setTypeface nullpointerexception

Question

我又遇到了另一个问题，这次更令人困惑：

public class MainActivity extends Activity {
    TextView cityData;
    TextView updatedData;
    TextView detailsData;
    TextView currentTemperatureData;
    TextView weatherIcon;
    Typeface weatherIcons;
    Handler handleWeather;

    public MainActivity() {
        handleWeather = new Handler();
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        cityData = (TextView)   findViewById(R.id.city_field);
        updatedData = (TextView) findViewById(R.id.updated_field);
        detailsData = (TextView) findViewById(R.id.details_field);
        currentTemperatureData = (TextView) findViewById(R.id.current_temperature_field);
        weatherIcon = (TextView) findViewById(R.id.weather_icon);

        weatherIcons = Typeface.createFromAsset(getAssets(), "weather.ttf"); //fonts found from https://github.com/erikflowers/weather-icons 
        weatherIcon.setTypeface(weatherIcons);

在这里，在这段代码中，我的错误在于weatherIcon.setTypeface(weatherIcons);，它接收到NullPointerException，即使我在长时间搜索后切换了其原点我找不到的最后两行的位置。 （同样在stackoverflow上搜索答案） 你知道是什么导致了这个错误吗？请你帮忙指出来吗？

Answer 1

您忘记为您的活动提供布局。你必须致电

setContentView(R.layout.activity)

  

活动是用户可以做的一件重点事。几乎   所有活动都与用户交互，因此Activity类占用   为您创建一个可以放置UI的窗口   的的setContentView（查看）

您可以阅读更多here。

Answer 2

尝试以下修改后的代码：

    public class MainActivity extends Activity {
        TextView cityData;
        TextView updatedData;
        TextView detailsData;
        TextView currentTemperatureData;
        TextView weatherIcon;
        Typeface weatherIcons;
        Handler handleWeather;

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_xml_file);

            cityData = (TextView)   findViewById(R.id.city_field);
            updatedData = (TextView) findViewById(R.id.updated_field);
            detailsData = (TextView) findViewById(R.id.details_field);
            currentTemperatureData = (TextView) findViewById(R.id.current_temperature_field);
            weatherIcon = (TextView) findViewById(R.id.weather_icon);

            weatherIcons = Typeface.createFromAsset(getAssets(), "weather.ttf"); //fonts found from https://github.com/erikflowers/weather-icons 
            weatherIcon.setTypeface(weatherIcons);