android实现文字渐变效果和歌词进度的效果

android实现文字渐变效果和歌词进度的效果

要用TextView使用渐变色，那我们就必须要了解LinearGradient（线性渐变）的用法。

LinearGradient的参数解释

LinearGradient也称作线性渲染，LinearGradient的作用是实现某一区域内颜色的线性渐变效果，看源码你就知道他是shader的子类。

它有两个构造函数

public LinearGradient(float x0, float y0, float x1, float y1, int color0, int color1, Shader.TileMode tile)


public LinearGradient (float x0, float y0, float x1, float y1, int[] colors, float[] positions, Shader.TileMode tile);

其中，参数x0表示渐变的起始点x坐标；参数y0表示渐变的起始点y坐标；参数x1表示渐变的终点x坐标；参数y1表示渐变的终点y坐标　；color0表示渐变开始颜色；color1表示渐变结束颜色；参数tile表示平铺方式。

Shader.TileMode有3种参数可供选择，分别为CLAMP、REPEAT和MIRROR：

CLAMP的作用是如果渲染器超出原始边界范围，则会复制边缘颜色对超出范围的区域进行着色

REPEAT的作用是在横向和纵向上以平铺的形式重复渲染位图

MIRROR的作用是在横向和纵向上以镜像的方式重复渲染位图

LinearGradient的简单使用

先实现文字效果的水平渐变：

Shader shader_horizontal= new LinearGradient(btWidth/4, 0, btWidth, 0, Color.RED, Color.GREEN, Shader.TileMode.CLAMP);
                tv_text_horizontal.getPaint().setShader(shader_horizontal);

再实现文字的垂直渐变效果：

Shader shader_vertical=new LinearGradient(0, btHeight/4, 0, btHeight, Color.RED, Color.GREEN, Shader.TileMode.CLAMP);
                tv_text_vertical.getPaint().setShader(shader_vertical);

接下来来实现文字的颜色动态渐变效果：<喎?http://www.Bkjia.com/kf/ware/vc/" target="_blank" class="keylink">vcD4NCjxwcmUgY2xhc3M9"brush:java;"> import android.content.Context; import android.graphics.Canvas; import android.graphics.LinearGradient; import android.graphics.Matrix; import android.graphics.Paint; import android.graphics.Shader; import android.util.AttributeSet; import android.widget.TextView; /** * Created on 2016/3/13. */ public class GradientHorizontalTextView extends TextView { private LinearGradient mLinearGradient; private Matrix mGradientMatrix;//渐变矩阵 private Paint mPaint;//画笔 private int mViewWidth = 0;//textView的宽 private int mTranslate = 0;//平移量 private boolean mAnimating = true;//是否动画 private int delta = 15;//移动增量 public GradientHorizontalTextView(Context ctx) { this(ctx,null); } public GradientHorizontalTextView(Context context, AttributeSet attrs) { super(context, attrs); } @Override protected void onSizeChanged(int w, int h, int oldw, int oldh) { super.onSizeChanged(w, h, oldw, oldh); if (mViewWidth == 0) { mViewWidth = getMeasuredWidth(); if (mViewWidth > 0) { mPaint = getPaint(); String text = getText().toString(); int size; if(text.length()>0) { size = mViewWidth*2/text.length(); }else{ size = mViewWidth; } mLinearGradient = new LinearGradient(-size, 0, 0, 0, new int[] { 0x33ffffff, 0xffffffff, 0x33ffffff }, new float[] { 0, 0.5f, 1 }, Shader.TileMode.CLAMP); //边缘融合 mPaint.setShader(mLinearGradient);//设置渐变 mGradientMatrix = new Matrix(); } } } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); if (mAnimating && mGradientMatrix != null) { float mTextWidth = getPaint().measureText(getText().toString());//获得文字宽 mTranslate += delta;//默认向右移动 if (mTranslate > mTextWidth+1 || mTranslate<1) { delta = -delta;//向左移动 } mGradientMatrix.setTranslate(mTranslate, 0); mLinearGradient.setLocalMatrix(mGradientMatrix); postInvalidateDelayed(30);//刷新 } } }

实现歌词进度效果

Canvas 作为绘制文本时，使用FontMetrics对象，计算位置的坐标。它的思路和java.awt.FontMetrics的基本相同。
FontMetrics对象它以四个基本坐标为基准，分别为：

FontMetrics.top
FontMetrics.ascent
FontMetrics.descent
FontMetrics.bottom

// FontMetrics对象
  FontMetrics fontMetrics = textPaint.getFontMetrics();  
  String text = "abcdefghijklmnopqrstu";  
  // 计算每一个坐标
  float baseX = 0;  
  float baseY = 100;  
  float topY = baseY + fontMetrics.top;  
  float ascentY = baseY + fontMetrics.ascent;  
  float descentY = baseY + fontMetrics.descent;  
  float bottomY = baseY + fontMetrics.bottom;  

下面是具体实现代码：

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.RectF;
import android.util.AttributeSet;
import android.view.View;

/**
 * Created  on 2016/3/13.
 */
public class SongTextView extends View {
    private int postIndex;
    private Paint mPaint;
    private int delta = 15;
    private float mTextHeight;
    private float mTextWidth;
    private String mText="梦 里 面 看 我 七 十 二 变";
    private PorterDuffXfermode xformode;
    public SongTextView(Context ctx)
    {
        this(ctx,null);
    }
    public SongTextView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public SongTextView(Context context,  AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }
    public void init()
    {
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        xformode = new PorterDuffXfermode(PorterDuff.Mode.SRC_IN);
        mPaint.setColor(Color.CYAN);
        mPaint.setTextSize(60.0f);
        mPaint.setStyle(Paint.Style.FILL_AND_STROKE);
        mPaint.setXfermode(null);
        mPaint.setTextAlign(Paint.Align.LEFT);
        //文字精确高度
        Paint.FontMetrics fontMetrics = mPaint.getFontMetrics();
        mTextHeight = fontMetrics.bottom-fontMetrics.descent-fontMetrics.ascent;
        mTextWidth  = mPaint.measureText(mText);
    }
    /**
      *计算 控件的宽高
      */
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
      final  int mWidth;
      final  int mHeight;
        /**
         * 设置宽度
         */
        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        int widthSize = MeasureSpec.getSize(widthMeasureSpec);
        if (widthMode == MeasureSpec.EXACTLY)// match_parent , accurate
            mWidth = widthSize;
        else
        {
            // 由图片决定的宽
            int desireByImg = getPaddingLeft() + getPaddingRight()
                    + getMeasuredWidth();
            if (widthMode == MeasureSpec.AT_MOST)// wrap_content
                mWidth = Math.min(desireByImg, widthSize);
             else
                mWidth = desireByImg;