Android:当我试图从网站检索信息时，为什么我的android应用程序显示一个空布局，然后崩溃？
Android:当我试图从网站检索信息时，为什么我的android应用程序显示一个空布局，然后崩溃？
提问于 2017-07-07 12:18:10
我正在尝试检索一个网站的源代码，但我的应用程序既不显示我的gui，也不打印到日志。
这是我的代码。
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.concurrent.ExecutionException;
public class MainActivity extends AppCompatActivity {
public class DownloadTask extends AsyncTask<String, Void, String> {
@Override
protected String doInBackground(String... urls) {
String result = "";
URL url;
HttpURLConnection urlConnection = null;
try{
url = new URL(urls[0]);
urlConnection = (HttpURLConnection)url.openConnection();
InputStream in = urlConnection.getInputStream();
InputStreamReader reader = new InputStreamReader(in);
int data = reader.read(); //start reading inputstream reader
while(data!=-1){
char current = (char) data;
result += current;
data = reader.read();
}
return result;
}
catch (Exception e){
e.printStackTrace();
return null;
}
}
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
DownloadTask task = new DownloadTask();
String result = null;
try {
result = task.execute("https://www.therichest.com/top-lists/top-100-richest-celebrities").get();
Log.i("Contents of the url:", result);
}
catch (InterruptedException e) {
e.printStackTrace();
}
catch (ExecutionException e) {
e.printStackTrace();
}
}}
这就是我的日志中显示的内容
07-06 21:08:01.020 2025-2025/? I/art: Late-enabling -Xcheck:jni
07-06 21:08:01.050 2025-2031/? I/art: Debugger is no longer active
07-06 21:08:01.082 2025-2025/? W/System: ClassLoader referenced unknown path: /data/app/com.example.jimmy.guesstherich-1/lib/arm
07-06 21:08:01.116 2025-2025/? W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
07-06 21:08:01.138 2025-2025/? D/PhoneWindowEx: [PWEx][generateLayout] setLGNavigationBarColor : colors=0xff000000
07-06 21:08:01.138 2025-2025/? I/PhoneWindow: [setLGNavigationBarColor] color=0x ff000000
07-06 21:08:01.233 2025-2039/? D/libc: skt_base:0, kt_base:0, mptcp_enabled:0, socks_enabled:0, wifi_connected:1
07-06 21:08:01.234 2025-2039/? D/libc: skt_base:0, kt_base:0, mptcp_enabled:0, socks_enabled:0, wifi_connected:1
07-06 21:08:32.295 2025-2039/com.example.jimmy.guesstherich W/System.err: java.net.ConnectException: failed to connect to www.therichest.com/34.202.89.146 (port 443): connect failed: ETIMEDOUT (Connection timed out)
07-06 21:08:32.295 2025-2039/com.example.jimmy.guesstherich W/System.err: at libcore.io.IoBridge.connect(IoBridge.java:124)
07-06 21:08:32.295 2025-2039/com.example.jimmy.guesstherich W/System.err: at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:183)
07-06 21:08:32.295 2025-2039/com.example.jimmy.guesstherich W/System.err: at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:452)
07-06 21:08:32.295 2025-2039/com.example.jimmy.guesstherich W/System.err: at java.net.Socket.connect(Socket.java:888)
07-06 21:08:32.295 2025-2039/com.example.jimmy.guesstherich W/System.err: at com.android.okhttp.internal.Platform.connectSocket(Platform.java:117)
07-06 21:08:32.296 2025-2039/com.example.jimmy.guesstherich W/System.err: at com.android.okhttp.internal.http.SocketConnector.connectRawSocket(SocketConnector.java:188)
07-06 21:08:32.296 2025-2039/com.example.jimmy.guesstherich W/System.err: at com.android.okhttp.internal.http.SocketConnector.connectTls(SocketConnector.java:99)
07-06 21:08:32.296 2025-2039/com.example.jimmy.guesstherich W/System.err: at com.android.okhttp.Connection.connect(Connection.java:151)
07-06 21:08:32.296 2025-2039/com.example.jimmy.guesstherich W/System.err: at com.android.okhttp.Connection.connect(Connection.java:187)
07-06 21:08:32.296 2025-2039/com.example.jimmy.guesstherich W/System.err: at com.android.okhttp.Connection.connectAndSetOwner(Connection.java:238)
07-06 21:08:32.296 2025-2039/com.example.jimmy.guesstherich W/System.err: at com.android.okhttp.OkHttpClient$1.connectAndSetOwner(OkHttpClient.java:134)
07-06 21:08:32.296 2025-2039/com.example.jimmy.guesstherich W/System.err: at com.android.okhttp.internal.http.HttpEngine.nextConnection(HttpEngine.java:384)
07-06 21:08:32.296 2025-2039/com.example.jimmy.guesstherich W/System.err: at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:371)
07-06 21:08:32.296 2025-2039/com.example.jimmy.guesstherich W/System.err: at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:289)
07-06 21:08:32.296 2025-2039/com.example.jimmy.guesstherich W/System.err: at com.android.okhttp.internal.huc.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:457)
07-06 21:08:32.296 2025-2039/com.example.jimmy.guesstherich W/System.err: at com.android.okhttp.internal.huc.HttpURLConnectionImpl.getResponse(HttpURLConnectionImpl.java:408)
07-06 21:08:32.296 2025-2039/com.example.jimmy.guesstherich W/System.err: at com.android.okhttp.internal.huc.HttpURLConnectionImpl.getInputStream(HttpURLConnectionImpl.java:247)
07-06 21:08:32.296 2025-2039/com.example.jimmy.guesstherich W/System.err: at com.android.okhttp.internal.huc.DelegatingHttpsURLConnection.getInputStream(DelegatingHttpsURLConnection.java:210)
07-06 21:08:32.296 2025-2039/com.example.jimmy.guesstherich W/System.err: at com.android.okhttp.internal.huc.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java)
07-06 21:08:32.296 2025-2039/com.example.jimmy.guesstherich W/System.err: at com.example.jimmy.guesstherich.MainActivity$DownloadTask.doInBackground(MainActivity.java:29)
07-06 21:08:32.296 2025-2039/com.example.jimmy.guesstherich W/System.err: at com.example.jimmy.guesstherich.MainActivity$DownloadTask.doInBackground(MainActivity.java:15)
07-06 21:08:32.297 2025-2039/com.example.jimmy.guesstherich W/System.err: at android.os.AsyncTask$2.call(AsyncTask.java:295)
07-06 21:08:32.297 2025-2039/com.example.jimmy.guesstherich W/System.err: at java.util.concurrent.FutureTask.run(FutureTask.java:237)
07-06 21:08:32.297 2025-2039/com.example.jimmy.guesstherich W/System.err: at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234)
07-06 21:08:32.297 2025-2039/com.example.jimmy.guesstherich W/System.err: at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
07-06 21:08:32.297 2025-2039/com.example.jimmy.guesstherich W/System.err: at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
07-06 21:08:32.297 2025-2039/com.example.jimmy.guesstherich W/System.err: at java.lang.Thread.run(Thread.java:818)
07-06 21:08:32.297 2025-2039/com.example.jimmy.guesstherich W/System.err: Caused by: android.system.ErrnoException: connect failed: ETIMEDOUT (Connection timed out)
07-06 21:08:32.297 2025-2039/com.example.jimmy.guesstherich W/System.err: at libcore.io.Posix.connect(Native Method)
07-06 21:08:32.298 2025-2039/com.example.jimmy.guesstherich W/System.err: at libcore.io.BlockGuardOs.connect(BlockGuardOs.java:111)
07-06 21:08:32.298 2025-2039/com.example.jimmy.guesstherich W/System.err: at libcore.io.IoBridge.connectErrno(IoBridge.java:137)
07-06 21:08:32.298 2025-2039/com.example.jimmy.guesstherich W/System.err: at libcore.io.IoBridge.connect(IoBridge.java:122)
07-06 21:08:32.298 2025-2039/com.example.jimmy.guesstherich W/System.err: ... 26 more
07-06 21:08:32.299 2025-2025/com.example.jimmy.guesstherich D/AndroidRuntime: Shutting down VM它会显示30-45秒的空白屏幕，然后崩溃，日志打印以下内容
07-06 21:08:32.300 2025-2025/com.example.jimmy.guesstherich E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.jimmy.guesstherich, PID: 2025
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.jimmy.guesstherich/com.example.jimmy.guesstherich.MainActivity}: java.lang.NullPointerException: println needs a message
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2440)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2500)
at android.app.ActivityThread.access$900(ActivityThread.java:163)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1362)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5585)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:730)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:620)
Caused by: java.lang.NullPointerException: println needs a message
at android.util.Log.println_native(Native Method)
at android.util.Log.i(Log.java:160)
at com.example.jimmy.guesstherich.MainActivity.onCreate(MainActivity.java:67)
at android.app.Activity.performCreate(Activity.java:6279)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1108)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2393)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2500)
at android.app.ActivityThread.access$900(ActivityThread.java:163)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1362)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5585)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:730)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:620)知道这是怎么回事吗？
我是一个初学者，所以我为任何错误道歉。
我也在遵循一个视频教程，并有三次检查，一切都是一样的。他的作品完全没问题。如果重要的话，那就是Rob Percival的“完整的Android开发课程”。
提前谢谢，我很感激！
回答 2
Stack Overflow用户
发布于 2017-07-07 12:24:14
此行将始终返回null(因为asynktask是异步的)：
result = task.execute("https://www.therichest.com/top-lists/top-100-richest-celebrities").get();如果您尝试打印带有空对象的日志，则会导致崩溃。
布局为空是因为应用程序无法连接到网站，并接收到超时异常。
Stack Overflow用户
发布于 2017-07-07 13:15:22
您之所以面临这个问题，是因为您在浏览器中放入了错误URL检查url。
result = task.execute("https://www.therichest.com/top-lists/top-100-richest-celebrities").get();这是演示URL
result = task.execute("http://api.androidhive.info/contacts/").get();页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/44962480
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