Android 将图像从ImageView转换为Base64字符串

我正在尝试使用下面的代码将图像从

IMAGEVIEW

转换为Base64字符串，但这会导致

NullPointerException

代码如下：

ImageView iv1 = (ImageView)findViewById(R.id.imageView1);
iv1.buildDrawingCache();
Bitmap bmap = iv1.getDrawingCache();
ByteArrayOutputStream bos = new ByteArrayOutputStream();  
bmap.compress(CompressFormat.PNG,100,bos); 
byte[] bb = bos.toByteArray();
String image = Base64.encodeBytes(bb);

下面是logcat所说的：

04-30 11:38:23.233: E/AndroidRuntime(17284): FATAL EXCEPTION: main
04-30 11:38:23.233: E/AndroidRuntime(17284): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.imageurl/com.example.imageurl.MainActivity}: java.lang.NullPointerException
04-30 11:38:23.233: E/AndroidRuntime(17284):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
04-30 11:38:23.233: E/AndroidRuntime(17284):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
04-30 11:38:23.233: E/AndroidRuntime(17284):    at android.app.ActivityThread.access$600(ActivityThread.java:130)
04-30 11:38:23.233: E/AndroidRuntime(17284):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
04-30 11:38:23.233: E/AndroidRuntime(17284):    at android.os.Handler.dispatchMessage(Handler.java:99)
04-30 11:38:23.233: E/AndroidRuntime(17284):    at android.os.Looper.loop(Looper.java:137)
04-30 11:38:23.233: E/AndroidRuntime(17284):    at android.app.ActivityThread.main(ActivityThread.java:4745)
04-30 11:38:23.233: E/AndroidRuntime(17284):    at java.lang.reflect.Method.invokeNative(Native Method)
04-30 11:38:23.233: E/AndroidRuntime(17284):    at java.lang.reflect.Method.invoke(Method.java:511)
04-30 11:38:23.233: E/AndroidRuntime(17284):    at  com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
04-30 11:38:23.233: E/AndroidRuntime(17284):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
04-30 11:38:23.233: E/AndroidRuntime(17284):    at dalvik.system.NativeStart.main(Native Method)
 04-30 11:38:23.233: E/AndroidRuntime(17284): Caused by: java.lang.NullPointerException
 04-30 11:38:23.233: E/AndroidRuntime(17284):   at com.example.imageurl.MainActivity.onCreate(MainActivity.java:59)
 04-30 11:38:23.233: E/AndroidRuntime(17284):   at android.app.Activity.performCreate(Activity.java:5008)
 04-30 11:38:23.233: E/AndroidRuntime(17284):   at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
 04-30 11:38:23.233: E/AndroidRuntime(17284):   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)

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我已经修好了。NullPointerException是由此行引起的

iv1.buildDrawingCache();
Bitmap bmap = iv1.getDrawingCache();

因此，我没有使用上面的代码，而是使用下面的代码

BitmapDrawable drawable = (BitmapDrawable) iv.getDrawable();
Bitmap bitmap = drawable.getBitmap();

---

检查此项，它也在工作：

iv1.buildDrawingCache();
Bitmap bitmap = iv1.getDrawingCache();

ByteArrayOutputStream stream=new ByteArrayOutputStream();
bitmap.compress(Bitmap.CompressFormat.PNG, 90, stream);
byte[] image=stream.toByteArray();
System.out.println("byte array:"+image);

String img_str = Base64.encodeToString(image, 0);
System.out.println("string:"+img_str);

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行MainActivity.java:59中的代码是什么？如果您已经解决了问题，请将您的答案标记为正确，然后关闭问题。