方法调用可能会产生 java.lang.nullpointerexception
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method invocation may produce java.lang.nullpointerexception
提问by Mohamad Mustafa
When I try to run this, the emulator crashes and I get this Exception
当我尝试运行它时，模拟器崩溃并出现此异常
method invocation may produce java.lang.nullpointerexception
方法调用可能会产生 java.lang.nullpointerexception
Here is my code, I know the error is in the last line but I don't know how to fix it
这是我的代码，我知道错误在最后一行，但我不知道如何修复它
import android.os.StrictMode;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;
import java.net.MalformedURLException;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy);
// FIXME: Experimenting
try {
ReadingFactory parser = new BOMFactory();
WeatherService s = new WeatherService(
"BOM", "http://www.bom.gov.au/fwo/IDV60801/IDV60801.94839.json", parser
);
s.run();
// Thread test = new Thread(s);
// test.start();
} catch (MalformedURLException e) {
e.printStackTrace();
}
BOMResponse bomResponse = new BOMResponse();
TextView temperature = (TextView)findViewById(R.id.temperature);
temperature.setText(String.format("%d", bomResponse.getObservations().getData().get(0).getAirTemp().toString()));
}
}
Here is my complete Stacktrace
这是我完整的 Stacktrace
FATAL EXCEPTION: main
Process: com.example.teamredrmit.weatherapp, PID: 1792
java.lang.RuntimeException: Unable to start activity
ComponentInfo{com.example.teamredrmit.weatherapp/com.example.teamredrmit.weathe
app.MainActivity}: java.lang.NullPointerException at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233) at android.app.ActivityThread.access0(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5001)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.example.teamredrmit.weatherapp.MainActivity.onCreate(MainActivity.java:41)
at android.app.Activity.performCreate(Activity.java:5231)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2148)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)?
at android.app.ActivityThread.access0(ActivityThread.java:135)?
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)?
at android.os.Handler.dispatchMessage(Handler.java:102)?
at android.os.Looper.loop(Looper.java:136)?
at android.app.ActivityThread.main(ActivityThread.java:5001)?
at java.lang.reflect.Method.invokeNative(Native Method)?
at java.lang.reflect.Method.invoke(Method.java:515)?
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)?
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)?
at dalvik.system.NativeStart.main(Native Method)
回答by KDeogharkar
BOMResponse bomResponse = new BOMResponse();
TextView temperature = (TextView)findViewById(R.id.temperature);
temperature.setText(String.format("%d", bomResponse.getObservations().getData().get(0).getAirTemp().toString()));
here you are just initializing your BOMResponseobject . you are not setting value inside your custom object so bomResponse.getObservations()will be null. you have to set value first then use it.
在这里，您只是在初始化您的BOMResponse对象。你没有设置你的自定义对象的内在价值，从而 bomResponse.getObservations()会null。你必须先设置值然后使用它。
