java - setTypeface 空指针异常

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);，即使我切换了其起源的最后两行的位置，它也会收到 NullPointerException我寻找了很长时间后找不到。 (在 stackoverflow 上搜索答案也是如此)您知道导致此错误的原因吗？可以帮我指出吗？

Answer 1

您忘记为您的 Activity 提供布局。你必须打电话

setContentView(R.layout.activity)

An activity is a single, focused thing that the user can do. Almost all activities interact with the user, so the Activity class takes care of creating a window for you in which you can place your UI with setContentView(View).

您可以阅读更多here .