为了有更好的UI体验,一般我们会把button、textview等控件的背景设置上阴影。传统的做法是美工提供一张具有阴影效果的nine patch图,然后将其在xml文件中添加到background属性。这种做法没有问题,不过缺乏灵活性。
图1.使用代码生成的具有“阴影”效果的控件
在android中,每一种在xml文件中定义的图片,均可以使用java代码生成,其中LayerDrawable对应的xml文件的根元素为<layer-list>。
首先我介绍一下使用xml文件生成“阴影”背景效果图片:
<?xml version= "1.0" encoding ="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" > <item >
<shape android:shape="rectangle" >
<solid android:color="#ffbbbbbb" /> <corners android:radius="2dp" /> </shape>
</item > <item
android:bottom="1px"
android:right="1px" >
<shape android:shape="rectangle" >
<solid android:color="#ffdddddd" /> <corners android:radius="2dp" /> <padding
android:bottom="10dp"
android:left="10dp"
android:right="10dp"
android:top="10dp" />
</shape>
</item > </layer-list>
解析:
1.shape元素生成ShapeDrawable对象,不过需要注意的是,xml中虽然指明生成"rectangle"类型的对象,但如果想要在java中生成的rectangle具有圆角,那么java中对应的shape应该是RoundRectShape。
2.solid元素指明背景颜色,且paint的style为fill。
3.第二个元素android:bottom等代表的是LayerDrawable中第二个drawable相对于第一个drawable的inset,对应的java代码为:
layerDrawable.setLayerInset(1, 0, 0, 1, 1);
源码为:
/** Specify modifiers to the bounds for the drawable[index].
left += l
top += t;
right -= r;
bottom -= b;
*/
public void setLayerInset(int index, int l, int t, int r, int b) {
ChildDrawable childDrawable = mLayerState.mChildren[index];
childDrawable.mInsetL = l;
childDrawable.mInsetT = t;
childDrawable.mInsetR = r;
childDrawable.mInsetB = b;
}
可以看出setLayerInset()函数的作用就是将某层(层数从0开始计数)相对于上一层进行向里偏移。当然如果传入的数值为负数,就是向外偏移了,不过这时上层就遮挡住下层了,失去了使用layer的意义了。
4.padding的作用同样非常重要:
(1)当在最上层使用padding时,它指明的是最上层的drawable边缘与内容之间的padding;
(2)当在非最上层使用padding时,它指明当前层与上层之间的padding。
下面使用java代码生成LayerDrawable。
private void setLayerBg(View view){ int radius0 = 10;
float[] outerR = new float[] { radius0, radius0, radius0, radius0, radius0, radius0, radius0, radius0 };
RoundRectShape roundRectShape0 = new RoundRectShape(outerR, null, null); int radius1 = 10;
float[] outerR1 = new float[] { radius1, radius1, radius1, radius1, radius1, radius1, radius1, radius1 };
RoundRectShape roundRectShape1 = new RoundRectShape(outerR1, null, null); ShapeDrawable shapeDrawableBg = new ShapeDrawable(); shapeDrawableBg.setPadding(0, 0, 0, 0);
shapeDrawableBg.setShape(roundRectShape0); shapeDrawableBg.getPaint().setStyle(Paint.Style.FILL);
shapeDrawableBg.getPaint().setColor(0xffbbbbbb); ShapeDrawable shapeDrawableFg = new ShapeDrawable(); shapeDrawableFg.setPadding(23, 23, 23, 23);
shapeDrawableFg.setShape(roundRectShape1); shapeDrawableFg.getPaint().setStyle(Paint.Style.FILL);
shapeDrawableFg.getPaint().setColor(0xffdddddd); Drawable[] layers = {shapeDrawableBg, shapeDrawableFg};
LayerDrawable layerDrawable = new LayerDrawable(layers);
layerDrawable.setLayerInset(1, 0, 0, 1, 1); view.setBackgroundDrawable(layerDrawable); }
注释我就不写了,具体的解释见上面的解析。
LayerDrawable和StateListDrawable相结合使用
当我们遇到可点击的控件时,需要给此控件自定义几个不同状态的background,比如按下效果、普通状态效果,这时就需要用到StateListDrawable。
采用LayerDrawable生成的图片具有的只是静态属性,当将不同状态的LayerDrawable添加到一个StateListDrawable中,这样控件不同状态时均选择是否具有阴影效果。
代码如下:
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main); text = (TextView)this.findViewById(R.id.text);
text.setBackgroundDrawable(getStateListDrawable());
text.setOnClickListener(new View.OnClickListener() { @Override
public void onClick(View v) {
Toast.makeText(getApplicationContext(), "ttt", Toast.LENGTH_SHORT).show();
}
});
} private Drawable getStateListDrawable(){ StateListDrawable stateListDrawable = new StateListDrawable(); int[] stateHighlighted = new int[]{android.R.attr.state_pressed};
Drawable highlightedDrawable = getLayerDrawable(0xffcccccc);
stateListDrawable.addState(stateHighlighted, highlightedDrawable); int[] stateNormal = new int[]{};
Drawable normalDrawable = getLayerDrawable(0xffdddddd);
stateListDrawable.addState(stateNormal, normalDrawable); return stateListDrawable;
} private Drawable getLayerDrawable(int foregroundColor){ int radius0 = 10;
float[] outerR = new float[] { radius0, radius0, radius0, radius0, radius0, radius0, radius0, radius0 };
RoundRectShape roundRectShape0 = new RoundRectShape(outerR, null, null); int radius1 = 10;
float[] outerR1 = new float[] { radius1, radius1, radius1, radius1, radius1, radius1, radius1, radius1 };
RoundRectShape roundRectShape1 = new RoundRectShape(outerR1, null, null); ShapeDrawable shapeDrawableBg = new ShapeDrawable();
shapeDrawableBg.setPadding(0, 0, 0, 0);
shapeDrawableBg.setShape(roundRectShape0);
shapeDrawableBg.getPaint().setStyle(Paint.Style.FILL);
shapeDrawableBg.getPaint().setColor(0xffbbbbbb); ShapeDrawable shapeDrawableFg = new ShapeDrawable();
shapeDrawableFg.setPadding(23, 23, 23, 23);
shapeDrawableFg.setShape(roundRectShape1);
shapeDrawableFg.getPaint().setStyle(Paint.Style.FILL);
shapeDrawableFg.getPaint().setColor(foregroundColor); Drawable[] layers = {shapeDrawableBg, shapeDrawableFg};
LayerDrawable layerDrawable = new LayerDrawable(layers);
layerDrawable.setLayerInset(1, 0, 0, 1, 1); return layerDrawable;
}
需要注意的是:当给View、TextView、ImageView、ViewGroup等类型的默认没有按下事件的控件添加StateListDrawable时,控件需要设置上click事件,否则按下效果不起作用
备注:
这里只是通过两幅颜色单一的drawable错位简单的生成“阴影效果”,后续可以通过shader等效果,生成逐渐淡出的“阴影”效果。
使用xml定义layer-list的示例:
使用layer-list定义的xml作为button的背景。其中:
Button1:
1.底部drawable没有设置padding
2.顶部drawable没有设置padding
3.顶部drawable设置inset为5px
android:left="5px"
android:top="5px"
android:bottom="5px"
android:right="5px"
button1背景的完整xml:
<?xml version= "1.0" encoding ="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" > <item >
<shape android:shape="rectangle" >
<solid android:color="#ff00ff00" /> <corners android:radius="3dp" /> </shape>
</item > <item
android:left="5px"
android:top="5px"
android:bottom="5px"
android:right="5px" >
<shape android:shape="rectangle" >
<solid android:color="#ffff0000" /> <corners android:radius="3dp" /> </shape>
</item > </layer-list>
Button2:
1.底部drawable没有设置padding
2.顶部drawable设置inset均为5px
android:left="5px"
android:top="5px"
android:bottom="5px"
android:right="5px"
3.顶部drawable设置padding均为50dp
<padding
android:bottom="50dp"
android:left="50dp"
android:right="50dp"
android:top="50dp" />
button2背景的完整xml:
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" >
<!-- Z-Order 底部drawable -->
<item >
<shape android:shape="rectangle" >
<solid android:color="#ff00ff00" /> <corners android:radius="3dp" /> </shape>
</item > <!-- 顶部drawable -->
<item
android:left="5px"
android:top="5px"
android:bottom="5px"
android:right="5px" >
<shape android:shape="rectangle" >
<solid android:color="#ffff0000" /> <corners android:radius="3dp" /> <padding
android:bottom="50dp"
android:left="50dp"
android:right="50dp"
android:top="50dp" />
</shape>
</item > </layer-list>
Button3:
1.底部drawable设置padding均为20dp
2.顶部drawable没有设置inset
3.顶部drawable设置padding均为50dp
<padding
android:bottom="50dp"
android:left="50dp"
android:right="50dp"
android:top="50dp" />
button3背景的完整xml:
<?xml version= "1.0" encoding ="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" > <item>
<shape android:shape="rectangle" >
<solid android:color="#ff00ff00" /> <corners android:radius="3dp" /> <padding
android:bottom="20dp"
android:left="20dp"
android:right="20dp"
android:top="20dp" />
</shape>
</item> <item>
<shape android:shape="rectangle" >
<solid android:color="#ffff0000" /> <corners android:radius="3dp" /> <padding
android:bottom="50dp"
android:left="50dp"
android:right="50dp"
android:top="50dp" />
</shape>
</item> </layer-list>