Android GradientDrawable - Android 基础教程

GradientDrawable 是一个具有渐变区域的 Drawable，可以实现线性渐变,发散渐变和平铺渐变效果

GradientDrawable 的根节点是 <gradient>

GradientDrawable 属性

属性	说明
android:startColor	渐变的起始颜色
android:centerColor	渐变的中间颜色
android:endColor	渐变的结束颜色
android:type	渐变类型,可选值有 linear 线性渐变(可设置渐变角度) radial 发散渐变(中间向四周发散) sweep 平铺渐变
android:centerX	渐变中间颜色的 X 坐标,取值范围为: 0~1
android:centerY	渐变中间颜色的 Y 坐标,取值范围为: 0~1
android:angle	只有 linear 类型的渐变才有效,表示渐变角度,必须为 45 的倍数
android:gradientRadius	只有 radial 和 sweep 类型的渐变才有效, radial必须设置,表示渐变效果的半径
android:useLevel	判断是否根据 level 绘制渐变效果

范例

创建一个空的 Android 项目 cn.twle.android.GradientDrawable

创建三个 GradientDrawable 资源

线性渐变 res/drawable/gradient_linear.xml

<?xml version="1.0" encoding="utf-8"?>
<shape
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="oval" >
    <gradient
        android:angle="90"
        android:centerColor="#FFEB82"
        android:endColor="#35B2DE"
        android:startColor="#DEACAB" />

    <stroke
        android:dashGap="5dip"
        android:dashWidth="4dip"
        android:width="3dip"
        android:color="#fff" />
</shape>

(发散渐变) res/drawable/gradient_radial.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:innerRadius="0dip"
    android:shape="ring"
    android:thickness="70dip"
    android:useLevel="false" >

    <gradient
        android:centerColor="#FFEB82"
        android:endColor="#35B2DE"
        android:gradientRadius="70"
        android:startColor="#DEACAB"
        android:type="radial"
        android:useLevel="false" />

</shape>

(平铺渐变) res/drawable/gradient_sweep.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:innerRadiusRatio="8"
    android:shape="ring"
    android:thicknessRatio="3"
    android:useLevel="false" >

    <gradient
        android:centerColor="#FFEB82"
        android:endColor="#35B2DE"
        android:startColor="#DEACAB"
        android:type="sweep"
        android:useLevel="false" />

</shape>

修改 activity_main.xml 使用三个渐变资源

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:layout_width="200dp"
        android:layout_height="100dp"
        android:background="@drawable/gradient_linear" />

    <TextView
        android:layout_width="200dp"
        android:layout_height="200dp"
        android:background="@drawable/gradient_radial" />

    <TextView
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:background="@drawable/gradient_sweep" />

</LinearLayout>

范例 2

如果要绘制复杂的渐变的话，只用 xml 文件不远远不足的，需要使用 Java 代码来完成

创建一个空的 Android 项目 cn.twle.android.GradientDrawableMore

修改 MainActivity.java

package cn.twle.android.gradientdrawablemore;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapShader;
import android.graphics.Canvas;
import android.graphics.ComposePathEffect;
import android.graphics.CornerPathEffect;
import android.graphics.DiscretePathEffect;
import android.graphics.LinearGradient;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.PathEffect;
import android.graphics.RectF;
import android.graphics.Shader;
import android.graphics.SweepGradient;
import android.graphics.drawable.Drawable;
import android.graphics.drawable.ShapeDrawable;
import android.graphics.drawable.shapes.ArcShape;
import android.graphics.drawable.shapes.OvalShape;
import android.graphics.drawable.shapes.PathShape;
import android.graphics.drawable.shapes.RectShape;
import android.graphics.drawable.shapes.RoundRectShape;
import android.graphics.drawable.shapes.Shape;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new SampleView(this));
    }

    private static class SampleView extends View {
        private ShapeDrawable[] mDrawables;

        private static Shader makeSweep() {
            return new SweepGradient(150, 25,
                    new int[] { 0xFFFF0000, 0xFF00FF00, 0xFF0000FF, 0xFFFF0000 },
                    null);
        }

        private static Shader makeLinear() {
            return new LinearGradient(0, 0, 50, 50,
                    new int[] { 0xFFFF0000, 0xFF00FF00, 0xFF0000FF },
                    null, Shader.TileMode.MIRROR);
        }

        private static Shader makeTiling() {
            int[] pixels = new int[] { 0xFFFF0000, 0xFF00FF00, 0xFF0000FF, 0};
            Bitmap bm = Bitmap.createBitmap(pixels, 2, 2,
                    Bitmap.Config.ARGB_8888);

            return new BitmapShader(bm, Shader.TileMode.REPEAT,
                    Shader.TileMode.REPEAT);
        }

        private static class MyShapeDrawable extends ShapeDrawable {
            private Paint mStrokePaint = new Paint(Paint.ANTI_ALIAS_FLAG);

            public MyShapeDrawable(Shape s) {
                super(s);
                mStrokePaint.setStyle(Paint.Style.STROKE);
            }

            public Paint getStrokePaint() {
                return mStrokePaint;
            }

            @Override protected void onDraw(Shape s, Canvas c, Paint p) {
                s.draw(c, p);
                s.draw(c, mStrokePaint);
            }
        }

        public SampleView(Context context) {
            super(context);
            setFocusable(true);

            float[] outerR = new float[] { 12, 12, 12, 12, 0, 0, 0, 0 };
            RectF inset = new RectF(6, 6, 6, 6);
            float[] innerR = new float[] { 12, 12, 0, 0, 12, 12, 0, 0 };

            Path path = new Path();
            path.moveTo(50, 0);
            path.lineTo(0, 50);
            path.lineTo(50, 100);
            path.lineTo(100, 50);
            path.close();

            mDrawables = new ShapeDrawable[7];
            mDrawables[0] = new ShapeDrawable(new RectShape());
            mDrawables[1] = new ShapeDrawable(new OvalShape());
            mDrawables[2] = new ShapeDrawable(new RoundRectShape(outerR, null,
                    null));
            mDrawables[3] = new ShapeDrawable(new RoundRectShape(outerR, inset,
                    null));
            mDrawables[4] = new ShapeDrawable(new RoundRectShape(outerR, inset,
                    innerR));
            mDrawables[5] = new ShapeDrawable(new PathShape(path, 100, 100));
            mDrawables[6] = new MyShapeDrawable(new ArcShape(45, -270));

            mDrawables[0].getPaint().setColor(0xFFFF0000);
            mDrawables[1].getPaint().setColor(0xFF00FF00);
            mDrawables[2].getPaint().setColor(0xFF0000FF);
            mDrawables[3].getPaint().setShader(makeSweep());
            mDrawables[4].getPaint().setShader(makeLinear());
            mDrawables[5].getPaint().setShader(makeTiling());
            mDrawables[6].getPaint().setColor(0x88FF8844);

            PathEffect pe = new DiscretePathEffect(10, 4);
            PathEffect pe2 = new CornerPathEffect(4);
            mDrawables[3].getPaint().setPathEffect(
                    new ComposePathEffect(pe2, pe));

            MyShapeDrawable msd = (MyShapeDrawable)mDrawables[6];
            msd.getStrokePaint().setStrokeWidth(4);
        }

        @Override protected void onDraw(Canvas canvas) {

            int x = 10;
            int y = 10;
            int width = 400;
            int height = 100;

            for (Drawable dr : mDrawables) {
                dr.setBounds(x, y, x + width, y + height);
                dr.draw(canvas);
                y += height + 5;
            }
        }
    }
}

ShapeDrawable 是对普通图形的包装;包括

ArcShape
OvalShape
PathShape
RectShape
RoundRectShape

PathEffect 则是路径特效,可以制作复杂的图形边框,包括

CornerPathEffect
DashPathEffect
DiscretePathEffect