原创--解剖android Style原理从Button入手

转载声明原处:博客http://pk272205020.blog.163.com/

参考论坛外国android论坛http://www.androidpeople.com/

参考资料：androidButton原理

这几日都是看androidSDK原码,想封装一个HERO效果的UI界面。刚想以为很容易，但越做越难，为有百度，Google求救,但这方面的资料还是不多,这个我也不怪了,可能android在中国的市场还是刚刚起步。外面的一些网站android技术论坛打不开,闷...

但我发现http://www.android.com/可以打开了,以前要用XX软件先打得开,但里面的developer标签还是俾中国网关封,这个更郁闷...不讲了,直入正题androidStyel原理

刚刚开始得写时从最简单的Button入手,下载SDK原码候Button继续TextView原码里就三个构造方法....

@RemoteView
public class Button extends TextView {
    public Button(Context context) {
        this(context, null);
    }

    public Button(Context context, AttributeSet attrs) {
        this(context, attrs, com.android.internal.R.attr.buttonStyle);
    }

    public Button(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }
}[

默认样式:com.android.internal.R.attr.buttonStyle,android的style太强大,网上有人说过是GWT模式,在校的时候我也用过GWT写过小网页,HTML文件里标签里嵌入GWT标签,通过服务端Java代码生成页面，GWT就讲到这里，有开展过GWT的同志就知道这个也很像android的Layout布局文件,哈哈我也是认同网上的人说。

知道android的Style模式后,我们要进一步了解内部的实现，我们要打开com.android.internal.R.attr.buttonStyle这个对应的XML

< style name="Widget.Button" >

< item name="android:background">@android:drawable/btn_default< /item>

< item name="android:focusable" >true< /item >

< item name="android:clickable" >true< /item >

< item name="android:textSize" >20sp< /item >

< item name="android:textStyle" >normal< /item >

< item name="android:textColor" >@android:color/button_text </item > 

< itemname="android:gravity">center_vertical|center_horizontal< /item>

< /style >

这个文件定义了好多style相关的属性，每个属性都好理解，这个backgroud属性难道仅仅是一个drawable图片?如果仅仅是一个图片的化，怎么能够实现button各种状态下表现出不同背景的功能呢?还是来看看这个drawable到底是什么东西。

还是埋头苦干地找出答案

在drwable目录中发现这个btn_default这个文件，还有许多这样的xml文件，看名字可以估到是什么来的

btn_default.xml内容

< selector xmlns:android="http://schemas.android.com/apk/res/android">

< item android:state_window_focused="false" android:state_enabled="true"
android:drawable="@drawable/btn_default_normal" / >

 < item android:state_window_focused="false" android:state_enabled="false"
android:drawable="@drawable/btn_default_normal_disable" / >

< item android:state_pressed="true"
android:drawable="@drawable/btn_default_pressed" / >

< item android:state_focused="true" android:state_enabled="true"
android:drawable="@drawable/btn_default_selected" / >

< item android:state_enabled="true"
android:drawable="@drawable/btn_default_normal" / >

< item android:state_focused="true"
android:drawable="@drawable/btn_default_normal_disable_focused" / >

< item android:drawable="@drawable/btn_default_normal_disable" / >

< /selector >

在android中drawable文件是看图片存放的，最普通的就是一个图片。而这里用到的是StateListDrawable。当Android的解析器解析到上面的xml时，会自动转化成一个StateListDrawable类的实例，看看SDK是这样说的

LetsyouassignanumberofgraphicimagestoasingleDrawableandswapoutthevisibleitembyastringIDvalue.

ItcanbedefinedinanXMLfilewiththe<selector>element.EachstateDrawableisdefinedinanested<item>element.Formoreinformation,seetheguidetoDrawableResources.

意思就是通过字符串标识符值ID分配单个可绘制可切换的可视图形项

看看核心代码吧：大部多代码删除了

public class StateListDrawable extends DrawableContainer {
/**
* To be proper, we should have a getter for dither (and alpha, etc.)
* so that proxy classes like this can save/restore their delegates'
* values, but we don't have getters. Since we do have setters
* (e.g. setDither), which this proxy forwards on, we have to have some
* default/initial setting.
*
* The initial setting for dither is now true, since it almost always seems
* to improve the quality at negligible cost.
*/
private static final boolean DEFAULT_DITHER = true;
private final StateListState mStateListState;
private boolean mMutated;

public StateListDrawable() {
this(null, null);
}

/**
* Add a new image/string ID to the set of images.
*
* @param stateSet - An array of resource Ids to associate with the image.
* Switch to this image by calling setState().
* @param drawable -The image to show.
*/
public void addState(int[] stateSet, Drawable drawable) {
if (drawable != null) {
mStateListState.addStateSet(stateSet, drawable);
// in case the new state matches our current state...
onStateChange(getState());
}
}

@Override
public boolean isStateful() {
return true;
}

@Override
protected boolean onStateChange(int[] stateSet) {
int idx = mStateListState.indexOfStateSet(stateSet);
if (idx < 0) {
idx = mStateListState.indexOfStateSet(StateSet.WILD_CARD);
}
if (selectDrawable(idx)) {
return true;
}
return super.onStateChange(stateSet);
}


/**
* Gets the state set at an index.
*
* @param index The index of the state set.
* @return The state set at the index.
* @hide pending API council
* @see #getStateCount()
* @see #getStateDrawable(int)
*/
public int[] getStateSet(int index) {
return mStateListState.mStateSets[index];
}


static final class StateListState extends DrawableContainerState {
private int[][] mStateSets;

StateListState(StateListState orig, StateListDrawable owner, Resources res) {
super(orig, owner, res);

if (orig != null) {
mStateSets = orig.mStateSets;
} else {
mStateSets = new int[getChildren().length][];
}
}


 

 int addStateSet(int[] stateSet, Drawable drawable) {
            final int pos = addChild(drawable);
            mStateSets[pos] = stateSet;
            return pos;
        }


}

private StateListDrawable(StateListState state, Resources res) {
StateListState as = new StateListState(state, this, res);
mStateListState = as;
setConstantState(as);
onStateChange(getState());
}
}

xml中每一个Item就对应一种状态，而每一个有state_的属性就是描述状态，drawable则是真正的drawable图片。当把这个实例付给View作为Background的时候，View会根据不同的state来切换不同状态的图片，从而实现了Press等诸多效果。简单看一下View中有关状态切换的代码吧：

/**
* The order here is very important to {@link #getDrawableState()}
*/
private static final int[][] VIEW_STATE_SETS = {
EMPTY_STATE_SET, // 0 0 0 0 0
WINDOW_FOCUSED_STATE_SET, // 0 0 0 0 1
SELECTED_STATE_SET, // 0 0 0 1 0
SELECTED_WINDOW_FOCUSED_STATE_SET, // 0 0 0 1 1
FOCUSED_STATE_SET, // 0 0 1 0 0
FOCUSED_WINDOW_FOCUSED_STATE_SET, // 0 0 1 0 1
FOCUSED_SELECTED_STATE_SET, // 0 0 1 1 0
FOCUSED_SELECTED_WINDOW_FOCUSED_STATE_SET, // 0 0 1 1 1
ENABLED_STATE_SET, // 0 1 0 0 0
ENABLED_WINDOW_FOCUSED_STATE_SET, // 0 1 0 0 1
ENABLED_SELECTED_STATE_SET, // 0 1 0 1 0
ENABLED_SELECTED_WINDOW_FOCUSED_STATE_SET, // 0 1 0 1 1
ENABLED_FOCUSED_STATE_SET, // 0 1 1 0 0
ENABLED_FOCUSED_WINDOW_FOCUSED_STATE_SET, // 0 1 1 0 1
ENABLED_FOCUSED_SELECTED_STATE_SET, // 0 1 1 1 0
ENABLED_FOCUSED_SELECTED_WINDOW_FOCUSED_STATE_SET, // 0 1 1 1 1
PRESSED_STATE_SET, // 1 0 0 0 0
PRESSED_WINDOW_FOCUSED_STATE_SET, // 1 0 0 0 1
PRESSED_SELECTED_STATE_SET, // 1 0 0 1 0
PRESSED_SELECTED_WINDOW_FOCUSED_STATE_SET, // 1 0 0 1 1
PRESSED_FOCUSED_STATE_SET, // 1 0 1 0 0
PRESSED_FOCUSED_WINDOW_FOCUSED_STATE_SET, // 1 0 1 0 1
PRESSED_FOCUSED_SELECTED_STATE_SET, // 1 0 1 1 0
PRESSED_FOCUSED_SELECTED_WINDOW_FOCUSED_STATE_SET, // 1 0 1 1 1
PRESSED_ENABLED_STATE_SET, // 1 1 0 0 0
PRESSED_ENABLED_WINDOW_FOCUSED_STATE_SET, // 1 1 0 0 1
PRESSED_ENABLED_SELECTED_STATE_SET, // 1 1 0 1 0
PRESSED_ENABLED_SELECTED_WINDOW_FOCUSED_STATE_SET, // 1 1 0 1 1
PRESSED_ENABLED_FOCUSED_STATE_SET, // 1 1 1 0 0
PRESSED_ENABLED_FOCUSED_WINDOW_FOCUSED_STATE_SET, // 1 1 1 0 1
PRESSED_ENABLED_FOCUSED_SELECTED_STATE_SET, // 1 1 1 1 0
PRESSED_ENABLED_FOCUSED_SELECTED_WINDOW_FOCUSED_STATE_SET, // 1 1 1 1 1
};

详细打开View.java自己看

下面是setBackground方法，红字就是是state切换，View这个类太长了，android2.2版一共9321行

/**
     * Set the background to a given Drawable, or remove the background. If the
     * background has padding, this View's padding is set to the background's
     * padding. However, when a background is removed, this View's padding isn't
     * touched. If setting the padding is desired, please use
     * {@link #setPadding(int, int, int, int)}.
     *
     * @param d The Drawable to use as the background, or null to remove the
     *        background
     */
    public void setBackgroundDrawable(Drawable d) {
        boolean requestLayout = false;

        mBackgroundResource = 0;

           ...............             

            if (d.isStateful()) {
                d.setState(getDrawableState());
            }
            d.setVisible(getVisibility() == VISIBLE, false);
            mBGDrawable = d;

           ...............

        mBackgroundSizeChanged = true;
        invalidate();
}

setBackgound方法先判断Drawable对象是否支持state切换如果支持，设置状态就可达到图片切换的效果。

就写到这里