Android实战简易教程-第六十一枪（圆形显示的ImageView）

ImageView在我们的项目中经常使用，一般ImageView是正方形的，要使用圆形的ImageView可以通过自定义View来实现，下面我们介绍一下如何实现。

1.CircularImageView.java 继承自ImageView:

package com.yayun.circularimageview;

import com.mikhaellopez.circularimageview.R;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Bitmap;
import android.graphics.BitmapShader;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Shader;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.widget.ImageView;

public class CircularImageView extends ImageView {
	private int borderWidth;
	private int canvasSize;
	private Bitmap image;
	private Paint paint;
	private Paint paintBorder;

	public CircularImageView(final Context context) {
		this(context, null);
	}

	public CircularImageView(Context context, AttributeSet attrs) {
		this(context, attrs, R.attr.circularImageViewStyle);
	}

	public CircularImageView(Context context, AttributeSet attrs, int defStyle) {
		super(context, attrs, defStyle);

		// init paint
		paint = new Paint();
		paint.setAntiAlias(true);

		paintBorder = new Paint();
		paintBorder.setAntiAlias(true);// 抗锯齿

		TypedArray attributes = context.obtainStyledAttributes(attrs,
				R.styleable.CircularImageView, defStyle, 0);

		/**
		 * 有边框
		 */
		if (attributes.getBoolean(R.styleable.CircularImageView_border, true)) {
			int defaultBorderSize = (int) (4 * getContext().getResources()
					.getDisplayMetrics().density + 0.5f);// 默认宽度
			setBorderWidth(attributes.getDimensionPixelOffset(
					R.styleable.CircularImageView_border_width,
					defaultBorderSize));// 边框大小
			setBorderColor(attributes.getColor(
					R.styleable.CircularImageView_border_color, Color.WHITE));// 边框颜色
		}

		/**
		 * 无边框
		 */
		if (attributes.getBoolean(R.styleable.CircularImageView_shadow, false))
			addShadow();
	}

	/**
	 * 设置边框宽度
	 * 
	 * @param borderWidth
	 */
	public void setBorderWidth(int borderWidth) {
		this.borderWidth = borderWidth;
		this.requestLayout();
		this.invalidate();
	}

	/**
	 * 设置边框颜色
	 * 
	 * @param borderColor
	 */
	public void setBorderColor(int borderColor) {
		if (paintBorder != null)
			paintBorder.setColor(borderColor);
		this.invalidate();
	}

	public void addShadow() {
		setLayerType(LAYER_TYPE_SOFTWARE, paintBorder);
		paintBorder.setShadowLayer(4.0f, 0.0f, 2.0f, Color.BLACK);
	}

	@Override
	public void onDraw(Canvas canvas) {
		// load the bitmap
		image = drawableToBitmap(getDrawable());

	
		if (image != null) {

			canvasSize = canvas.getWidth();
			if (canvas.getHeight() < canvasSize)// 取小值
				canvasSize = canvas.getHeight();

			BitmapShader shader = new BitmapShader(Bitmap.createScaledBitmap(
					image, canvasSize, canvasSize, false),
					Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);
			paint.setShader(shader);

	
			/**
			 * 圆心
			 */
			int circleCenter = (canvasSize - (borderWidth * 2)) / 2;
			// void android.graphics.Canvas.drawCircle(float cx, float cy, float radius, Paint paint)
			canvas.drawCircle(circleCenter + borderWidth, circleCenter
					+ borderWidth, ((canvasSize - (borderWidth * 2)) / 2)
					+ borderWidth - 4.0f, paintBorder);
			canvas.drawCircle(circleCenter + borderWidth, circleCenter
					+ borderWidth,
					((canvasSize - (borderWidth * 2)) / 2) - 4.0f, paint);
		}
	}

	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
		int width = measureWidth(widthMeasureSpec);
		int height = measureHeight(heightMeasureSpec);
		setMeasuredDimension(width, height);
	}

	private int measureWidth(int measureSpec) {
		int result = 0;
		int specMode = MeasureSpec.getMode(measureSpec);
		int specSize = MeasureSpec.getSize(measureSpec);

		if (specMode == MeasureSpec.EXACTLY) {
			// The parent has determined an exact size for the child.
			result = specSize;
		} else if (specMode == MeasureSpec.AT_MOST) {
			// The child can be as large as it wants up to the specified size.
			result = specSize;
		} else {
			// The parent has not imposed any constraint on the child.
			result = canvasSize;
		}

		return result;
	}

	private int measureHeight(int measureSpecHeight) {
		int result = 0;
		int specMode = MeasureSpec.getMode(measureSpecHeight);
		int specSize = MeasureSpec.getSize(measureSpecHeight);

		if (specMode == MeasureSpec.EXACTLY) {
			// We were told how big to be
			result = specSize;
		} else if (specMode == MeasureSpec.AT_MOST) {
			// The child can be as large as it wants up to the specified size.
			result = specSize;
		} else {
			// Measure the text (beware: ascent is a negative number)
			result = canvasSize;
		}

		return (result + 2);
	}

	/**
	 * 获取bitmap
	 * 
	 * @param drawable
	 * @return
	 */
	public Bitmap drawableToBitmap(Drawable drawable) {
		if (drawable == null) {
			return null;
		} else if (drawable instanceof BitmapDrawable) {
			return ((BitmapDrawable) drawable).getBitmap();
		}

		Bitmap bitmap = Bitmap.createBitmap(drawable.getIntrinsicWidth(),
				drawable.getIntrinsicHeight(), Bitmap.Config.ARGB_8888);
		Canvas canvas = new Canvas(bitmap);
		drawable.setBounds(0, 0, canvas.getWidth(), canvas.getHeight());
		drawable.draw(canvas);

		return bitmap;
	}
}

知识：一般来说，自定义控件都会去重写View的onMeasure方法，因为该方法指定该控件在屏幕上的大小。

protected void?onMeasure?(int widthMeasureSpec, int heightMeasureSpec)

onMeasure传入的两个参数是由上一层控件传入的大小，有多种情况，重写该方法时需要对计算控件的实际大小，然后调用setMeasuredDimension(int, int)设置实际大小。

onMeasure传入的widthMeasureSpec和heightMeasureSpec不是一般的尺寸数值，而是将模式和尺寸组合在一起的数值。我们需要通过int mode = MeasureSpec.getMode(widthMeasureSpec)得到模式，用int size =?MeasureSpec.getSize(widthMeasureSpec)得到尺寸。

mode共有三种情况，取值分别为

MeasureSpec.UNSPECIFIED, MeasureSpec.EXACTLY, MeasureSpec.AT_MOST。

MeasureSpec.EXACTLY是精确尺寸，当我们将控件的layout_width或layout_height指定为具体数值时如andorid:layout_width="50dip"，或者为FILL_PARENT是，都是控件大小已经确定的情况，都是精确尺寸。

MeasureSpec.AT_MOST是最大尺寸，当控件的layout_width或layout_height指定为WRAP_CONTENT时，控件大小一般随着控件的子空间或内容进行变化，此时控件尺寸只要不超过父控件允许的最大尺寸即可。因此，此时的mode是AT_MOST，size给出了父控件允许的最大尺寸。

MeasureSpec.UNSPECIFIED是未指定尺寸，这种情况不多，一般都是父控件是AdapterView，通过measure方法传入的模式。

2.属性文件：

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <declare-styleable name="CircularImageView">
        <attr name="border" format="boolean"></attr>
        <attr name="border_width" format="dimension"></attr>
        <attr name="border_color" format="color"></attr>
        <attr name="shadow" format="boolean"></attr>
    </declare-styleable>
    
    <declare-styleable name="Theme">
        <attr name="circularImageViewStyle" format="reference"></attr>
    </declare-styleable>

</resources>

3.我们在布局文件中引用：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res/com.mikhaellopez.circularimageviewsample"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:gravity="center"
    android:orientation="vertical" >

    <com.yayun.circularimageview.CircularImageView
        android:layout_width="250dp"
        android:layout_height="250dp"
        android:src="@drawable/image"
        app:border="true"
        app:border_color="@color/Blue"
        app:border_width="14dp"
        app:shadow="true" />
    
    <com.yayun.circularimageview.CircularImageView
        android:layout_width="200dp"
        android:layout_height="200dp"
        android:src="@drawable/image"
         />

</LinearLayout>

运行实例效果如下：

第一个图片有边框的效果，可以自行设置。

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