In-depth understanding of the technical principles of the CircleImageView framework in the Java class library
In -depth understanding of the technical principles of the CircleImageView framework in the Java class library
Brief introduction
CircleImageView is a commonly used Java class library framework that is used to display round pictures in Android applications.By cutting square pictures into a circular shape and displaying it in the ImageView control, the CircleImageView framework provides a simple and elegant way to display circular pictures.This article will deeply understand the technical principles of the CircleImageView framework and provide relevant Java code examples.
Technical principle
1. Drawable and bitmap
Before understanding the CircleImageView framework, you must first understand the two concepts of Drawable and Bitmap.Drawable is an abstract concept that represents a drawable object that can contain pictures, colors and graphics.Bitmap is a specific implementation that represents a bitmap object that is used in Android to represent a picture.
2. Image cutting
One of the core technical principles of the CircleImageView framework is picture cutting.To display a round picture, we need to cut the square Bitmap object into a circular shape.A common method is to create a round shear path by creating a Bitmap object with the same size as the original picture, and then use Canvas to draw a round shear path.Finally, we apply the original picture and shear path to this bitmap object to get a circular Bitmap.
The following is an example of using Java code to implement picture cutting:
public Bitmap cropToCircle(Bitmap bitmap) {
Bitmap output = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(), Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(output);
final int color = 0xff424242;
final Paint paint = new Paint();
final Rect rect = new Rect(0, 0, bitmap.getWidth(), bitmap.getHeight());
final RectF rectF = new RectF(rect);
final float roundPx = bitmap.getWidth() / 2;
paint.setAntiAlias(true);
canvas.drawARGB(0, 0, 0, 0);
paint.setColor(color);
canvas.drawRoundRect(rectF, roundPx, roundPx, paint);
paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
canvas.drawBitmap(bitmap, rect, rect, paint);
return output;
}
3. Custom ImageView
Another key technical principle of the CircleImageView framework is customized ImageView.To display the round pictures after cutting, we need to use a custom ImageView control.In this custom control, we cut the picture before drawing a picture, and display the tailored circular pictures.
The following is an example of customization of ImageView using Java code:
public class CircleImageView extends AppCompatImageView {
private Bitmap croppedBitmap;
public CircleImageView(Context context) {
super(context);
}
public CircleImageView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public CircleImageView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
protected void onDraw(Canvas canvas) {
if (croppedBitmap != null) {
canvas.drawBitmap(croppedBitmap, 0, 0, null);
}
}
@Override
public void setImageBitmap(Bitmap bm) {
croppedBitmap = cropToCircle(bm);
super.setImageBitmap(croppedBitmap);
}
private Bitmap cropToCircle(Bitmap bitmap) {
// Image cutting logic
// ...
return croppedBitmap;
}
}
In the custom CircleImageView, we rewritten the ONDRAW method, using Canvas to draw a round picture after cutting.In the SetImageBitMap method, we called the Croptocircle method to cut the inlet Bitmap objects, and set the croppedBitmap property based on the cut round picture after cutting.
Summarize
By deeply understanding the technical principles of the CircleImageView framework, we have learned that it mainly implements the two key technical principles of cropping and customization of ImageView.By cutting square pictures and drawing a circular cutting path, the CircleImageView framework can show an elegant and beautiful circular picture effect.We also understand the specific implementation methods of this framework by providing the Java code example.I hope this article will help understand the technical principles of understanding the CircleImageView framework.
