Question

这是一个简单的应用程序，它使用okkhttp从forecast.io获取预测只有当我声明文本视图并尝试将其文本设置为温度时，才会出现此问题。这是活动：

public class MainActivity extends Activity {
private static String TAG = MainActivity.class.getSimpleName();
TextView temperatureTextView =(TextView) findViewById(R.id.temperatureTextView);


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    //https://api.forecast.io/forecast/APIKEY/LATITUDE,LONGITUDE,TIME

    String apiKey = "29cfca9514567f6ac466b782adea8a2d";
    double latitude =37.8267;
    double longitude = -122.423;
    if (isNetworkAvailable()) {
        OkHttpClient client = new OkHttpClient();


        String forecastUrl = "https://api.forecast.io/forecast/" + apiKey + "/" + latitude + "," + longitude;
        Request request = new Request.Builder()
                .url(forecastUrl)
                .build();
        client.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Request request, IOException e) {

            }

            @Override
            public void onResponse(Response response) throws IOException {
                try {
                    final String jsonData = response.body().string();
                    Log.v(TAG, jsonData);
                    if (response.isSuccessful()) {

                        Log.v(TAG , "request successful");
                        final CurrentWeather currentWeather = currentWeather(jsonData);
                        runOnUiThread(new Runnable() {
                            @Override
                            public void run() {

                                temperatureTextView.setText(currentWeather.getTemperature()+"");
                            }
                        });


                    } else {
                        alertDialog("Aw, Snap!","There was a problem with the request. Please try again later.");
                    }

                } catch (IOException e) {
                    Log.e(TAG, "Exception caught");
                }


            }

        });
    }
    else {
            alertDialog("Aw, Snap!","Please make sure you are connected to the internet.");
    }
}

这是清单：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.ironman.stormy" >
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name"
            android:screenOrientation="portrait">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

这是日志：

04-27 02:41:48.376  24123-24123/com.example.ironman.stormy E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.ironman.stormy/com.example.ironman.stormy.MainActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java)
            at android.app.ActivityThread.access$600(ActivityThread.java)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java)
            at android.os.Handler.dispatchMessage(Handler.java)
            at android.os.Looper.loop(Looper.java)
            at android.app.ActivityThread.main(ActivityThread.java)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at android.app.Activity.findViewById(Activity.java)
            at com.example.ironman.stormy.MainActivity.<init>(MainActivity.java:36)
            at java.lang.Class.newInstanceImpl(Native Method)
            at java.lang.Class.newInstance(Class.java:1319)
            at android.app.Instrumentation.newActivity(Instrumentation.java)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java)
            at android.app.ActivityThread.access$600(ActivityThread.java)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java)
            at android.os.Handler.dispatchMessage(Handler.java)
            at android.os.Looper.loop(Looper.java)
            at android.app.ActivityThread.main(ActivityThread.java)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java)
            at dalvik.system.NativeStart.main(Native Method)

Answer 1

在findViewById之后调用setContentView才有意义。移动电话。

（另请注意，如果在您旋转屏幕后HTTP响应到达，则文本字段不会更新。但这是另一个故事。）

java.lang.RuntimeException：更新textview时无法实例化活动

1 个答案: