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