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：

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;
        }
        /***
         * 设置高度
         */
        int   heightMode = MeasureSpec.getMode(heightMeasureSpec);
        int   heightSize = MeasureSpec.getSize(heightMeasureSpec);
        if (heightMode == MeasureSpec.EXACTLY)// match_parent , accurate
            mHeight = heightSize;
         else
        {
            int desire = getPaddingTop() + getPaddingBottom()
                    + getMeasuredHeight();
            if (heightMode == MeasureSpec.AT_MOST)// wrap_content
                mHeight = Math.min(desire, heightSize);
             else
                mHeight = desire;
        }
        setMeasuredDimension( mWidth,  mHeight);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        Bitmap srcBitmap = Bitmap.createBitmap(getMeasuredWidth(),getMeasuredHeight(), Bitmap.Config.ARGB_8888);
        Canvas srcCanvas = new Canvas(srcBitmap);
        srcCanvas.drawText(mText, 0, mTextHeight, mPaint);
        mPaint.setXfermode(xformode);
        mPaint.setColor(Color.RED);
        RectF rectF = new RectF(0,0,postIndex,getMeasuredHeight());
        srcCanvas.drawRect(rectF, mPaint);
        canvas.drawBitmap(srcBitmap, 0, 0, null);
        init();
        if(postIndex<mTextWidth)
        {
            postIndex+=10;
        }else{
            postIndex=0;
        }
        postInvalidateDelayed(30);
    }
}

ProgressBar实现歌词播放效果

然后接下来的这种歌词播放进度效果是2张图片实现的，忘记是哪个那里看来的，压根以前也没有想过还可以这么样的实现。
只需要准备2张图即可：

<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:id="@android:id/background"
        android:drawable="@drawable/normal" />
    <item
        android:id="@android:id/progress"
        android:drawable="@drawable/grandient" />
</layer-list>

看见没就是2张图片，一张作为背景图一张作为进度图，是不是感觉很神奇，然后放入ProgressBar

  <ProgressBar
        android:id="@+id/pb1"
        style="@android:style/Widget.ProgressBar.Horizontal"
        android:layout_width="300dp"
        android:layout_height="40dp"
        android:max="100"
        android:maxHeight="2dp"
        android:minHeight="2dp"
        android:progress="20"
     android:progressDrawable="@drawable/m_progress_horizontal"
        android:secondaryProgress="30"
      android:visibility="gone"/>

再加上代码动态改变progress就能实现进度的变化了：

 ProgressBar pb1= (ProgressBar) findViewById(R.id.pb1);
          //设置滚动条可见
        setProgressBarIndeterminateVisibility(true);
        progress=pb1.getProgress();//获取初始进度
        timer=new Timer();
        task=new TimerTask() {
            @Override
            public void run() {
                progress+=10;
                if(progress>100){
                    progress=0;
                }
                handler.sendEmptyMessage(0);
            }
        };
        timer.schedule(task,1000,300);

实现及进度的改变：

Handler handler=new Handler(){
    @Override
    public void handleMessage(Message msg) {
        super.handleMessage(msg);
        pb1.setProgress(progress);
    }
};

    @Override
    protected void onDestroy() {
        super.onDestroy();
        timer=null;
        task=null;
        handler.removeCallbacksAndMessages(null);
    }

效果也是不错的：

能力有限，感觉写一篇博客要弄好久，网速卡的一笔，就写到这了，其实项目里面也没有用到，休息2天了也写点东西，就觉得还是要学一点东西作为备用知识。

demo可下载：TextViewGradient.rar
接下来都会去写一下文字特效的，下一篇我们就来实现仿京东垂直新闻栏