关于使用Glide加载图片你需要知道的

前言：其实这个bug我1月份就遇到了，当时康师傅用的是毕加索，我用的是Glide，然后就报了个空指针异常了，今天群里又有同学在说这个bug，那我就给大家提供一下解决方案吧~

使用Glide加载图片的时候需要注意，因为Glide加载图片时是异步加载的。所以在后面直接调用ImageView对象的getDrawable()方法可能会出现空指针异常。

log如下：

    --------- beginning of crash
2020-06-11 20:23:07.806 27136-27136/com.smart.himalaya E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.smart.himalaya, PID: 27136
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.smart.himalaya/com.smart.himalaya.DetailActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.graphics.Bitmap android.graphics.drawable.BitmapDrawable.getBitmap()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3270)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.graphics.Bitmap android.graphics.drawable.BitmapDrawable.getBitmap()' on a null object reference
        at com.smart.himalaya.utils.ImageBlur.makeBlur(ImageBlur.java:15)
        at com.smart.himalaya.DetailActivity.onAlbumLoaded(DetailActivity.java:298)
        at com.smart.himalaya.presenters.AlbumDetailPresenter.registerViewCallback(AlbumDetailPresenter.java:133)
        at com.smart.himalaya.DetailActivity.initPresenter(DetailActivity.java:104)
        at com.smart.himalaya.DetailActivity.onCreate(DetailActivity.java:83)
        at android.app.Activity.performCreate(Activity.java:7802)
        at android.app.Activity.performCreate(Activity.java:7791)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) 
        at android.os.Handler.dispatchMessage(Handler.java:107) 
        at android.os.Looper.loop(Looper.java:214) 
        at android.app.ActivityThread.main(ActivityThread.java:7356) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) 

解决办法如下：

1. 使用Handler延时处理（处理之前还是得先判空才行）
2. 使用Glide的图片加载监听器（推荐）

方法一：使用Handler：

方法二：使用Glide的监听器：

我们还需要改造一下ImageBlur工具类（用到了一个将Drawable对象转换成Bitmap对象的工具类）：

ImageBlur.java

public class ImageBlur {
    public static void makeBlur(Context context, ImageView imageview) {
        BitmapDrawable drawable = (BitmapDrawable) imageview.getDrawable();
        Bitmap bitmap = drawable.getBitmap();
        Bitmap blurred = blurRenderScript(bitmap, 10, context); //second parametre is radius max:25
        imageview.setImageBitmap(blurred); //radius decide blur amount
    }

    public static void makeBlur(Context context, Drawable drawable, ImageView imageView) {
        Bitmap bitmap = ImageTools.drawableToBitmap(drawable);
        Bitmap blurred = blurRenderScript(bitmap, 10, context); //second parametre is radius max:25
        imageView.setImageBitmap(blurred); //radius decide blur amount
    }

    public static void makeBlur(Context context, Bitmap bitmap, ImageView imageview) {
        Bitmap blurred = blurRenderScript(bitmap, 10, context); //second parametre is radius max:25
        imageview.setImageBitmap(blurred); //radius decide blur amount
    }

    private static Bitmap blurRenderScript(Bitmap smallBitmap, int radius, Context context) {
        smallBitmap = RGB565toARGB888(smallBitmap);
        Bitmap bitmap = Bitmap.createBitmap(smallBitmap.getWidth(), smallBitmap.getHeight(), Bitmap.Config.ARGB_8888);
        RenderScript renderScript = RenderScript.create(context);
        Allocation blurInput = Allocation.createFromBitmap(renderScript, smallBitmap);
        Allocation blurOutput = Allocation.createFromBitmap(renderScript, bitmap);
        ScriptIntrinsicBlur blur = ScriptIntrinsicBlur.create(renderScript, Element.U8_4(renderScript));
        blur.setInput(blurInput);
        blur.setRadius(radius); // radius must be 0 < r <= 25
        blur.forEach(blurOutput);
        blurOutput.copyTo(bitmap);
        renderScript.destroy();
        return bitmap;
    }

    private static Bitmap RGB565toARGB888(Bitmap img) {
        int numPixels = img.getWidth() * img.getHeight();
        int[] pixels = new int[numPixels];

        //Get JPEG pixels.  Each int is the color values for one pixel.
        img.getPixels(pixels, 0, img.getWidth(), 0, 0, img.getWidth(), img.getHeight());

        //Create a Bitmap of the appropriate format.
        Bitmap result = Bitmap.createBitmap(img.getWidth(), img.getHeight(), Bitmap.Config.ARGB_8888);

        //Set RGB pixels.
        result.setPixels(pixels, 0, result.getWidth(), 0, 0, result.getWidth(), result.getHeight());
        return result;
    }
}

ImageTools.java

/**
 * Tools for handler picture
 *
 * @author Ryan.Tang
 */
public final class ImageTools {

    /**
     * Transfer drawable to bitmap 把drawable转换为bitmap
     *
     * @param drawable
     * @return
     */
    public static Bitmap drawableToBitmap(Drawable drawable) {
        int w = drawable.getIntrinsicWidth();
        int h = drawable.getIntrinsicHeight();

        Config config = drawable.getOpacity() != PixelFormat.OPAQUE ? Config.ARGB_8888
                : Config.RGB_565;
        Bitmap bitmap = Bitmap.createBitmap(w, h, config);
        Canvas canvas = new Canvas(bitmap);
        drawable.setBounds(0, 0, w, h);
        drawable.draw(canvas);
        return bitmap;
    }

    /**
     * Bitmap to drawable
     *
     * @param bitmap
     * @return
     */
    public static Drawable bitmapToDrawable(Bitmap bitmap) {
        return new BitmapDrawable(bitmap);
    }

    /**
     * Input stream to bitmap
     *
     * @param inputStream
     * @return
     * @throws Exception
     */
    public static Bitmap inputStreamToBitmap(InputStream inputStream)
            throws Exception {
        return BitmapFactory.decodeStream(inputStream);
    }

    /**
     * Byte transfer to bitmap
     *
     * @param byteArray
     * @return
     */
    public static Bitmap byteToBitmap(byte[] byteArray) {
        if (byteArray.length != 0) {
            return BitmapFactory
                    .decodeByteArray(byteArray, 0, byteArray.length);
        } else {
            return null;
        }
    }

    /**
     * Byte transfer to drawable
     *
     * @param byteArray
     * @return
     */
    public static Drawable byteToDrawable(byte[] byteArray) {
        ByteArrayInputStream ins = null;
        if (byteArray != null) {
            ins = new ByteArrayInputStream(byteArray);
        }
        return Drawable.createFromStream(ins, null);
    }

    /**
     * Bitmap transfer to bytes
     *
     * @return
     */
    public static byte[] bitmapToBytes(Bitmap bm) {
        byte[] bytes = null;
        if (bm != null) {
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            bm.compress(Bitmap.CompressFormat.PNG, 100, baos);
            bytes = baos.toByteArray();
        }
        return bytes;
    }

    /**
     * Drawable transfer to bytes
     *
     * @param drawable
     * @return
     */
    public static byte[] drawableToBytes(Drawable drawable) {
        BitmapDrawable bitmapDrawable = (BitmapDrawable) drawable;
        Bitmap bitmap = bitmapDrawable.getBitmap();
        byte[] bytes = bitmapToBytes(bitmap);
        ;
        return bytes;
    }

    /**
     * Base64 to byte[] 
     //   */
//  public static byte[] base64ToBytes(String base64) throws IOException {  
//      byte[] bytes = Base64.decode(base64);  
//      return bytes;  
//  }  
//  
//  /**  
//   * Byte[] to base64  
//   */  
//  public static String bytesTobase64(byte[] bytes) {  
//      String base64 = Base64.encode(bytes);  
//      return base64;  
//  }  

    /**
     * Create reflection images
     *
     * @param bitmap
     * @return
     */
    public static Bitmap createReflectionImageWithOrigin(Bitmap bitmap) {
        final int reflectionGap = 4;
        int w = bitmap.getWidth();
        int h = bitmap.getHeight();

        Matrix matrix = new Matrix();
        matrix.preScale(1, -1);

        Bitmap reflectionImage = Bitmap.createBitmap(bitmap, 0, h / 2, w,
                h / 2, matrix, false);

        Bitmap bitmapWithReflection = Bitmap.createBitmap(w, (h + h / 2),
                Config.ARGB_8888);

        Canvas canvas = new Canvas(bitmapWithReflection);
        canvas.drawBitmap(bitmap, 0, 0, null);
        Paint deafalutPaint = new Paint();
        canvas.drawRect(0, h, w, h + reflectionGap, deafalutPaint);

        canvas.drawBitmap(reflectionImage, 0, h + reflectionGap, null);

        Paint paint = new Paint();
        LinearGradient shader = new LinearGradient(0, bitmap.getHeight(), 0,
                bitmapWithReflection.getHeight() + reflectionGap, 0x70ffffff,
                0x00ffffff, TileMode.CLAMP);
        paint.setShader(shader);
        // Set the Transfer mode to be porter duff and destination in  
        paint.setXfermode(new PorterDuffXfermode(Mode.DST_IN));
        // Draw a rectangle using the paint with our linear gradient  
        canvas.drawRect(0, h, w, bitmapWithReflection.getHeight()
                + reflectionGap, paint);

        return bitmapWithReflection;
    }


    public static boolean copyFileUsingFileChannels(File source, File dest, boolean shouldDelete) {
        FileChannel inputChannel = null;
        FileChannel outputChannel = null;
        try {
            try {
                inputChannel = new FileInputStream(source).getChannel();
                outputChannel = new FileOutputStream(dest).getChannel();
                outputChannel.transferFrom(inputChannel, 0, inputChannel.size());
                if (shouldDelete) {
                    //如果需要删除源文件
                    if (source.exists()) {
                        source.delete();
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
                return false;
            }
        } finally {
            try {
                inputChannel.close();
                outputChannel.close();
            } catch (IOException e) {
                e.printStackTrace();
                return false;
            }
        }

        return true;
    }

    public static Bitmap decodeUriAsBitmap(Uri uri, Context context) {
        Bitmap bitmap = null;
        try {
            // 先通过getContentResolver方法获得一个ContentResolver实例，
            // 调用openInputStream(Uri)方法获得uri关联的数据流stream
            // 把上一步获得的数据流解析成为bitmap
            bitmap = BitmapFactory.decodeStream(context.getContentResolver().openInputStream(uri));
        } catch (FileNotFoundException e) {
            e.printStackTrace();
            return null;
        }
        return bitmap;
    }

}  

如果你也遇到过这个问题，那么你就可以通过这两种方式（不太建议第一种，因为你延迟的时机可能并不准确，有的图片可能在那个时间内可以加载完成，遇到大一点的图片或者网络不好时就没办法了）进行解决啦~

如果本文解决了你的问题或者你觉得有用，那就点个赞再走呗~