我已经注意到android.support.v4.widget.CircleImageView很久了。每当我想要使用圆形的ImageView时，CircleImageView就会出现在我的脑海中。我试过多次使用它，但每次都失败了。由于android.support.v4.widget.CircleImageView的访问权限为 默认 ，这意味着只有CircleImageView的同一个包中的类，即android.support.v4.widget，能够访问它。
我现在无法理解轮次ImageView是常用的，为什么不将CircleImageView设置为公开，以便开发人员不必将ImageView覆盖为圆形ImageView？是不是Google Android团队强迫我们重新发明轮子？
或者，我不知道这个CircleImageView吗？
任何提示将不胜感激。提前谢谢。
答案 0 :(得分：8)
我尝试复制并粘贴android.support.v4.widget.CircleImageView的源代码，使其公开，如下所示：
package me.danielpan.youtubelike.view;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.RadialGradient;
import android.graphics.Shader;
import android.graphics.drawable.ShapeDrawable;
import android.graphics.drawable.shapes.OvalShape;
import android.support.v4.view.ViewCompat;
import android.view.animation.Animation;
import android.widget.ImageView;
/**
* Private class created to work around issues with AnimationListeners being
* called before the animation is actually complete and support shadows on older
* platforms.
*
* @hide
*/
public class CircleImageView extends ImageView {
private static final int KEY_SHADOW_COLOR = 0x1E000000;
private static final int FILL_SHADOW_COLOR = 0x3D000000;
// PX
private static final float X_OFFSET = 0f;
private static final float Y_OFFSET = 1.75f;
private static final float SHADOW_RADIUS = 3.5f;
private static final int SHADOW_ELEVATION = 4;
private Animation.AnimationListener mListener;
private int mShadowRadius;
public CircleImageView(Context context, int color, final float radius) {
super(context);
final float density = getContext().getResources().getDisplayMetrics().density;
final int diameter = (int) (radius * density * 2);
final int shadowYOffset = (int) (density * Y_OFFSET);
final int shadowXOffset = (int) (density * X_OFFSET);
mShadowRadius = (int) (density * SHADOW_RADIUS);
ShapeDrawable circle;
if (elevationSupported()) {
circle = new ShapeDrawable(new OvalShape());
ViewCompat.setElevation(this, SHADOW_ELEVATION * density);
} else {
OvalShape oval = new OvalShadow(mShadowRadius, diameter);
circle = new ShapeDrawable(oval);
ViewCompat.setLayerType(this, ViewCompat.LAYER_TYPE_SOFTWARE, circle.getPaint());
circle.getPaint().setShadowLayer(mShadowRadius, shadowXOffset, shadowYOffset,
KEY_SHADOW_COLOR);
final int padding = mShadowRadius;
// set padding so the inner image sits correctly within the shadow.
setPadding(padding, padding, padding, padding);
}
circle.getPaint().setColor(color);
setBackgroundDrawable(circle);
}
private boolean elevationSupported() {
return android.os.Build.VERSION.SDK_INT >= 21;
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
if (!elevationSupported()) {
setMeasuredDimension(getMeasuredWidth() + mShadowRadius*2, getMeasuredHeight()
+ mShadowRadius*2);
}
}
public void setAnimationListener(Animation.AnimationListener listener) {
mListener = listener;
}
@Override
public void onAnimationStart() {
super.onAnimationStart();
if (mListener != null) {
mListener.onAnimationStart(getAnimation());
}
}
@Override
public void onAnimationEnd() {
super.onAnimationEnd();
if (mListener != null) {
mListener.onAnimationEnd(getAnimation());
}
}
/**
* Update the background color of the circle image view.
*
* @param colorRes Id of a color resource.
*/
public void setBackgroundColorRes(int colorRes) {
setBackgroundColor(getContext().getResources().getColor(colorRes));
}
@Override
public void setBackgroundColor(int color) {
if (getBackground() instanceof ShapeDrawable) {
((ShapeDrawable) getBackground()).getPaint().setColor(color);
}
}
private class OvalShadow extends OvalShape {
private RadialGradient mRadialGradient;
private Paint mShadowPaint;
private int mCircleDiameter;
public OvalShadow(int shadowRadius, int circleDiameter) {
super();
mShadowPaint = new Paint();
mShadowRadius = shadowRadius;
mCircleDiameter = circleDiameter;
mRadialGradient = new RadialGradient(mCircleDiameter / 2, mCircleDiameter / 2,
mShadowRadius, new int[] {
FILL_SHADOW_COLOR, Color.TRANSPARENT
}, null, Shader.TileMode.CLAMP);
mShadowPaint.setShader(mRadialGradient);
}
@Override
public void draw(Canvas canvas, Paint paint) {
final int viewWidth = CircleImageView.this.getWidth();
final int viewHeight = CircleImageView.this.getHeight();
canvas.drawCircle(viewWidth / 2, viewHeight / 2, (mCircleDiameter / 2 + mShadowRadius),
mShadowPaint);
canvas.drawCircle(viewWidth / 2, viewHeight / 2, (mCircleDiameter / 2), paint);
}
}
}
看起来不错吧？它没有自定义属性，似乎可以用作普通ImageView。
但是如果你已经尝试过，你会发现NoSuchMethodException被抛出。此异常意味着不会覆盖必要的构造函数。因此，您甚至无法将其实例化为普通View。
在阅读完这些源代码后，我发现CircleImageView只会在ImageView后面添加阴影，其结果不是RoundCornerImageView或RoundImageView。因此，如果我想要RoundImageView，我必须忘记这个类并通过覆盖ImageView来实现此效果。
最后，有文件评论，指出使用android.support.v4.widget.CircleImageView：
为解决AnimationListeners问题而创建的私有类 在动画实际完成和支持之前被调用 旧平台上的阴影。
我希望没有人再问这样一个愚蠢的问题，让它在这里结束，^ _ ^，哈哈〜
答案 1 :(得分：3)
根据文档，这个类是用于解决的私有类，我们无法实例化它。可能是我怀疑的那个课程将被删除。
有一些方法可以为视图创建圆形背景。
file：drawable / contact_badge_round.xml
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape="oval">
<size android:width="32dp" android:height="32dp"/>
<gradient android:centerColor="#123456" <!--Put your custom color for bg -->
android:startColor="#123456"
android:endColor="#123456"
/>
</shape>
然后在你的布局中创建一个Button并将背景设置为contact_badge_round
<ImageView
android:id="@+id/roundContact"
android:layout_width="32dp"
android:layout_height="32dp"
android:src="@drawalbe/your_image"
android:gravity="center"
android:background="@drawable/background_new_entity_symbol"
/>