Android渐变研究

效果图如下：

上面的例子中我们在gradient标签中设置了startColor，endColor，angle用来表示开始结束的颜色和变化方向。 gradient标签的所有属性说明如下：

android:angle：（Integer） 渐变的角度，线性渐变时才有效，必须是45的倍数，0表示从左到右，90表示从下到上

android:centerX：（Float）渐变中心的相对X坐标，放射渐变时才有效，在0.0到1.0之间，默认为0.5，表示在正中间

android:centerY：（Float）渐变中心的相对X坐标，放射渐变时才有效，在0.0到1.0之间，默认为0.5，表示在正中间

android:centerColor ：（Color）中间点的色值

android:endColor ： （Color）结束的色值

android:startColor：（Color）开始的色值。

android:gradientRadius：（Float）渐变的半径，只有在android:type="radial"的时候有效。

android:type ：有三种类型 "linear" 线性渐变， "radial" 放射渐变，设置该项时，android:gradientRadius也必须设置 "sweep" 扫描性渐变

android:useLevel ： 如果为true，将被当成LevelListDrawable使用。

除了用xml设置，还可以在编码中设置， 标签对应的类是GradientDrawable，GradientDrawable是Drawable的子类。 代码如下：

public class TestActivity extends Activity {        @Override      protected void onCreate(Bundle savedInstanceState) {          super.onCreate(savedInstanceState);          setContentView(new SampleView(this));      }        private static class SampleView extends View {          private Rect mRect;          private GradientDrawable mDrawable;            public SampleView(Context context) {              super(context);              setFocusable(true);                mRect = new Rect(0, 0, 300, 300);              mDrawable = new GradientDrawable(GradientDrawable.Orientation.TL_BR,                      new int[] { 0xaa000000,                              0xFFFFFFFF });              mDrawable.setShape(GradientDrawable.RECTANGLE);              mDrawable.setGradientRadius((float)(Math.sqrt(2) * 60));          }            static void setCornerRadii(GradientDrawable drawable, float r0,                                     float r1, float r2, float r3) {              drawable.setCornerRadii(new float[] { r0, r0, r1, r1,                      r2, r2, r3, r3 });          }            @Override protected void onDraw(Canvas canvas) {                mDrawable.setBounds(mRect);                float r = 16;                canvas.save();              canvas.translate(10, 10);              mDrawable.setGradientType(GradientDrawable.LINEAR_GRADIENT);              setCornerRadii(mDrawable, r, r, 0, 0);              mDrawable.draw(canvas);              canvas.restore();                canvas.save();              canvas.translate(10 + mRect.width() + 10, 10);              mDrawable.setGradientType(GradientDrawable.RADIAL_GRADIENT);              setCornerRadii(mDrawable, 0, 0, r, r);              mDrawable.draw(canvas);              canvas.restore();                canvas.translate(0, mRect.height() + 10);                canvas.save();              canvas.translate(10, 10);              mDrawable.setGradientType(GradientDrawable.SWEEP_GRADIENT);              setCornerRadii(mDrawable, 0, r, r, 0);              mDrawable.draw(canvas);              canvas.restore();            }      }  }

public GradientDrawable(Orientation orientation, int[] colors) {          this(new GradientState(orientation, colors));      }

public enum Orientation {          /** draw the gradient from the top to the bottom */          TOP_BOTTOM,          /** draw the gradient from the top-right to the bottom-left */          TR_BL,          /** draw the gradient from the right to the left */          RIGHT_LEFT,          /** draw the gradient from the bottom-right to the top-left */          BR_TL,          /** draw the gradient from the bottom to the top */          BOTTOM_TOP,          /** draw the gradient from the bottom-left to the top-right */          BL_TR,          /** draw the gradient from the left to the right */          LEFT_RIGHT,          /** draw the gradient from the top-left to the bottom-right */          TL_BR,      }

Paint shaderPaint = new Paint();        shaderPaint.setShader(myLinearGradient);

public class TestActivity extends Activity {                        @Override              protected void onCreate(Bundle savedInstanceState) {                  super.onCreate(savedInstanceState);                  setContentView(new SampleView(this));              }                        private static class SampleView extends View {                  private Paint mPaint;                  private Rect mRect;                  LinearGradient lg1 ;                  LinearGradient lg2 ;                  LinearGradient lg3 ;                            public SampleView(Context context) {                      super(context);                      setFocusable(true);                                mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);                      mRect = new Rect(0, 0, 300, 300);                                 lg1 = new LinearGradient(0,0,150,150, Color.TRANSPARENT,Color.BLACK,                              Shader.TileMode.MIRROR);                       lg2 = new LinearGradient(0,0,150,150, Color.TRANSPARENT,Color.BLACK,                              Shader.TileMode.CLAMP);                       lg3 = new LinearGradient(0,0,150,150, Color.TRANSPARENT,Color.BLACK,                              Shader.TileMode.REPEAT);                            }                            @Override protected void onDraw(Canvas canvas) {                      canvas.save();                      canvas.translate(10, 10);                      mPaint.setShader(lg1) ;                      canvas.drawRect(mRect,mPaint);                      canvas.restore();                                canvas.save();                      canvas.translate(10 + mRect.width() + 10, 10);                      mPaint.setShader(lg2) ;                      canvas.drawRect(mRect,mPaint);                      canvas.restore();                                canvas.save();                      canvas.translate(10,10 + mRect.height() + 10);                      mPaint.setShader(lg3) ;                      canvas.drawRect(mRect,mPaint);                      canvas.restore();                  }              }          }

LinearGradient(float x0, float y0, float x1, float y1, int[] colors, float[] positions, Shader.TileMode tile)  LinearGradient(float x0, float y0, float x1, float y1, int color0, int color1, Shader.TileMode tile)

public class TestActivity extends Activity  {                  @Override           protected void onCreate(Bundle savedInstanceState) {               super.onCreate(savedInstanceState);               setContentView(R.layout.activity_test);                      if(Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.JELLY_BEAN) {                   View bottom = findViewById(R.id.layout_bottom);                   bottom.setBackground(                           ScrimUtil.makeCubicGradientScrimDrawable(                                   0xaa000000, //颜色                                   8, //渐变层数                                   Gravity.BOTTOM)); //起始方向               }           }              }

public class ScrimUtil {        private ScrimUtil() {      }        /**       * Creates an approximated cubic gradient using a multi-stop linear gradient. See       * <a href="https://plus.google.com/+RomanNurik/posts/2QvHVFWrHZf">this post</a> for more       * details.       */      public static Drawable makeCubicGradientScrimDrawable(int baseColor, int numStops, int gravity) {          numStops = Math.max(numStops, 2);            PaintDrawable paintDrawable = new PaintDrawable();          paintDrawable.setShape(new RectShape());            final int[] stopColors = new int[numStops];            int red = Color.red(baseColor);          int green = Color.green(baseColor);          int blue = Color.blue(baseColor);          int alpha = Color.alpha(baseColor);            for (int i = 0; i < numStops; i++) {              float x = i * 1f / (numStops - 1);              float opacity = constrain(0, 1, (float) Math.pow(x, 3));              stopColors[i] = Color.argb((int) (alpha * opacity), red, green, blue);          }            final float x0, x1, y0, y1;          switch (gravity & Gravity.HORIZONTAL_GRAVITY_MASK) {              case Gravity.LEFT:  x0 = 1; x1 = 0; break;              case Gravity.RIGHT: x0 = 0; x1 = 1; break;              default:            x0 = 0; x1 = 0; break;          }          switch (gravity & Gravity.VERTICAL_GRAVITY_MASK) {              case Gravity.TOP:    y0 = 1; y1 = 0; break;              case Gravity.BOTTOM: y0 = 0; y1 = 1; break;              default:             y0 = 0; y1 = 0; break;          }            paintDrawable.setShaderFactory(new ShapeDrawable.ShaderFactory() {              @Override              public Shader resize(int width, int height) {                  LinearGradient linearGradient = new LinearGradient(                          width * x0,                          height * y0,                          width * x1,                          height * y1,                          stopColors, null,                          Shader.TileMode.CLAMP);                  return linearGradient;              }          });            return paintDrawable;      }        private  static float constrain(float min, float max, float v) {          return Math.max(min, Math.min(max, v));      }  }

public class TestLayout extends View {        public TestLayout(Context context) {          super(context);          init(null, 0);      }      public TestLayout(Context context, AttributeSet attrs) {          super(context, attrs);          init(attrs, 0);      }      public TestLayout(Context context, AttributeSet attrs, int defStyle) {          super(context, attrs, defStyle);          init(attrs, defStyle);      }        @SuppressWarnings("deprecation")      private void init(AttributeSet attrs, int defStyle) {      }          /**       * =============================================================================================       * The Animator methods       * =============================================================================================       */      /**       * 开始背景动画（此处为属性动画）       */      void startBackgroundAnimator(){          /*           *参数解释：           *target：设置属性动画的目标类，此处是当前自定义view所以使用this           *propertyName:属性名称。（要对View的那个属性执行动画操作）           *values数组：根据时间的推移动画将根据数组的内容进行改变           */          ValueAnimator anim = ObjectAnimator.ofInt(this, "backgroundColor", Color.RED,Color.BLUE,Color.GRAY,Color.GREEN);          //动画持续时间为3秒          anim.setDuration(3000);          /*           * ArgbEvaluator：这种评估者可以用来执行类型之间的插值整数值代表ARGB颜色。           * FloatEvaluator：这种评估者可以用来执行浮点值之间的插值。           * IntEvaluator：这种评估者可以用来执行类型int值之间的插值。           * RectEvaluator：这种评估者可以用来执行类型之间的插值矩形值。           *           * 由于本例是改变View的backgroundColor属性的背景颜色所以此处使用ArgbEvaluator           */          anim.setEvaluator(new ArgbEvaluator());          //设置动画重复次数，此处设置无限重复          anim.setRepeatCount(ValueAnimator.INFINITE);          //设置重复模式          anim.setRepeatMode(ValueAnimator.REVERSE);          //开启动画          anim.start();      }  }

<RelativeLayout                xmlns:android="http://schemas.android.com/apk/res/android"                xmlns:tools="http://schemas.android.com/tools"                android:layout_width="match_parent"                android:layout_height="match_parent"                >                            <com.mxn.soul.demo.TestLayout                    android:id="@+id/layout_bottom"                    android:layout_width="match_parent"                    android:layout_height="300dp"                    android:layout_alignParentBottom="true"                    android:orientation="horizontal"                    />                        </RelativeLayout>

public class TestActivity extends Activity  {        @Override      protected void onCreate(Bundle savedInstanceState) {          super.onCreate(savedInstanceState);          setContentView(R.layout.activity_test);            TestLayout bottom = (TestLayout) findViewById(R.id.layout_bottom);          bottom.startBackgroundAnimator() ;      }    }