自定义控件学习第二课

自定义控件学习第二课
这节课效果如下：

第一步还是先写属性文件

<?xml version="1.0" encoding="utf-8"?><resources>    <attr name="titleText" format="string"/>    <attr name="titleTextSize" format="dimension"/>    <attr name="titleTextColor" format="color"/>    <attr name="image" format="reference"/>    <attr name="imageScaleType">        <enum name="fillXY" value="0"/>        <enum name="center" value="1"/>    </attr>    <declare-styleable name="CustomImageView">        <attr name="titleText"/>        <attr name="titleTextSize"/>        <attr name="titleTextColor"/>        <attr name="image"/>        <attr name="imageScaleType"/>    </declare-styleable></resources>

第二步实现类：

public class CustomImageView extends View {    private String mTitleText;    private int mTitleTextSize;    private int mTitleTextColor;    private Bitmap mImage;    private int mImageScaleType;    private Paint mPaint;    private Rect mBound;    private Rect rect;// 可绘制的范围    private int mWidth;    private int mHeight;    public CustomImageView(Context context) {        this(context, null);        // TODO Auto-generated constructor stub    }    public CustomImageView(Context context, AttributeSet attrs) {        this(context, attrs, 0);        // TODO Auto-generated constructor stub    }    public CustomImageView(Context context, AttributeSet attrs, int defStyle) {        super(context, attrs, defStyle);        // TODO Auto-generated constructor stub        TypedArray a = context.getTheme().obtainStyledAttributes(attrs,                R.styleable.CustomImageView, defStyle, 0);        int n = a.getIndexCount();        for (int i = 0; i < n; i++) {            int attr = a.getIndex(i);            switch (attr) {            case R.styleable.CustomImageView_titleText:                mTitleText = a.getString(attr);                break;            case R.styleable.CustomImageView_titleTextSize:                mTitleTextSize = a.getDimensionPixelSize(attr, (int) TypedValue                        .applyDimension(TypedValue.COMPLEX_UNIT_SP, 16,                                getResources().getDisplayMetrics()));                break;            case R.styleable.CustomImageView_titleTextColor:                mTitleTextColor = a.getColor(attr, Color.BLACK);                break;            case R.styleable.CustomImageView_image:                mImage = BitmapFactory.decodeResource(getResources(),                        a.getResourceId(attr, 0));                break;            case R.styleable.CustomImageView_imageScaleType:                mImageScaleType = a.getInt(attr, 0);                break;            }        }        a.recycle();        mPaint = new Paint();        mBound = new Rect();        rect = new Rect();        mPaint.setTextSize(mTitleTextSize);        mPaint.getTextBounds(mTitleText, 0, mTitleText.length(), mBound);    }    @Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {        // TODO Auto-generated method stub        /*         * 处理宽度         */        int widthMode = MeasureSpec.getMode(widthMeasureSpec);        int widthSize = MeasureSpec.getSize(widthMeasureSpec);        if (widthMode == MeasureSpec.EXACTLY) {            mWidth = widthSize;        } else {            int widthByImg = mImage.getWidth() + getPaddingLeft()                    + getPaddingRight();            int widthByText = mBound.width() + getPaddingLeft()                    + getPaddingRight();            if (widthMode == MeasureSpec.AT_MOST) {                mWidth = Math.min(widthSize, Math.max(widthByImg, widthByText));            }        }        /*         * 处理高度         */        int heightMode = MeasureSpec.getMode(heightMeasureSpec);        int heightSize = MeasureSpec.getSize(heightMeasureSpec);        if (heightMode == MeasureSpec.EXACTLY) {            mHeight = heightSize;        } else {            int heightImgAddText = getPaddingTop() + getPaddingBottom()                    + mImage.getHeight() + mBound.width();            if (heightMode == MeasureSpec.AT_MOST) {                mHeight = Math.min(heightSize, heightImgAddText);            }        }        setMeasuredDimension(mWidth, mHeight);    }    @Override    protected void onDraw(Canvas canvas) {        // TODO Auto-generated method stub        // 边框        mPaint.setStrokeWidth(4);        mPaint.setStyle(Paint.Style.STROKE);        mPaint.setColor(Color.CYAN);        canvas.drawRect(0, 0, getMeasuredWidth(), getMeasuredHeight(), mPaint);        // 画字        mPaint.setColor(mTitleTextColor);        mPaint.setStyle(Paint.Style.FILL);        if (mBound.width() > mWidth) {// 字的范围超出当前设置范围了            TextPaint p = new TextPaint(mPaint);            String msg = TextUtils.ellipsize(mTitleText, p,                    (float) mWidth - getPaddingLeft() - getPaddingRight(),                    TextUtils.TruncateAt.END).toString();            canvas.drawText(msg, getPaddingLeft(), mHeight                    - getPaddingBottom(), mPaint);        } else {// 正常，则居中显示            canvas.drawText(mTitleText, mWidth / 2 - mBound.width() / 2,                    mHeight - getPaddingBottom(), mPaint);        }        // 只考虑字的宽度，保证字的高度，确保显示        rect.left = getPaddingLeft();        rect.right = mWidth - getPaddingRight();        rect.top = getPaddingTop();        rect.bottom = mHeight - getPaddingBottom() - mBound.height();        // 现在rect就是图片可显示的大小了        if (mImageScaleType == 0) {            canvas.drawBitmap(mImage, null, rect, mPaint);        } else {            rect.left = mWidth / 2 - mImage.getWidth() / 2;            rect.right = mWidth / 2 + mImage.getWidth() / 2;            rect.top = (mHeight - mBound.height()) / 2 - mImage.getHeight() / 2;            rect.bottom = (mHeight - mBound.height()) / 2 + mImage.getHeight()                    / 2;            canvas.drawBitmap(mImage, null, rect, mPaint);        }    }}

其中有些知识点讲下：
TextUtils类介绍
对于字符串处理Android为我们提供了一个简单实用的TextUtils类，如果处理比较简单的内容不用去思考正则表达式不妨试试这个在android.text.TextUtils的类，主要的功能如下:
是否为空字符 boolean android.text.TextUtils.isEmpty(CharSequence str)
拼接字符串 String android.text.TextUtils.join(CharSequence delimiter, Object[] tokens)
拆分字符串 String[] android.text.TextUtils.split(String text, String expression)
拆分字符串使用正则 String[] android.text.TextUtils.split(String text, Pattern pattern)
确定大小写是否有效在当前位置的文本 int android.text.TextUtils.getCapsMode(CharSequence cs, int off, int reqModes)
使用HTML编码这个字符串 String android.text.TextUtils.htmlEncode(String s)
另外，String[] android.text.TextUtils.split(String text, String expression)中的expression较特殊，如果采用
TextUtils.split(someString, “-“);
来分割someString的话返回的将是错误结果，正确的用法应该是
TextUtils.split(line, “,|\-“);

对图片剪接和限定显示区域

drawBitmap(Bitmap bitmap, Rect src, RectF dst, Paint paint)；
Rect src: 是对图片进行裁截，若是空null则显示整个图片
RectF dst：是图片在Canvas画布中显示的区域，
大于src则把src的裁截区放大，
小于src则把src的裁截区缩小。