为什么空指针异常啊

为什么空指针错误啊？？？
问题：我用debug测试的时候categoryArray[i]明明有值啊，可是为什么就是传不到list里面呢？

log：

Java code

06-14 09:33:00.830: E/AndroidRuntime(736): FATAL EXCEPTION: main06-14 09:33:00.830: E/AndroidRuntime(736): java.lang.RuntimeException: Unable to start activity ComponentInfo{napo.news.activity/napo.news.activity.WenpingNewsActivity}: java.lang.NullPointerException06-14 09:33:00.830: E/AndroidRuntime(736):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)06-14 09:33:00.830: E/AndroidRuntime(736):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)06-14 09:33:00.830: E/AndroidRuntime(736):     at android.app.ActivityThread.access$2300(ActivityThread.java:125)06-14 09:33:00.830: E/AndroidRuntime(736):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)06-14 09:33:00.830: E/AndroidRuntime(736):     at android.os.Handler.dispatchMessage(Handler.java:99)06-14 09:33:00.830: E/AndroidRuntime(736):     at android.os.Looper.loop(Looper.java:123)06-14 09:33:00.830: E/AndroidRuntime(736):     at android.app.ActivityThread.main(ActivityThread.java:4627)06-14 09:33:00.830: E/AndroidRuntime(736):     at java.lang.reflect.Method.invokeNative(Native Method)06-14 09:33:00.830: E/AndroidRuntime(736):     at java.lang.reflect.Method.invoke(Method.java:521)06-14 09:33:00.830: E/AndroidRuntime(736):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)06-14 09:33:00.830: E/AndroidRuntime(736):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)06-14 09:33:00.830: E/AndroidRuntime(736):     at dalvik.system.NativeStart.main(Native Method)06-14 09:33:00.830: E/AndroidRuntime(736): Caused by: java.lang.NullPointerException06-14 09:33:00.830: E/AndroidRuntime(736):     at napo.news.activity.WenpingNewsActivity.onCreate(WenpingNewsActivity.java:55)06-14 09:33:00.830: E/AndroidRuntime(736):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)06-14 09:33:00.830: E/AndroidRuntime(736):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)06-14 09:33:00.830: E/AndroidRuntime(736):     ... 11 more

java代码：

Java code

package napo.news.activity;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import napo.news.util.DensityUtil;import android.app.Activity;import android.os.Bundle;import android.view.Gravity;import android.view.ViewGroup.LayoutParams;import android.widget.GridView;import android.widget.LinearLayout;import android.widget.SimpleAdapter;public class WenpingNewsActivity extends Activity {    private final int COLUMNWIDTHPX = 55;    private int mColumnWidthDip;    /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);        mColumnWidthDip = DensityUtil.px2dip(this, COLUMNWIDTHPX);        String[] categoryArray = getResources().getStringArray(                R.array.categories);        List<HashMap<String, String>> categories = new ArrayList<HashMap<String, String>>();        for (int i=0; i < categoryArray.length; i++) {            HashMap<String, String> hashMap = new HashMap<String, String>();            hashMap.put("category_title", categoryArray[i]);            categories.add(hashMap);        }                SimpleAdapter categoryAdapter = new SimpleAdapter(this, categories, R.layout.category_title, new String[]{"category_title"}, new int[] {R.id.category_title});        GridView category = new GridView(this);        category.setColumnWidth(mColumnWidthDip);        category.setNumColumns(GridView.AUTO_FIT);        category.setGravity(Gravity.CENTER);                int width = mColumnWidthDip * categories.size();        LayoutParams params = new LayoutParams(width,                LayoutParams.WRAP_CONTENT);        category.setLayoutParams(params);        category.setAdapter(categoryAdapter);                LinearLayout categoryList = (LinearLayout)findViewById(R.id.catgory_layout);        categoryList.addView(category);    }} 
 

[解决办法]
你打断点跟踪一下啊。
[解决办法]
你定义 private int mColumnWidthDip;直接定义成 private int mColumnWidthDip=0;不就行了吗



[解决办法]

Java code

06-14 09:33:00.830: E/AndroidRuntime(736): Caused by: java.lang.NullPointerException06-14 09:33:00.830: E/AndroidRuntime(736):     at napo.news.activity.WenpingNewsActivity.onCreate(WenpingNewsActivity.java:55)
[解决办法]
探讨


Java code

06-14 09:33:00.830: E/AndroidRuntime(736): Caused by: java.lang.NullPointerException
06-14 09:33:00.830: E/AndroidRuntime(736):     at napo.news.activity.WenpingNewsActivity.onCreate(Wenp……

[解决办法]
空指针异常都搞不定的 肯定是初学者
[解决办法]
3楼，4楼回答是正解。
5楼要耐心，初学者也是变成老鸟的
[解决办法]
建议楼主，发错误提示及源码时，要发最新的错误提示及源码。

你目前发的出错是55行，代码却没有55行。
[解决办法]
打印下String数组，看是否有值的
[解决办法]
你进行单步调试吧，在提示的位置打上断点，并且利用eclipse自带的variables查看参数的值，或者对某个参数右键，然后选择watch就能进行观察，一步一步的你就会发现为什么，或者到哪一步的时候出现了错误，或者和你原来想的不一样了。编译器有时候和我们的大脑思考的运行肯定不一样的！加油吧，一起学习！
[解决办法]
这是不可能的
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我用断点测试到这一行代码出问题了：category.setAdapter(categoryAdapter);
categoryAdapter有值，但category里却没有值，为什么啊？
引用:

savedInstanceState 是 null值，这是什么原因啊？
 

 

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