我必须修复一个错误 nullpointerexception

Posted 2023-02-19

【中文标题】我必须修复一个错误 nullpointerexception

【英文标题】：I have to fix a bug nullpointerexception

【发布时间】：2013-01-31 18:43:30

【问题描述】：

我有一个仅出现在 froyo 设备中的错误

Bitmap.createScaledBitmap() 中的空指针异常

java.lang.RuntimeException: An error occured while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:200)
at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274)
at java.util.concurrent.FutureTask.setException(FutureTask.java:125)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581)
at java.lang.Thread.run(Thread.java:1019)
Caused by: java.lang.NullPointerException
at android.graphics.Bitmap.createScaledBitmap(Bitmap.java:344)
at com.varxstudio.beautifulwallpapersLite.Imagen.a(Unknown Source)
at com.varxstudio.beautifulwallpapersLite.g.a(Unknown Source)
at com.varxstudio.beautifulwallpapersLite.g.doInBackground(Unknown Source)
at android.os.AsyncTask$2.call(AsyncTask.java:185)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306)

这里的代码有什么解决方案吗？为什么只在froyo？？？ 以前只使用 BitmapFactory.decodeStream(inputStream) 来加载图像，但我找到了一个flusedInputStream方法来做到这一点，但我仍然得到同样的错误

private class DownloadDialog extends AsyncTask<Void, Void, Void> 

    ProgressDialog myDialog = null;
    int result = 0;

    @Override
    protected void onPreExecute() 
        myDialog = ProgressDialog.show(Imagen.this, "", advert);
        myDialog.setCancelable(true);
        return;
    

    @Override
    protected Void doInBackground(Void... params) 
        result = setWallpaper(path);

        return null;
    

    @Override
    protected void onPostExecute(Void result) 
        myDialog.dismiss();
        switch (result)
            ----
        
        return;
    


public int setWallpaper(String path)           
    int width, height;
    Bitmap dbm, bm;         
    bm = null;
    dbm = null; 
    InputStream is = null;

    WallpaperManager wpm = WallpaperManager.getInstance(this);
    dis = getWindowManager().getDefaultDisplay();           

    if((wpm != null) && (dis != null)) 
        height = dis.getHeight();
        width = (int) (height * 1.33);              

        try            
            URLConnection conn = new URL(path).openConnection();                
            conn.connect();             
            is = conn.getInputStream();             

            if (is != null)                    
                bm = BitmapFactory.decodeStream(new FlushedInputStream(is));                    
                dbm = Bitmap.createScaledBitmap(bm, width, height, false);
                wpm.setBitmap(dbm);                 
            else 
                return 2;
            

         catch (MalformedURLException e)                  
            e.printStackTrace();                
         catch (IOException e)                
            e.printStackTrace();                
         finally              
            if (is != null) 
                try 
                    is.close();
                
                catch (IOException e) 
                    e.printStackTrace();
                
            
                   
        if(bm != null)
            bm.recycle();
        
        if(dbm != null)
            dbm.recycle();  
                   
    else 
        return 1;
    
    return 0;


static class FlushedInputStream extends FilterInputStream 
    public FlushedInputStream(InputStream inputStream) 
        super(inputStream);
    

    @Override
    public long skip(long n) throws IOException 
        long totalBytesSkipped = 0L;
        while (totalBytesSkipped < n) 
            long bytesSkipped = in.skip(n - totalBytesSkipped);
            if (bytesSkipped == 0L) 
                int b = read();
                if (b < 0) 
                    break;  // we reached EOF
                 else 
                    bytesSkipped = 1; // we read one byte
                
            
            totalBytesSkipped += bytesSkipped;
        
        return totalBytesSkipped;
    

【问题讨论】：

bm 是否为空？如果无法处理图像，decodeStream 返回 null。

【参考方案1】：

你有 NullPointerException 因为 BitmapFactory.decodeStream(new FlushedInputStream(is)); 返回 null，BitmapFactory.decodeStream(stream) 返回 null 的原因是因为图像不好.. 从某种意义上说，坏图像确保您返回的是 Android 支持的位图格式（例如 Android doesn't support tiff）。第二个原因是因为图像分辨率，如果图像分辨率太高解码失败..所以确保你有小图像。

这是我在 SO 中发布的关于同一问题的问题..Bitmap failed to create using BitmapFactory.decodeArray

我之前也遇到过同样的问题，但是我通过使用Android开发者网站Displaying Bitmaps Efficiently提供的教程解决了这个问题