一、问题在哪里？
问题来源于app开发中一个很常见的场景——用户头像要展示成圆的：
二、怎么搞？
机智的我，第一想法就是，切一张中间圆形透明、四周与底色相同、尺寸与头像相同的蒙板图片，盖在头像上不就完事了嘛，哈哈哈！
在背景纯色的前提下，这的确能简单解决问题，但是如果背景没有这么简单呢？
在这种不规则背景下，有两个问题：
1)、背景图常常是适应手机宽度缩放，而头像的尺寸又是固定宽高DP的，所以固定的蒙板图片是没法保证在不同机型上都和背景图案吻合的。
2)、在这种非纯色背景下，哪天想调整一下头像位置就得重新换图片蒙板，实在是太难维护了……
所以呢，既然头像图片肯定是方的，那就就让ImageView圆起来吧。
三、开始干活
基本思路是，自定义一个ImageView，通过重写onDraw方法画出一个圆形的图片来：
public class ImageViewPlus extends ImageView{
private Paint mPaintBitmap = new Paint(Paint.ANTI_ALIAS_FLAG);
private Bitmap mRawBitmap;
private BitmapShader mShader;
private Matrix mMatrix = new Matrix();
public ImageViewPlus(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
protected void onDraw(Canvas canvas) {
Bitmap rawBitmap = getBitmap(getDrawable());
if (rawBitmap != null){
int viewWidth = getWidth();
int viewHeight = getHeight();
int viewMinSize = Math.min(viewWidth, viewHeight);
float dstWidth = viewMinSize;
float dstHeight = viewMinSize;
if (mShader == null || !rawBitmap.equals(mRawBitmap)){
mRawBitmap = rawBitmap;
mShader = new BitmapShader(mRawBitmap, TileMode.CLAMP, TileMode.CLAMP);
}
if (mShader != null){
mMatrix.setScale(dstWidth / rawBitmap.getWidth(), dstHeight / rawBitmap.getHeight());
mShader.setLocalMatrix(mMatrix);
}
mPaintBitmap.setShader(mShader);
float radius = viewMinSize / 2.0f;
canvas.drawCircle(radius, radius, radius, mPaintBitmap);
} else {
super.onDraw(canvas);
}
}
private Bitmap getBitmap(Drawable drawable){
if (drawable instanceof BitmapDrawable){
return ((BitmapDrawable)drawable).getBitmap();
} else if (drawable instanceof ColorDrawable){
Rect rect = drawable.getBounds();
int width = rect.right - rect.left;
int height = rect.bottom - rect.top;
int color = ((ColorDrawable)drawable).getColor();
Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
canvas.drawARGB(Color.alpha(color), Color.red(color), Color.green(color), Color.blue(color));
return bitmap;
} else {
return null;
}
}
}
分析一下代码：
canvas.drawCircle 决定了画出来的形状是圆形，而圆形的内容则是通过 mPaintBitmap.setShader 搞定的。
其中，BitmapShader需要设置Bitmap填充ImageView的方式(CLAMP：拉伸边缘, MIRROR：镜像, REPEAT：整图重复)。
这里其实设成什么不重要，因为我们实际需要的是将Bitmap按比例缩放成跟ImageView一样大，而不是预置的三种效果。
所以，别忘了 mMatrix.setScale 和 mShader.setLocalMatrix 一起用，将图片缩放一下。
四、更多玩法 —— 支持边框
看下面的效果图，如果想给圆形的头像上加一个边框，该怎么搞呢？
public class ImageViewPlus extends ImageView{
private Paint mPaintBitmap = new Paint(Paint.ANTI_ALIAS_FLAG);
private Paint mPaintBorder = new Paint(Paint.ANTI_ALIAS_FLAG);
private Bitmap mRawBitmap;
private BitmapShader mShader;
private Matrix mMatrix = new Matrix();
private float mBorderWidth = dip2px(15);
private int mBorderColor = 0xFF0080FF;
public ImageViewPlus(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
protected void onDraw(Canvas canvas) {
Bitmap rawBitmap = getBitmap(getDrawable());
if (rawBitmap != null){
int viewWidth = getWidth();
int viewHeight = getHeight();
int viewMinSize = Math.min(viewWidth, viewHeight);
float dstWidth = viewMinSize;
float dstHeight = viewMinSize;
if (mShader == null || !rawBitmap.equals(mRawBitmap)){
mRawBitmap = rawBitmap;
mShader = new BitmapShader(mRawBitmap, TileMode.CLAMP, TileMode.CLAMP);
}
if (mShader != null){
mMatrix.setScale((dstWidth - mBorderWidth * 2) / rawBitmap.getWidth(), (dstHeight - mBorderWidth * 2) / rawBitmap.getHeight());
mShader.setLocalMatrix(mMatrix);
}
mPaintBitmap.setShader(mShader);
mPaintBorder.setStyle(Paint.Style.STROKE);
mPaintBorder.setStrokeWidth(mBorderWidth);
mPaintBorder.setColor(mBorderColor);
float radius = viewMinSize / 2.0f;
canvas.drawCircle(radius, radius, radius - mBorderWidth / 2.0f, mPaintBorder);
canvas.translate(mBorderWidth, mBorderWidth);
canvas.drawCircle(radius - mBorderWidth, radius - mBorderWidth, radius - mBorderWidth, mPaintBitmap);
} else {
super.onDraw(canvas);
}
}
private Bitmap getBitmap(Drawable drawable){
if (drawable instanceof BitmapDrawable){
return ((BitmapDrawable)drawable).getBitmap();
} else if (drawable instanceof ColorDrawable){
Rect rect = drawable.getBounds();
int width = rect.right - rect.left;
int height = rect.bottom - rect.top;
int color = ((ColorDrawable)drawable).getColor();
Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
canvas.drawARGB(Color.alpha(color), Color.red(color), Color.green(color), Color.blue(color));
return bitmap;
} else {
return null;
}
}
private int dip2px(int dipVal)
{
float scale = getResources().getDisplayMetrics().density;
return (int)(dipVal * scale + 0.5f);
}
}
看代码中，加边框实际上就是用实心纯色的 Paint 画了一个圆边，在此基础上画上原来的头像即可。
需要的注意的地方有三个：
1)、圆框的半径不是 radius ，而应该是 radius - mBorderWidth / 2.0f 。想象着拿着笔去画线，线其实是画在右图中白色圈的位置，只不过它很粗。
2)、在ImageView大小不变的基础上，头像的实际大小要比没有边框的时候小了，所以 mMatrix.setScale 的时候要把边框的宽度去掉。
3)、画头像Bitmap的时候不能直接 canvas.drawCircle(radius, radius, radius - mBorderWidth, mPaintBitmap) ，这样你会发现头像的右侧和下方边缘被拉伸了(右图)
为什么呢？因为 Paint 默认是以左上角为基准开始绘制的，此时头像的实际区域是右图中的红框，而超过红框的部分(圆形的右侧和下方)，自然被 TileMode.CLAMP效果沿边缘拉伸了。
所以，需要通过挪动坐标系的位置和调整圆心，才能把头像画在正确的区域(右图绿框)中。
五、更多玩法 —— 支持xml配置
既然有了边框，那如果想配置边框的宽度和颜色该如何是好呢？
基本上两个思路：
1)给ImageViewPlus加上set接口，设置完成之后通过 invalidate(); 重绘一下即可；
2)在xml里就支持配置一些自定义属性，这样用起来会方便很多。
这里重点说一下支持xml配置自定义属性。
自定义控件要支持xml配置自定义属性的话，首先需要在 \res\values 里去定义属性：
View attrs_imageviewplus.xml
然后在ImageViewPlus的构造函数中去读取这些自定义属性：
private static final int DEFAULT_BORDER_COLOR = Color.TRANSPARENT;
private static final int DEFAULT_BORDER_WIDTH = 0;
public ImageViewPlus(Context context, AttributeSet attrs) {
super(context, attrs);
//取xml文件中设定的参数
TypedArray ta = context.obtainStyledAttributes(attrs, R.styleable.ImageViewPlus);
mBorderColor = ta.getColor(R.styleable.ImageViewPlus_borderColor, DEFAULT_BORDER_COLOR);
mBorderWidth = ta.getDimensionPixelSize(R.styleable.ImageViewPlus_borderWidth, dip2px(DEFAULT_BORDER_WIDTH));
ta.recycle();
}
在xml布局中使用自定义属性：
xmlns:tools="http://schemas.android.com/tools"
xmlns:snser="http://schemas.android.com/apk/res/cc.snser.imageviewplus"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@drawable/wallpaper"
android:orientation="vertical"
tools:context="${relativePackage}.${activityClass}" >
android:id="@+id/imgplus"
android:layout_width="200dp"
android:layout_height="300dp"
android:layout_marginBottom="50dp"
android:layout_centerHorizontal="true"
android:layout_alignParentBottom="true"
android:src="@drawable/img_square"
snser:borderColor="#FF0080FF"
snser:borderWidth="15dp" />
六、更多玩法 —— 圆角ImageView
搞定了圆形ImageView以及对应的边框，那如何实现下面这种圆角的ImageView呢？
其实原理上一样，把 canvas.drawCircle 对应改成 canvas.drawRoundRect 就OK了，直接贴代码吧：
public class ImageViewPlus extends ImageView{
public static final int TYPE_NONE = 0;
public static final int TYPE_CIRCLE = 1;
public static final int TYPE_ROUNDED_RECT = 2;
private static final int DEFAULT_TYPE = TYPE_NONE;
private static final int DEFAULT_BORDER_COLOR = Color.TRANSPARENT;
private static final int DEFAULT_BORDER_WIDTH = 0;
private static final int DEFAULT_RECT_ROUND_RADIUS = 0;
private int mType;
private int mBorderColor;
private int mBorderWidth;
private int mRectRoundRadius;
private Paint mPaintBitmap = new Paint(Paint.ANTI_ALIAS_FLAG);
private Paint mPaintBorder = new Paint(Paint.ANTI_ALIAS_FLAG);
private RectF mRectBorder = new RectF();
private RectF mRectBitmap = new RectF();
private Bitmap mRawBitmap;
private BitmapShader mShader;
private Matrix mMatrix = new Matrix();
public ImageViewPlus(Context context, AttributeSet attrs) {
super(context, attrs);
//取xml文件中设定的参数
TypedArray ta = context.obtainStyledAttributes(attrs, R.styleable.ImageViewPlus);
mType = ta.getInt(R.styleable.ImageViewPlus_type, DEFAULT_TYPE);
mBorderColor = ta.getColor(R.styleable.ImageViewPlus_borderColor, DEFAULT_BORDER_COLOR);
mBorderWidth = ta.getDimensionPixelSize(R.styleable.ImageViewPlus_borderWidth, dip2px(DEFAULT_BORDER_WIDTH));
mRectRoundRadius = ta.getDimensionPixelSize(R.styleable.ImageViewPlus_rectRoundRadius, dip2px(DEFAULT_RECT_ROUND_RADIUS));
ta.recycle();
}
@Override
protected void onDraw(Canvas canvas) {
Bitmap rawBitmap = getBitmap(getDrawable());
if (rawBitmap != null && mType != TYPE_NONE){
int viewWidth = getWidth();
int viewHeight = getHeight();
int viewMinSize = Math.min(viewWidth, viewHeight);
float dstWidth = mType == TYPE_CIRCLE ? viewMinSize : viewWidth;
float dstHeight = mType == TYPE_CIRCLE ? viewMinSize : viewHeight;
float halfBorderWidth = mBorderWidth / 2.0f;
float doubleBorderWidth = mBorderWidth * 2;
if (mShader == null || !rawBitmap.equals(mRawBitmap)){
mRawBitmap = rawBitmap;
mShader = new BitmapShader(mRawBitmap, TileMode.CLAMP, TileMode.CLAMP);
}
if (mShader != null){
mMatrix.setScale((dstWidth - doubleBorderWidth) / rawBitmap.getWidth(), (dstHeight - doubleBorderWidth) / rawBitmap.getHeight());
mShader.setLocalMatrix(mMatrix);
}
mPaintBitmap.setShader(mShader);
mPaintBorder.setStyle(Paint.Style.STROKE);
mPaintBorder.setStrokeWidth(mBorderWidth);
mPaintBorder.setColor(mBorderWidth > 0 ? mBorderColor : Color.TRANSPARENT);
if (mType == TYPE_CIRCLE){
float radius = viewMinSize / 2.0f;
canvas.drawCircle(radius, radius, radius - halfBorderWidth, mPaintBorder);
canvas.translate(mBorderWidth, mBorderWidth);
canvas.drawCircle(radius - mBorderWidth, radius - mBorderWidth, radius - mBorderWidth, mPaintBitmap);
} else if (mType == TYPE_ROUNDED_RECT){
mRectBorder.set(halfBorderWidth, halfBorderWidth, dstWidth - halfBorderWidth, dstHeight - halfBorderWidth);
mRectBitmap.set(0.0f, 0.0f, dstWidth - doubleBorderWidth, dstHeight - doubleBorderWidth);
float borderRadius = mRectRoundRadius - halfBorderWidth > 0.0f ? mRectRoundRadius - halfBorderWidth : 0.0f;
float bitmapRadius = mRectRoundRadius - mBorderWidth > 0.0f ? mRectRoundRadius - mBorderWidth : 0.0f;
canvas.drawRoundRect(mRectBorder, borderRadius, borderRadius, mPaintBorder);
canvas.translate(mBorderWidth, mBorderWidth);
canvas.drawRoundRect(mRectBitmap, bitmapRadius, bitmapRadius, mPaintBitmap);
}
} else {
super.onDraw(canvas);
}
}
private int dip2px(int dipVal)
{
float scale = getResources().getDisplayMetrics().density;
return (int)(dipVal * scale + 0.5f);
}
private Bitmap getBitmap(Drawable drawable){
if (drawable instanceof BitmapDrawable){
return ((BitmapDrawable)drawable).getBitmap();
} else if (drawable instanceof ColorDrawable){
Rect rect = drawable.getBounds();
int width = rect.right - rect.left;
int height = rect.bottom - rect.top;
int color = ((ColorDrawable)drawable).getColor();
Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
canvas.drawARGB(Color.alpha(color), Color.red(color), Color.green(color), Color.blue(color));
return bitmap;
} else {
return null;
}
}
}
View ImageViewPlus.java
xmlns:tools="http://schemas.android.com/tools"
xmlns:snser="http://schemas.android.com/apk/res/cc.snser.imageviewplus"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@drawable/wallpaper"
android:orientation="vertical"
tools:context="${relativePackage}.${activityClass}" >
android:id="@+id/imgplus"
android:layout_width="200dp"
android:layout_height="300dp"
android:layout_marginBottom="50dp"
android:layout_centerHorizontal="true"
android:layout_alignParentBottom="true"
android:src="@drawable/img_rectangle"
snser:type="rounded_rect"
snser:borderColor="#FF0080FF"
snser:borderWidth="10dp"
snser:rectRoundRadius="30dp" />
View layout
View attrs_imageviewplus.xml
以上就是本文的全部内容，希望对大家学习Android软件编程有所帮助。