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我想从可绘制文件夹中的图像列表动态创建自定义 ListView，但我得到空指针异常。有人能找出我的代码有什么问题吗？这是我的代码...

public class ImageSelectionActivity extends ListActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setListAdapter(new ImageAdapter(this));
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
    }
}

public class ImageAdapter extends BaseAdapter {
// a list of resource IDs for the images we want to display
private Integer[] images;

// a context so we can later create a view within it
private Context myContext;

// store a cache of resized bitmaps
// Note: we're not managing the cache size to ensure it doesn't 
// exceed any maximum memory usage requirements
private Bitmap[] cache;

private static LayoutInflater inflater=null;
private Activity activity;

    // Constructor
public ImageAdapter(Context c) {

    myContext = c;

    // Dynamically figure out which images we've imported
    // into the drawable folder, so we don't have to manually
    // type each image in to a fixed array.

    // obtain a list of all of the objects in the R.drawable class
    Field[] list = R.drawable.class.getFields();


    int count = 0, index = 0, j = list.length;

    // We first need to figure out how many of our images we have before
    // we can request the memory for an array of integers to hold their contents.

    // loop over all of the fields in the R.drawable class
    for(int i=0; i < j; i++)
        // if the name starts with img_ then we have one of our images!
        if(list[i].getName().startsWith("puzzle_")) count++;

    // We now know how many images we have. Reserve the memory for an 
    // array of integers with length 'count' and initialize our cache.
    images = new Integer[count];
    cache = new Bitmap[count];


    try {
        for(int i=0; i < j; i++)
            if(list[i].getName().startsWith("puzzle_")){
                images[index++] = list[i].getInt(null);
                }
    } catch(Exception e) {}


}

@Override
// the number of items in the adapter
public int getCount() {
    return images.length;
}

@Override
// not implemented, but normally would return 
// the object at the specified position
public Object getItem(int position) {
    return null;
}

@Override
// return the resource ID of the item at the current position
public long getItemId(int position) {
    return images[position];
}

// create a new ImageView when requested
@Override
public View getView(int position, View convertView, ViewGroup parent) {


    ImageView imgView = null;
    TextView textView;
    View itemView = convertView;        

    if(itemView == null) {
        inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        itemView  = inflater.inflate(R.layout.item_view, null);         
         imgView = (ImageView)itemView.findViewById(R.id.img_item);
         textView = (TextView)itemView.findViewById(R.id.text_item);
         textView.setText("Hello");


    }


    // see if we've stored a resized thumb in cache
    if(cache[position] == null) {

        // create a new Bitmap that stores a resized
        // version of the image we want to display. 
        BitmapFactory.Options options = new BitmapFactory.Options();
        options.inSampleSize = 4;
        Bitmap thumb = BitmapFactory.decodeResource(myContext.getResources(), images[position], options);

        // store the resized thumb in a cache so we don't have to re-generate it
        cache[position] = thumb;
    }

    // use the resized image we have in the cache
    imgView.setImageBitmap(cache[position]);


    return itemView;
}


}

这是 CatLog 跟踪：

    06-21 13:00:12.738: W/dalvikvm(30020): threadid=1: thread exiting with uncaught exception (group=0x413702a0)
06-21 13:00:12.743: E/AndroidRuntime(30020): FATAL EXCEPTION: main
06-21 13:00:12.743: E/AndroidRuntime(30020): java.lang.NullPointerException
06-21 13:00:12.743: E/AndroidRuntime(30020):    at com.binay.project.ImageAdapter.getView(ImageAdapter.java:101)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.widget.AbsListView.obtainView(AbsListView.java:2472)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.widget.ListView.makeAndAddView(ListView.java:1775)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.widget.ListView.fillDown(ListView.java:678)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.widget.ListView.fillFromTop(ListView.java:739)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.widget.ListView.layoutChildren(ListView.java:1628)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.widget.AbsListView.onLayout(AbsListView.java:2307)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.view.View.layout(View.java:14072)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.view.ViewGroup.layout(ViewGroup.java:4657)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.widget.FrameLayout.onLayout(FrameLayout.java:448)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.view.View.layout(View.java:14072)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.view.ViewGroup.layout(ViewGroup.java:4657)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1655)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1513)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.widget.LinearLayout.onLayout(LinearLayout.java:1426)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.view.View.layout(View.java:14072)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.view.ViewGroup.layout(ViewGroup.java:4657)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.widget.FrameLayout.onLayout(FrameLayout.java:448)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.view.View.layout(View.java:14072)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.view.ViewGroup.layout(ViewGroup.java:4657)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2004)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1825)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1120)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4604)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.view.Choreographer.doCallbacks(Choreographer.java:555)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.view.Choreographer.doFrame(Choreographer.java:525)
06-21 13:00:12.743: E/AndroidRuntime(30020):    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711)
4

2 回答 2

0

嗯，NPE 在第 101 行，应该是

Bitmap thumb = BitmapFactory.decodeResource(myContext.getResources(), images[position], options);

我猜你的上下文由于某种原因是空的，因为它是你从构造函数中获得的唯一引用，而不是你自己创建的。尝试使用 getApplicationContext().getResources()。

于 2013-06-21T07:12:25.727 回答
0

在 getView 中，使用 myContext 代替活动。尝试，

 if(itemView == null) {
    inflater = (LayoutInflater)myContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    itemView  = inflater.inflate(R.layout.item_view, null);         

}


imgView = (ImageView)itemView.findViewById(R.id.img_item);
         textView = (TextView)itemView.findViewById(R.id.text_item);
         textView.setText("Hello");
于 2013-06-21T07:19:21.143 回答