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在学习android时，我正在制作一个ICMP ping程序。我添加了一个 AsyncTask 线程来防止“主网络中的网络”，现在我的编程正在抛出这个运行时异常（标题中的那个）。我是安卓新手；如果你们能帮助我，那就太好了。这里有问题的 logcat 错误：

05-30 13:52:49.644: E/AndroidRuntime(620): FATAL EXCEPTION: main
05-30 13:52:49.644: E/AndroidRuntime(620): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.icmpping.Joe/com.icmpping.Joe.PingAppActivity}: java.lang.NullPointerException
05-30 13:52:49.644: E/AndroidRuntime(620):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1880)
05-30 13:52:49.644: E/AndroidRuntime(620):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
05-30 13:52:49.644: E/AndroidRuntime(620):  at android.app.ActivityThread.access$600(ActivityThread.java:123)
05-30 13:52:49.644: E/AndroidRuntime(620):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
05-30 13:52:49.644: E/AndroidRuntime(620):  at android.os.Handler.dispatchMessage(Handler.java:99)
05-30 13:52:49.644: E/AndroidRuntime(620):  at android.os.Looper.loop(Looper.java:137)
05-30 13:52:49.644: E/AndroidRuntime(620):  at android.app.ActivityThread.main(ActivityThread.java:4424)
05-30 13:52:49.644: E/AndroidRuntime(620):  at java.lang.reflect.Method.invokeNative(Native Method)
05-30 13:52:49.644: E/AndroidRuntime(620):  at java.lang.reflect.Method.invoke(Method.java:511)
05-30 13:52:49.644: E/AndroidRuntime(620):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
05-30 13:52:49.644: E/AndroidRuntime(620):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
05-30 13:52:49.644: E/AndroidRuntime(620):  at dalvik.system.NativeStart.main(Native Method)
05-30 13:52:49.644: E/AndroidRuntime(620): Caused by: java.lang.NullPointerException
05-30 13:52:49.644: E/AndroidRuntime(620):  at android.app.Activity.findViewById(Activity.java:1794)
05-30 13:52:49.644: E/AndroidRuntime(620):  at com.icmpping.Joe.PingAppActivity.<init>(PingAppActivity.java:15)
05-30 13:52:49.644: E/AndroidRuntime(620):  at java.lang.Class.newInstanceImpl(Native Method)
05-30 13:52:49.644: E/AndroidRuntime(620):  at java.lang.Class.newInstance(Class.java:1319)
05-30 13:52:49.644: E/AndroidRuntime(620):  at android.app.Instrumentation.newActivity(Instrumentation.java:1023)
05-30 13:52:49.644: E/AndroidRuntime(620):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1871)
05-30 13:52:49.644: E/AndroidRuntime(620):  ... 11 more

我很确定这与 AsyncTask 有关。ICMP_Ping.ping 方法来自另一个类，它返回一个字符串对象并接受一个字符串参数。它使用 java.net.InetAddress 和 System.currentTimeMillis()。无论如何，这是我的主要课程：

////

package com.icmpping.Joe;

import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class PingAppActivity extends Activity {

private TextView console = (TextView) findViewById(R.id.TEXT_STATUS_ID);

private OnClickListener listener = new OnClickListener() {
    public void onClick(View v) {

        Log.d("pingactivity", "Hey LOGCAT2");

        EditText urlbox = (EditText) findViewById(R.id.url_edittext);
        String url = urlbox.getText().toString();

        Log.d("pingactivity", "Hey LOGCAT3");
        new AsyncPing().execute(url);


        Log.d("pingactivity", "Hey LOGCAT4");
    }
};


public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    Log.d("pingactivity", "Hey LOGCAT0");

    Button pingbutton = (Button) findViewById(R.id.ping_button);

    pingbutton.setOnClickListener(listener);
    Log.d("pingactivity", "Hey LOGCAT1");

}


private class AsyncPing extends AsyncTask<String, Void, String> {

    @Override
    protected String doInBackground(String... url) {
        return ICMP_Ping.ping(url[0]);
    }

    //protected void onProgressUpdate(Integer... progress) {}

    protected void onPostExecute(String pingresult) {
        console.append(pingresult);

    }
}

}

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1 回答 1

3

这条线 TextView console = (TextView) findViewById(R.id.yourtextid);

放在后面setContentView(R.layout.main);

 

    TextView console;
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        Log.d("pingactivity", "Hey LOGCAT0");

        Button pingbutton = (Button) findViewById(R.id.ping_button);
        console = (TextView) findViewById(R.id.yourtextid);
    }
于 2012-05-30T14:45:30.823 回答