java)

at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)

at android.os.Handler.dispatchMessage(Handler.java:102)

at android.os.Looper.loop(Looper.java:148)

at android.app.ActivityThread.main(ActivityThread.java:5417)

at java.lang.reflect.Method.invoke(Native Method)

at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)

at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.os.Handler.sendEmptyMessage(int)' on a null object reference

at com.geekband.handlerdemo01.SencondActivity.onCreate(SencondActivity.java:51)

at android.app.Activity.performCreate(Activity.java:6237)

at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)

at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)

at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)

at android.app.ActivityThread.-wrap11(ActivityThread.java)

at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)

at android.os.Handler.dispatchMessage(Handler.java:102)

at android.os.Looper.loop(Looper.java:148)

at android.app.ActivityThread.main(ActivityThread.java:5417)

at java.lang.reflect.Method.invoke(Native Method)

at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)

at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

上面是错误报告

嗟嗟嗟

2016-05-19

源自：Android面试常客Handler详解 5-1

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3 回答

喜得温词
2017-08-10

Handler对象没有实例化吧

1 回复有任何疑惑可以回复我~

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慕粉3126759
2016-11-03

注意到子线程中 handler一开始是没有实例化的实例化在start()中进行，所以在执行thread.start()后，直接执行thread.handler.send...方法此时也许thread.start()中还未执行到给handler实例化的那一步，自然抛出异常，解决方法之二就是在thread中定义handler时候直接实例化应该就没有问题了的