错误：

The specified child already has a parent. You must call removeView() on the child's parent first

    --------- beginning of crash
2019-11-08 15:54:27.646 9840-9840/com.example.mylayout E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.mylayout, PID: 9840
    java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.
        at android.view.ViewGroup.addViewInner(ViewGroup.java:4937)
        at android.view.ViewGroup.addView(ViewGroup.java:4768)
        at android.view.ViewGroup.addView(ViewGroup.java:4708)
        at android.view.ViewGroup.addView(ViewGroup.java:4681)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1466)
        at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1784)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1852)
        at android.support.v4.app.BackStackRecord.executeOps(BackStackRecord.java:802)
        at android.support.v4.app.FragmentManagerImpl.executeOps(FragmentManager.java:2625)
        at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2411)
        at android.support.v4.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManager.java:2366)
        at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:2273)
        at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:733)
        at android.os.Handler.handleCallback(Handler.java:790)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6494)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)

 仔细查了一下，发现我新加的fragment的

onCreateView 有不一样

原：

public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        view = inflater.inflate(R.layout.ssjk_fragment, container);
        return view;
    }

修改后：

public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        view = inflater.inflate(R.layout.ssjk_fragment, container,false);
        return view;
    }

解决问题！

参考：

https://www.cnblogs.com/seven-sky/p/4953343.html