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我对此很陌生。现在这个简单的应用程序从网络下载图像作为可绘制图像，然后将其转换为位图（将其存储在缓存中）并在 UI 中显示。当我运行它时，它会给出NullPointerException。

代码：-

public class ImageActivity extends Activity {
    /** Called when the activity is first created. */
    private LruCache<String, Bitmap> mchache;
    ImageView imageview;
    Bitmap image;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);


                imageview=(ImageView)findViewById(R.id.img);
        Log.i("shu","HERE @ calling loadimage");
       loadimage();

    }
    public void loadimage()

    {          Log.i("shu","HERE @ inside ");

        image = (Bitmap) mchache.get("img");
        Log.i("shu","HERE @line1passed");

        if (image==null)
        {        Log.i("shu","HERE @ imahe==null");

            downloadimage();
        }
        else if (image != null)
        {        Log.i("shu","HERE @ image!= null");

        imageview.setImageBitmap(image);
        }
    }
    // converts drawable to bitmap
    public static Bitmap drawableToBitmap (Drawable drawable) {
        Log.i("shu","HERE @ drawable to bitmap");

        if (drawable instanceof BitmapDrawable) {
            return ((BitmapDrawable)drawable).getBitmap();
        }

        Bitmap bitmap = Bitmap.createBitmap(drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight(), Config.ARGB_8888);
        Canvas canvas = new Canvas(bitmap); 
        drawable.setBounds(0, 0, canvas.getWidth(), canvas.getHeight());
        drawable.draw(canvas);

        return bitmap;
    }
    public void downloadimage()
    {        Log.i("shu","HERE @ download image");

        String address="http://abd.com/absde.jpg";
        try{ 
           URL url = new URL(address);
         InputStream content = (InputStream)url.getContent();
         Drawable d = Drawable.createFromStream(content , "src"); 
         imageview.setImageDrawable(d);
         Bitmap bmap = drawableToBitmap(d);
         mchache.put("img",bmap);
        }
        catch (IOException e)
        {        Log.i("shu","HERE @ exception");
}
    }

}

现在根据logcat，问题出在这里

            image = (Bitmap) mchache.get("img");

代码黑白两个日志信息，所以任何人都可以指出是什么原因造成的。我在支持库的帮助下使用 LRUCache，因为它在 api8 中不存在。

4

1 回答 1

1

你还没有初始化 

private LruCache<String, Bitmap> mchache;

做在onCreate()

mchache = LruCache<String, Bitmap>();

前

loadimage();
于 2012-06-26T09:43:50.713 回答