Android bitmap 一些常用用法

说到Bitmap，Android 的朋友肯定很熟悉了，下面是我对bitmap一些常用方法的总结。之后会陆续更新。

圆角bitmap

/**
*
* @param source
* @param radius 圆角半径
* @return
*/

public static Bitmap getRoundCornerBitmap(Bitmap source, float radius) {
if (source == null) return null;
if(radius <= 0){
return source;
}
Bitmap result = Bitmap.createBitmap(source.getWidth(), source.getHeight(), Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(result);
Paint paint = new Paint();
paint.setShader(new BitmapShader(source, BitmapShader.TileMode.CLAMP, BitmapShader.TileMode.CLAMP));
paint.setAntiAlias(true);
RectF rectF = new RectF(0f, 0f, source.getWidth(), source.getHeight());
canvas.drawRoundRect(rectF, radius, radius, paint);
return result;
}

读取Asset图片

public static Bitmap getImageFromAssetsFile(String fileName, Context context){
Bitmap image = null;
AssetManager am = context.getResources().getAssets();
InputStream is = null;
try {
is = am.open(fileName);
image = BitmapFactory.decodeStream(is);
is.close();
}catch (IOException e) {
e.printStackTrace();
}finally {
if (is != null){
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
return image;
}

缩放图片

public static Bitmap scaleBitmap(Bitmap bitmap, int dstWidth, int dstHeight) {
if(bitmap == null){
return null;
}
int width = bitmap.getWidth();
int height = bitmap.getHeight();
float scaleWidth = ((float) dstWidth) / width;
float scaleHeight = ((float) dstHeight) / height;
Matrix matrix = new Matrix();
matrix.postScale(scaleWidth, scaleHeight);
Bitmap newbm = Bitmap.createBitmap(bitmap, 0, 0, width, height, matrix, true);
return newbm;
}

读取图片

sampleSize 是指采样率，比如读取原图，sample为1，比如你要读取的图片宽高是原图的1/2，则sampleSize=2,合理使用sampleSize能有效节省内存，比如原图宽高为1080x1920, 而实际只需要显示在108x192的imageview上，最暴力的方法，直接读取原图，但这样很容易oom，或者读取原图，然后放缩到指定尺寸，这个过程也会消耗大量内存，而按照下面的方法，只需要设置sampleSize=10就可以了。

public static Bitmap getBitmapWithPath(String path, int sampleSize){
if(TextUtils.isEmpty(path)){
return null;
}
if(sampleSize <= 0){
sampleSize = 1;

b221
}
File file = new File(path);
if(file.exists() && file.isFile()) {
BitmapFactory.Options boundOptions = new BitmapFactory.Options();
boundOptions.inJustDecodeBounds = false;
boundOptions.inSampleSize = sampleSize;
boundOptions.inDither = true;
boundOptions.inPreferredConfig = Bitmap.Config.ARGB_8888;
return BitmapFactory.decodeFile(path, boundOptions);
}
return null;
}

所以读取一个图片的时候最好的流程这样：读取图片大小（见下述代码）–>计算缩放比例–>读取指定大小的图片（见上述代码）

读取图片大小

public static Size getBitmapBoundWithPath(String path){
InputStream input = null;
try {
input = new FileInputStream(path);
if(input == null){
return null;
}
BitmapFactory.Options boundOptions = new BitmapFactory.Options();
boundOptions.inJustDecodeBounds = true;
boundOptions.inSampleSize = 1;
BitmapFactory.decodeStream(input, null, boundOptions);//只取宽高，节省内存
input.close();
return new Size(boundOptions.outWidth, boundOptions.outHeight);
} catch (Exception e) {
Log.d(TAG, "exception:" + e.getMessage());
return null;
}finally {
if(input != null){
try {
input.close();
} catch (IOException e) {
Log.d(TAG, "exception:" + e.getMessage());
return null;
}
}
}
}

从视频中获取帧

下面的代码并不能兼容所有的Android机器，比如华为P10用下面方法截帧是不靠谱的。

/**
*
* @param path
* @param time 毫秒
* @return
*/
public static Bitmap getFrameFromVideo(String path, long time){
try {
MediaMetadataRetriever retriever = new MediaMetadataRetriever();
retriever.setDataSource(path);
String durationStr = retriever.extractMetadata(MediaMetadataRetriever.METADATA_KEY_DURATION);
long duration = Integer.valueOf(durationStr);
if(time > duration || time < 0){
return null;
}
Bitmap bitmap = retriever.getFrameAtTime(time * 1000);
return bitmap;
}catch (Exception e){
return null;
}
}