android - Handler.post Android 上的错误

Question

我有这段代码可以返回天气图像，但我有这个错误:

java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.os.Handler.post(java.lang.Runnable)' on a null object reference at example.example.run(Logo.java:112)

这是我遇到错误的函数:

    private void updateWeatherData(final String city) {
            new Thread() {
                public void run() {
                    final JSONObject json = RemoteFetch.getJSON(getActivity(), city);
                    if (json == null) {
                        handler.post(new Runnable() {
                            public void run() {
                                Toast.makeText(getActivity(),
                                        getActivity().getString(R.string.place_not_found),
                                        Toast.LENGTH_LONG).show();
                            }
                        });
                    } else {
  error where ----->   handler.post(new Runnable() {
                            public void run() {
                                renderWeather(json);
                            }
                        });
                    }
                }
            }.start();
        }

Answer 1

NullPointerException: Attempt to invoke virtual method 'boolean android.os.Handler.post(java.lang.Runnable)' on a null object reference

表示 handler 为 null。

在调用post 方法之前初始化handler 对象:

handler=new Handler();