使用Bitmap.createBitmap遇到的問題
阿新 • • 發佈:2019-01-30
Bitmap.java中createBitmap函式呼叫的是以下重構方法
public static Bitmap createBitmap(Bitmap source, int x, int y, int width, int height, Matrix m, boolean filter) { checkXYSign(x, y); checkWidthHeight(width, height); if (x + width > source.getWidth()) { throw new IllegalArgumentException("x + width must be <= bitmap.width()"); } if (y + height > source.getHeight()) { throw new IllegalArgumentException("y + height must be <= bitmap.height()"); } // check if we can just return our argument unchanged if (!source.isMutable() && x == 0 && y == 0 && width == source.getWidth() && height == source.getHeight() && (m == null || m.isIdentity())) { return source; } int neww = width; int newh = height; Canvas canvas = new Canvas(); Bitmap bitmap; Paint paint; Rect srcR = new Rect(x, y, x + width, y + height); RectF dstR = new RectF(0, 0, width, height); Config newConfig = Config.ARGB_8888; final Config config = source.getConfig(); // GIF files generate null configs, assume ARGB_8888 if (config != null) { switch (config) { case RGB_565: newConfig = Config.RGB_565; break; case ALPHA_8: newConfig = Config.ALPHA_8; break; //noinspection deprecation case ARGB_4444: case ARGB_8888: default: newConfig = Config.ARGB_8888; break; } } if (m == null || m.isIdentity()) { bitmap = createBitmap(neww, newh, newConfig, source.hasAlpha()); paint = null; // not needed } else { final boolean transformed = !m.rectStaysRect(); RectF deviceR = new RectF(); m.mapRect(deviceR, dstR); neww = Math.round(deviceR.width()); newh = Math.round(deviceR.height()); bitmap = createBitmap(neww, newh, transformed ? Config.ARGB_8888 : newConfig, transformed || source.hasAlpha()); canvas.translate(-deviceR.left, -deviceR.top); canvas.concat(m); paint = new Paint(); paint.setFilterBitmap(filter); if (transformed) { paint.setAntiAlias(true); } } // The new bitmap was created from a known bitmap source so assume that // they use the same density bitmap.mDensity = source.mDensity; canvas.setBitmap(bitmap); canvas.drawBitmap(source, srcR, dstR, paint); canvas.setBitmap(null); return bitmap; }
注意發現其中有以下程式碼
// check if we can just return our argument unchanged
if (!source.isMutable() && x == 0 && y == 0 && width == source.getWidth() &&
height == source.getHeight() && (m == null || m.isIdentity())) {
return source;
}
以上程式碼的邏輯是:如果源點陣圖是 immutable且請求返回的點陣圖是和源點陣圖一樣的,則直接返回源點陣圖,並不建立新點陣圖。所以你在使用它的時候很可能會返回一個你之前傳進來的bitmap。所以如果你把認為是臨時變數的bitmap回收掉之後,其實是把不該回收的也回收了。這時就會丟擲詭異的bitmap回收問題,說是使用了recycled的bitmap。如果一定需要建立一個拷貝的話,可以嘗試使用Bitmap.copy(Config
config, boolean isMutable)方法代替。