android - 致命异常: main Android

Question

当我运行我的代码时，它可以工作几秒钟并自动关闭。它显示消息不幸的是您的应用已关闭。在我添加了带有按钮的布局之后，这开始发生。

这是我的原木猫

   07-21 04:41:14.320: E/AndroidRuntime(1764): FATAL EXCEPTION: main
07-21 04:41:14.320: E/AndroidRuntime(1764): Process: com.example.adaderana, PID: 1764
07-21 04:41:14.320: E/AndroidRuntime(1764): java.lang.NullPointerException
07-21 04:41:14.320: E/AndroidRuntime(1764):     at com.example.adaderana.MainActivity$DownloadJSON.onPostExecute(MainActivity.java:140)
07-21 04:41:14.320: E/AndroidRuntime(1764):     at com.example.adaderana.MainActivity$DownloadJSON.onPostExecute(MainActivity.java:1)
07-21 04:41:14.320: E/AndroidRuntime(1764):     at android.os.AsyncTask.finish(AsyncTask.java:632)
07-21 04:41:14.320: E/AndroidRuntime(1764):     at android.os.AsyncTask.access$600(AsyncTask.java:177)
07-21 04:41:14.320: E/AndroidRuntime(1764):     at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
07-21 04:41:14.320: E/AndroidRuntime(1764):     at android.os.Handler.dispatchMessage(Handler.java:102)
07-21 04:41:14.320: E/AndroidRuntime(1764):     at android.os.Looper.loop(Looper.java:137)
07-21 04:41:14.320: E/AndroidRuntime(1764):     at android.app.ActivityThread.main(ActivityThread.java:4998)
07-21 04:41:14.320: E/AndroidRuntime(1764):     at java.lang.reflect.Method.invokeNative(Native Method)
07-21 04:41:14.320: E/AndroidRuntime(1764):     at java.lang.reflect.Method.invoke(Method.java:515)
07-21 04:41:14.320: E/AndroidRuntime(1764):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
07-21 04:41:14.320: E/AndroidRuntime(1764):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
07-21 04:41:14.320: E/AndroidRuntime(1764):     at dalvik.system.NativeStart.main(Native Method)
07-21 04:41:14.350: W/ActivityManager(371):   Force finishing activity com.example.adaderana/.MainActivity
07-21 04:41:14.390: D/gralloc(51): Registering a buffer in the process that created it. This may cause memory ordering problems.
07-21 04:41:14.390: E/libEGL(51): called unimplemented OpenGL ES API
07-21 04:41:14.390: E/libEGL(51): called unimplemented OpenGL ES API
07-21 04:41:14.390: E/libEGL(51): called unimplemented OpenGL ES API
07-21 04:41:14.390: E/libEGL(51): called unimplemented OpenGL ES API
07-21 04:41:14.390: E/SurfaceFlinger(51): glCheckFramebufferStatusOES error 1717000432
07-21 04:41:14.390: E/SurfaceFlinger(51): got GL_FRAMEBUFFER_COMPLETE_OES error while taking screenshot
07-21 04:41:14.400: E/libEGL(51): called unimplemented OpenGL ES API
07-21 04:41:14.400: E/libEGL(51): called unimplemented OpenGL ES API
07-21 04:41:14.400: W/WindowManager(371): Screenshot failure taking screenshot for (246x410) to layer 21015
07-21 04:41:14.710: I/Choreographer(371): Skipped 56 frames!  The application may be doing too much work on its main thread.
07-21 04:41:14.990: W/ActivityManager(371): Activity pause timeout for ActivityRecord{b3edf2f8 u0 com.example.adaderana/.MainActivity t16 f}
07-21 04:41:15.010: I/Choreographer(371): Skipped 38 frames!  The application may be doing too much work on its main thread.
07-21 04:41:15.370: I/Choreographer(371): Skipped 37 frames!  The application may be doing too much work on its main thread.
07-21 04:41:15.420: I/Choreographer(371): Skipped 109 frames!  The application may be doing too much work on its main thread.
07-21 04:41:15.430: I/Choreographer(534): Skipped 75 frames!  The application may be doing too much work on its main thread.
07-21 04:41:18.560: I/Choreographer(371): Skipped 30 frames!  The application may be doing too much work on its main thread.
07-21 04:41:18.780: I/Choreographer(371): Skipped 54 frames!  The application may be doing too much work on its main thread.
07-21 04:41:19.080: I/Choreographer(371): Skipped 40 frames!  The application may be doing too much work on its main thread.
07-21 04:41:19.320: I/Choreographer(371): Skipped 58 frames!  The application may be doing too much work on its main thread.
07-21 04:41:19.520: I/Choreographer(371): Skipped 52 frames!  The application may be doing too much work on its main thread.
07-21 04:41:29.710: W/ActivityManager(371): Activity destroy timeout for ActivityRecord{b3edf2f8 u0 com.example.adaderana/.MainActivity t16 f}

我的主要 Activity

package com.example.adaderana;

import java.util.ArrayList;
import java.util.HashMap;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
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.ListView;



public class MainActivity extends Activity  {
    // Declare Variables
    JSONObject jsonobject;
    JSONArray jsonarray;
    ListView listview;
    ListViewAdapter adapter;
    ProgressDialog mProgressDialog;
    ArrayList<HashMap<String, String>> arraylist;





    static String TITLE = "title";
    static String AUTHOR = "author";
    static String THUMBNAIL = "thumbnail";
    static String CONTENTS = "contents";
    static String IMAGE = "image";




    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // Get the view from list_main.xml
        setContentView(R.layout.button);


        Button b = (Button) findViewById(R.id.button2);
        b.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                Intent myIntent = new Intent(MainActivity.this, Video.class);
                startActivityForResult(myIntent, 0);


             //  new DownloadJSON().execute();
            }
        });


        Button a = (Button) findViewById(R.id.button1);

        a.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {

              // TODO Auto-generated method stub
              new DownloadJSON().execute();
            }
        });



        // Execute DownloadJSON AsyncTask
   // new DownloadJSON().execute();

}
   // DownloadJSON AsyncTask
    private class DownloadJSON extends AsyncTask<Void, Void, Void> {


 @Override
        protected void onPreExecute() {
            super.onPreExecute();
            // Create a progressdialog
            mProgressDialog = new ProgressDialog(MainActivity.this);
            // Set progressdialog title
            mProgressDialog.setTitle("Derana News");
            // Set progressdialog message
            mProgressDialog.setMessage("Loading...");
            mProgressDialog.setIndeterminate(false);
            // Show progressdialog
            mProgressDialog.show();
        }


        @Override
        protected Void doInBackground(Void... params) {
            // Create an array
            arraylist = new ArrayList<HashMap<String, String>>();
            // Retrieve JSON Objects from the given URL address
            jsonobject = JSONfunctions
                    .getJSONfromURL("http://www.adaderana.mobi/apple/ipad.php?q=topcat&cat=36");

            try {
                // Locate the array name in JSON
                jsonarray = jsonobject.getJSONArray("TopNewsGivenCat");

                for (int i = 0; i < jsonarray.length(); i++) {
                    HashMap<String, String> map = new HashMap<String, String>();
                    jsonobject = jsonarray.getJSONObject(i);
                    // Retrive JSON Objects
                    map.put("title", jsonobject.getString("title"));
                    map.put("author", jsonobject.getString("author"));
                    map.put("thumbnail", jsonobject.getString("thumbnail"));
                    map.put("contents", jsonobject.getString("contents"));
                    map.put("image", jsonobject.getString("image"));

                    // Set the JSON Objects into the array
                    arraylist.add(map);
                }
            } catch (JSONException e) {
                Log.e("Error", e.getMessage());
                e.printStackTrace();
            }
            return null;
        }

        @Override
        protected void onPostExecute(Void args) {
            // Locate the listview in listview_main.xml
            listview = (ListView) findViewById(R.id.listview);
            // Pass the results into ListViewAdapter.java
            adapter = new ListViewAdapter(MainActivity.this, arraylist);
            // Set the adapter to the ListView
            listview.setAdapter(adapter);
            // Close the progressdialog
            mProgressDialog.dismiss();
        }
    }
}

Answer 1

您正在将按钮布局设置为内容setContentView(R.layout.button);没有listview作为您的评论说// Locate the listview in listview_main.xml
那么findViewById(R.id.listview);如何获得listview？
请修复您的xml，并在onCreate()上使用listview = (ListView) findViewById(R.id.listview);。