Java 为什么 BitmapFactory.decodeByteArray 返回 null？
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Why does BitmapFactory.decodeByteArray return null?
提问by sandalone
It's the simple code and instead of getting result to set the Bitmap, I get null. Can anyone tell me where I am making a mistake?
这是简单的代码，而不是获得设置位图的结果，我得到了空值。谁能告诉我我在哪里犯了错误？
String test = "test";
byte[] byteA = test.getBytes();
Bitmap bmp = BitmapFactory.decodeByteArray(byteA, 0, byteA.length); //<- I get null here
ImageView image = (ImageView) findViewById(R.id.image);
image.setImageBitmap(bmp);
UPDATE
更新
Ok, so I cannot convert text to image like I thought I could. How about this way? Will this create a bitmap?
好的，所以我无法像我想的那样将文本转换为图像。这条路怎么样？这会创建位图吗？
Paint paint = new Paint();
paint.setStyle(Paint.Style.FILL);
paint.setColor(Color.RED);
paint.setTextSize(16);
paint.setAntiAlias(true);
paint.setTypeface(Typeface.MONOSPACE);
Bitmap bm = Bitmap.createBitmap(16, 16, Bitmap.Config.ALPHA_8);
float x = bm.getWidth();
float y = bm.getHeight();
Canvas c = new Canvas(bm);
c.drawText("Test", x, y, paint);
采纳答案by Jon Skeet
From the documentation:
从文档：
ReturnsThe decoded bitmap, or null if the image could not be decode.
返回解码后的位图，如果图像无法解码，则返回null。
The bytes involved in the string "test" aren't a valid bitmap, are they?
字符串“test”中涉及的字节不是有效的位图，是吗？
If you saved the text "test" in a file called foo.pngor foo.jpgetc and tried to open it in Windows, what would you expect the result to be? It would be an error: those bytes simply aren'ta valid image in any known format.
如果您将文本“test”保存在名为foo.pngor foo.jpgetc的文件中并尝试在 Windows 中打开它，您希望结果是什么？这将是一个错误：这些字节根本不是任何已知格式的有效图像。
EDIT: I don't know anything about Android graphics, but your update certainly lookslike a much more reasonable way to draw text onto a bitmap.
编辑：我对 Android 图形一无所知，但您的更新看起来确实是在位图上绘制文本的更合理的方式。
回答by aioobe
Because the bytes in "test".getBytes()doesn't represent a valid bitmap.
因为中的字节"test".getBytes()不代表有效的位图。
You need to create a byte-array which actually contains an encoded bitmap, not just some "random bytes" corresponding to the representation of a string.
您需要创建一个字节数组，它实际上包含一个编码位图，而不仅仅是一些与字符串表示相对应的“随机字节”。
回答by inazaruk
You get nullbecause you supply invalid bitmap data.
你得到null是因为你提供了无效的位图数据。
See documentation of BitmapFactory.decodeByteArray().
回答by Mark Allison
You're trying to parse a String as a bitmap. BitmapFactory.decodeByteArray()will fail unless there is a valid bitmap in the byte array. In this case there isn't, so it returns null.
您正在尝试将 String 解析为位图。BitmapFactory.decodeByteArray()除非字节数组中存在有效位图，否则将失败。在这种情况下没有，所以它返回 null。
回答by Mustafa Güven
In such case you need to convert the string to Base64 first.
在这种情况下，您需要先将字符串转换为 Base64。
String strImage = geTImageAsHexString();
byte[] x = Base64.decode(strImage, Base64.DEFAULT); //convert from base64 to byte array
Bitmap bmp = BitmapFactory.decodeByteArray(x,0,x.length);
回答by Vlad
byte array of compressed image data - what is this and how it is different from byte[] data = new byte[sz]?
压缩图像数据的字节数组 - 这是什么以及它与 byte[] data = new byte[sz] 有何不同？
Nobody so far gave clear answer! All that people been talking about is that there is an invalid Bitmap. A more informative answer would be how to create a valid byte array on the low level
至今没有人给出明确的答案！人们一直在谈论的是有一个无效的位图。一个更有用的答案是如何在低级别创建一个有效的字节数组
回答by Jevgenij Kononov
In my case BitmapFactory.decodeByteArray returned null because received image buffer was incorrect. Try to see sending buffer and incoming buffer, I am sure you will see the difference in two arrays. Most of the time this is the cause.
在我的情况下 BitmapFactory.decodeByteArray 返回 null 因为接收到的图像缓冲区不正确。尝试查看发送缓冲区和传入缓冲区，我相信您会看到两个数组的区别。大多数时候这是原因。
