Exploring the technical principles of the CircleImageView framework in the Java library
In the Java library, a framework named CircleImageView is widely used to achieve a circular image display.This article will explore the technical principles of the CircleImageView framework and provide the Java code example for readers in need.
The CircleImageView framework shows round images by customized drawing on the basis of ImageView.Unlike ordinary ImageView, CircleImageView has customized drawing logic to achieve circular effects.The technical principles of the CircleImageView framework will be explained in detail below.
The main principle of CircleImageView is to use BitmapShader and Canvas objects to draw round images.First, the framework converts the image provided by the user to the Bitmap object and uses the Bitmap object as the background of the canvas.Then use BitmapShader to set the drawing area of the canvas to a round, and draw a circular image.In the end, the drawing results are displayed on ImageView.This method can make images displayed images a circular effect.
The following is a simple Java code example, which shows how to use the CircleImageView framework to display a circular image in Android applications:
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapShader;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Shader;
import android.util.AttributeSet;
import androidx.appcompat.widget.AppCompatImageView;
public class CircleImageView extends AppCompatImageView {
private Paint paint;
private Bitmap bitmap;
private BitmapShader bitmapShader;
public CircleImageView(Context context) {
super(context);
init();
}
public CircleImageView(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
public CircleImageView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init();
}
private void init() {
paint = new Paint();
paint.setAntiAlias(true);
}
@Override
protected void onDraw(Canvas canvas) {
if (bitmapShader != null) {
canvas.drawCircle(getWidth() / 2, getHeight() / 2, getWidth() / 2, paint);
}
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
if (bitmap != null) {
bitmap = Bitmap.createScaledBitmap(bitmap, w, h, false);
bitmapShader = new BitmapShader(bitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);
paint.setShader(bitmapShader);
}
}
public void setImageBitmap(Bitmap bitmap) {
super.setImageBitmap(bitmap);
this.bitmap = bitmap;
}
}
The CircleImageView class in the above code inherits from AppCompatimageView, which is a subclass of ImageView.In the ONDRAW method, the DrawCircle method of Canvas object is used to draw a circular area.In the ONSIZECHANGED method, the Bitmap object provided by the user is zoomed in, and a BitmapShader object is created as a shadeer as a paint.Finally, set up pictures and update the canvas in the SetImageBitMap method.
By using the CircleImageView framework, developers can easily achieve circular images display in Android applications.The technical principles of this framework are mainly achieved through BitmapShader and Canvas objects. Developers can customize and expand them customized according to their needs.It is hoped that this article can help readers understand the technical principles of the CircleImageView framework.
