Android WearのButtonでsetOnClickListenerはonLayoutInflatedの中でやらなければならない

ずっと`onCreate`に書いてクラッシュし続けてたら間違ってたのでメモ。

# setOnClickListenerはonCreateに書いてはならない
下記のようなエラーでクラッシュします。

```error:terminal
E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: net.furusin.www.whereiswear, PID: 25720
                  java.lang.RuntimeException: Unable to start activity ComponentInfo{net.furusin.www.whereiswear/net.furusin.www.whereiswear.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
                      at android.app.ActivityThread.-wrap11(ActivityThread.java)
                      at android.app.ActivityThread$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:5422)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                   Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                      at net.furusin.www.whereiswear.MainActivity.onCreate(MainActivity.java:31)
                      at android.app.Activity.performCreate(Activity.java:6251)
                      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$H.handleMessage(ActivityThread.java:1344) 
                      at android.os.Handler.dispatchMessage(Handler.java:102) 
                      at android.os.Looper.loop(Looper.java:148) 
                      at android.app.ActivityThread.main(ActivityThread.java:5422) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
```

## 対処方法
`onLayoutInflated`の中でやらなければならない。

```java:MainActivity.java
        stub.setOnLayoutInflatedListener(new WatchViewStub.OnLayoutInflatedListener() {
            @Override
            public void onLayoutInflated(WatchViewStub stub) {
                Button button = (Button) stub.findViewById(R.id.button);
                button.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        // do something.
                    }
                });
            }
        });
```

以上。