第一步 自定義控件屬性

首先在res/values/attrs

<declare-styleable name="GradientTextView">
        <attr name="text_size" format="dimension"/>
        <attr name="text_style" format="reference|integer"/>
        <attr name="is_can_grandient" format="boolean"/>
        <attr name="text_color" format="color|reference"/>
        <attr name="gravity" format="integer"/>
        <attr name="max_width" format="dimension"/>
        <attr name="start_color" format="color|reference"/>
        <attr name="end_color" format="color|reference"/>
        <attr name="angle" format="integer"/>
        <attr name="text" format="string"/>
    </declare-styleable>

第二步 從構(gòu)造方法里面去獲取自定義的屬性值

public GradientTextView(Context context) {
        super(context);
        init(context, null);
    }

    public GradientTextView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init(context, attrs);
    }

    public GradientTextView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context, attrs);
    }

    private void init(Context context, @Nullable AttributeSet attrs) {
        if(attrs == null) {
            return;
        }
        TypedArray typedArray = context.obtainStyledAttributes(attrs,R.styleable.GradientTextView);
        mIsCanGrandient = typedArray.getBoolean(R.styleable.GradientTextView_is_can_grandient,false);
        mText = typedArray.getString(R.styleable.GradientTextView_text);
        mTextSize = typedArray.getDimensionPixelSize(R.styleable.GradientTextView_text_size, mTextSize);
        mAngle = typedArray.getInt(R.styleable.SGradientTextView_angle, -1);
        mTextColor = typedArray.getColor(R.styleable.GradientTextView_text_color,Color.BLACK);
        color[0] = typedArray.getColor(R.styleable.GradientTextView_start_color,Color.BLACK);
        color[1] = typedArray.getColor(R.styleable.GradientTextView_end_color,Color.BLACK);
        mGravity = typedArray.getInt(R.styleable.GradientTextView_gravity, Gravity.LEFT);
        mMaxWidth = typedArray.getDimensionPixelSize(R.styleable.GradientTextView_max_width, Integer.MAX_VALUE);
        textStyle = typedArray.getInt(R.styleable.GradientTextView_text_style, Typeface.NORMAL);
        setPaintAttrs();
        typedArray.recycle();
    }

第三步 重寫方法

@Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int measureWidth = measureWidth(widthMeasureSpec);
        int measureHeight = measureHeight(heightMeasureSpec);
        setMeasuredDimension(measureWidth, measureHeight);
        mMeasuredWidth = getMeasuredWidth();
        mMeasuredHeight = getMeasuredHeight();
    }

@Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        final float desiredTextWidth = mPaint.measureText(mText);
        final float maxTextWidth = mMeasuredWidth - getPaddingLeft() - getPaddingRight();
        if (mIsCanGrandient) {
            if (mAngle >= 0) {
                Rect rect = new Rect();
                mPaint.getTextBounds(mText,0,mText.length(), rect);
                changeGradientColor(mAngle, rect.width(), rect.height());
                LinearGradient gradient = new LinearGradient(startX, startY, endX, endY, color[0], color[1], Shader.TileMode.CLAMP);
                mPaint.setShader(gradient);
            }else {
                setPaintAttrs();
            }
        }
        if (desiredTextWidth > maxTextWidth) {
            float scaleX = maxTextWidth / desiredTextWidth;
            if (scaleX > RATIO_THRESHOLD) {
                scaleX *= 0.98f;
                mPaint.setTextScaleX(scaleX);
            } else {
                mPaint.setTextScaleX(scaleX);
                float ellipsisLength = mPaint.measureText("...");
                int drawCharsCount = mPaint.breakText(mText, true, maxTextWidth - ellipsisLength, new float[0]);
                mText = mText.substring(0, drawCharsCount) + "...";
            }
        }
        Paint.FontMetrics fontMetrics = mPaint.getFontMetrics();
        final float fontBaseLine = (getPaddingTop() + mMeasuredHeight - getPaddingBottom()) / 2 + (fontMetrics.bottom - fontMetrics.top) / 2 - fontMetrics.bottom;
        if (mGravity == Gravity.RIGHT) {
            final float targetTextWidth = mPaint.measureText(mText);
            canvas.drawText(mText, mMeasuredWidth - getPaddingRight() - targetTextWidth, fontBaseLine, mPaint);
        } else if (mGravity == Gravity.CENTER) {
            final float targetTextWidth = mPaint.measureText(mText);
            canvas.drawText(mText, (getPaddingLeft() + mMeasuredWidth - getPaddingRight()) / 2 - targetTextWidth / 2, fontBaseLine, mPaint);
        } else {
            canvas.drawText(mText, getPaddingLeft(), fontBaseLine, mPaint);
        }


    }

以下是全部的代碼

class GradientTextView extends View {
    private static final float RATIO_THRESHOLD = 1.0f / 2;
    private int mTextSize = dpToPx(12);
    private int mTextColor;
    private int mMeasuredWidth, mMeasuredHeight, mMaxWidth = Integer.MAX_VALUE;
    private TextPaint mPaint = new TextPaint();
    private String mText = "";
    private int mGravity;
    private int[] color = new int[]{Color.BLACK,Color.BLACK};
    private float startX,startY,endX,endY;
    //漸變色的角度值
    private int mAngle;
    //是否開啟漸變效果
    private boolean mIsCanGrandient;
    private int textStyle;

    public GradientTextView(Context context) {
        super(context);
        init(context, null);
    }

    public GradientTextView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init(context, attrs);
    }

    public GradientTextView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context, attrs);
    }

    private void init(Context context, @Nullable AttributeSet attrs) {
        if(attrs == null) {
            return;
        }
        TypedArray typedArray = context.obtainStyledAttributes(attrs,R.styleable.GradientTextView);
        mIsCanGrandient = typedArray.getBoolean(R.styleable.GradientTextView_is_can_grandient,false);
        mText = typedArray.getString(R.styleable.GradientTextView_text);
        mTextSize = typedArray.getDimensionPixelSize(R.styleable.GradientTextView_text_size, mTextSize);
        mAngle = typedArray.getInt(R.styleable.SGradientTextView_angle, -1);
        mTextColor = typedArray.getColor(R.styleable.GradientTextView_text_color,Color.BLACK);
        color[0] = typedArray.getColor(R.styleable.GradientTextView_start_color,Color.BLACK);
        color[1] = typedArray.getColor(R.styleable.GradientTextView_end_color,Color.BLACK);
        mGravity = typedArray.getInt(R.styleable.GradientTextView_gravity, Gravity.LEFT);
        mMaxWidth = typedArray.getDimensionPixelSize(R.styleable.GradientTextView_max_width, Integer.MAX_VALUE);
        textStyle = typedArray.getInt(R.styleable.GradientTextView_text_style, Typeface.NORMAL);
        setPaintAttrs();
        typedArray.recycle();
    }

    /**
     * 設(shè)置paint的屬性樣式
     */
    private void setPaintAttrs(){
        mPaint.reset();
        mPaint.setColor(mTextColor);
        mPaint.setTextSize(mTextSize);
        mPaint.setAntiAlias(true);
        mPaint.setTypeface(getTypeface(textStyle));
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int measureWidth = measureWidth(widthMeasureSpec);
        int measureHeight = measureHeight(heightMeasureSpec);
        setMeasuredDimension(measureWidth, measureHeight);
        mMeasuredWidth = getMeasuredWidth();
        mMeasuredHeight = getMeasuredHeight();
    }

    private int measureHeight(int heightMeasureSpec) {
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        int heightSize = MeasureSpec.getSize(heightMeasureSpec);
        int result = heightSize;
        switch (heightMode) {
            case MeasureSpec.UNSPECIFIED:
            case MeasureSpec.AT_MOST:
                Paint.FontMetricsInt fontMetricsInt = mPaint.getFontMetricsInt();
                result = fontMetricsInt.bottom - fontMetricsInt.top + getPaddingTop() + getPaddingBottom();
                break;
            case MeasureSpec.EXACTLY:
                result = heightSize;
                break;
        }
        return result;
    }

    private int measureWidth(int widthMeasureSpec) {
        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        int widthSize = MeasureSpec.getSize(widthMeasureSpec);
        int result = widthSize;
        switch (widthMode) {
            case MeasureSpec.UNSPECIFIED:
            case MeasureSpec.AT_MOST:
                result = (int) (mPaint.measureText(mText) + getPaddingLeft() + getPaddingRight());
                if (result > mMaxWidth) {
                    result = mMaxWidth;
                }
                break;
            case MeasureSpec.EXACTLY:
                result = widthSize;
                break;
        }
        return result;
    }

    public void setText(String text) {
        if (text == null) {
            text = "";
        }
        if (text.equals(mText)) {
            return;
        }
        mText = text;
        mPaint.setTextScaleX(1.0f);
        requestLayout();
        invalidate();
    }

    public void setTextColor(int color) {
        mTextColor = color;
        mPaint.setColor(mTextColor);
        invalidate();
    }

    /**
     * 是否開啟漸變效果
     * @param isCanGradient
     */
    public void setIsCanGradient(boolean isCanGradient){
        mIsCanGrandient = isCanGradient;
        invalidate();
    }

    /**
     * 漸變色值
     * @param startColor
     * @param endColor
     */
    public void setGradientColor(int startColor,int endColor){
        color[0] = startColor;
        color[1] = endColor;
        invalidate();
    }
    /**
     * 顏色漸變
     * @param angle
     * 0從左到右
     * 90 從下到上
     * 180 從右到左
     * 270 從上到下
     */
    public void setGradient(int angle){
        mAngle = angle;
        invalidate();
    }

    /**
     * 通過不同的角度改變漸變色的起始方向
     * @param angle
     * @param width
     * @param height
     */
    private void changeGradientColor(int angle,float width,float height){
        if ((angle % 90) != 0){
            throw new IllegalArgumentException("The parameter must be a multiple of 90");
        }
        switch (angle % 360){
            case 0:
                startX = 0;
                startY = (float) (height *0.5);
                endX = width;
                endY = (float) (height *0.5);
                break;
            case 90:
                startX = (float) (width *0.5);
                startY = height;
                endX = (float) (width *0.5);
                endY = 0;

                break;
            case 180:
                startX = width;
                startY = (float) (height *0.5);
                endX = 0;
                endY = (float) (height *0.5);
                break;
            case 270:
                startX = (float) (width *0.5);
                startY = 0;
                endX = (float) (width *0.5);
                endY = height;
                break;
        }
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        final float desiredTextWidth = mPaint.measureText(mText);
        final float maxTextWidth = mMeasuredWidth - getPaddingLeft() - getPaddingRight();
        if (mIsCanGrandient) {
            if (mAngle >= 0) {
                Rect rect = new Rect();
                mPaint.getTextBounds(mText,0,mText.length(), rect);
                changeGradientColor(mAngle, rect.width(), rect.height());
                LinearGradient gradient = new LinearGradient(startX, startY, endX, endY, color[0], color[1], Shader.TileMode.CLAMP);
                mPaint.setShader(gradient);
            }else {
                setPaintAttrs();
            }
        }
        if (desiredTextWidth > maxTextWidth) {
            float scaleX = maxTextWidth / desiredTextWidth;
            if (scaleX > RATIO_THRESHOLD) {
                scaleX *= 0.98f;
                mPaint.setTextScaleX(scaleX);
            } else {
                mPaint.setTextScaleX(scaleX);
                float ellipsisLength = mPaint.measureText("...");
                int drawCharsCount = mPaint.breakText(mText, true, maxTextWidth - ellipsisLength, new float[0]);
                mText = mText.substring(0, drawCharsCount) + "...";
            }
        }
        Paint.FontMetrics fontMetrics = mPaint.getFontMetrics();
        final float fontBaseLine = (getPaddingTop() + mMeasuredHeight - getPaddingBottom()) / 2 + (fontMetrics.bottom - fontMetrics.top) / 2 - fontMetrics.bottom;
        if (mGravity == Gravity.RIGHT) {
            final float targetTextWidth = mPaint.measureText(mText);
            canvas.drawText(mText, mMeasuredWidth - getPaddingRight() - targetTextWidth, fontBaseLine, mPaint);
        } else if (mGravity == Gravity.CENTER) {
            final float targetTextWidth = mPaint.measureText(mText);
            canvas.drawText(mText, (getPaddingLeft() + mMeasuredWidth - getPaddingRight()) / 2 - targetTextWidth / 2, fontBaseLine, mPaint);
        } else {
            canvas.drawText(mText, getPaddingLeft(), fontBaseLine, mPaint);
        }


    }

    private static Typeface getTypeface(int textStyle) {
        Typeface typeface;
        switch (textStyle) {
            case Typeface.NORMAL:// 正常字體.
            default:
                typeface = Typeface.DEFAULT;
                break;
            case Typeface.BOLD:// 加粗字體.
                typeface = Typeface.DEFAULT_BOLD;
                break;
            case Typeface.ITALIC:// 傾斜字體.
                typeface = Typeface.create(Typeface.DEFAULT, Typeface.ITALIC);
                break;
            case Typeface.BOLD_ITALIC:// 加粗傾斜字體.
                typeface = Typeface.create(Typeface.DEFAULT, Typeface.BOLD_ITALIC);
        }
        return typeface;
    }

    private int dpToPx(int dps) {
        return Math.round(getResources().getDisplayMetrics().density * dps);
    }
}

支持屬性設(shè)置，方法更改相應(yīng)的要求，里面只要是用到了LinearGradient 這個方法來設(shè)置，只支持90的倍數(shù)，具體的角度更改設(shè)值在setGradient()方法里面有解釋