ButterKnife運行時Caused by: java.lang.IllegalStateException異常

問題

在使用ButterKnife時，一不注意犯了個錯誤，如下：

Caused by: 
java.lang.IllegalStateException: Required view 'btn_camera' with ID 2131427422 for field 'btnCamera' was not found. If this view is optional add '@Nullable' (fields) or '@Optional' (methods) annotation.
                                                       at butterknife.internal.Utils.findRequiredView(Utils.java:92)
                                                       at butterknife.internal.Utils.findRequiredViewAsType(Utils.java:104)
                                                       at com.liuw.camera.MainActivity_ViewBinding.<init>(MainActivity_ViewBinding.java:25)
                                                       at java.lang.reflect.Constructor.constructNative(Native Method)
                                                       at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
                                                       at butterknife.ButterKnife.createBinding(ButterKnife.java:199)
                                                       at butterknife.ButterKnife.bind(ButterKnife.java:124)
                                                       at com.liuw.camera.MainActivity.onCreate(MainActivity.java:51)
                                                       at android.app.Activity.performCreate(Activity.java:5349)
                                                       at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1100)
                                                       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2170)
                                                       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2255) 
                                                       at android.app.ActivityThread.access$800(ActivityThread.java:143) 
                                                       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1204) 
                                                       at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                       at android.os.Looper.loop(Looper.java:136) 
                                                       at android.app.ActivityThread.main(ActivityThread.java:5114) 
                                                       at java.lang.reflect.Method.invokeNative(Native Method) 
                                                       at java.lang.reflect.Method.invoke(Method.java:515) 
                                                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 
                                                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:602) 
                                                       at dalvik.system.NativeStart.main(Native Method)

原因

造成這個問題的原因是在SetContentView之前就寫了ButterKnife.bind(this)，正確寫法應該是在setContentView之後才寫,切記，切記！