Android -- selector&&StateListDrawable

<?xml version="1.0" encoding="utf-8" ?>     
<selector xmlns:android="http://schemas.android.com/apk/res/android">   
  <!-- 触摸时并且当前窗口处于交互状态 -->    
  <item android:state_pressed="true" android:state_window_focused="true" android:drawable= "@drawable/pic1" />  
  <!--  触摸时并且没有获得焦点状态 -->    
  <item android:state_pressed="true" android:state_focused="false" android:drawable="@drawable/pic2" />    
  <!--选中时的图片背景-->    
  <item android:state_selected="true" android:drawable="@drawable/pic3" />     
  <!--获得焦点时的图片背景-->    
  <item android:state_focused="true" android:drawable="@drawable/pic4" />    
  <!-- 窗口没有处于交互时的背景图片 -->    
  <item android:drawable="@drawable/pic5" />   
</selector>

public void addState (int[] stateSet, Drawable drawable)

//初始化一个空对象  
StateListDrawable stalistDrawable = new StateListDrawable();  
//获取对应的属性值 Android框架自带的属性 attr  
int pressed = android.R.attr.state_pressed;  
int window_focused = android.R.attr.state_window_focused;  
int focused = android.R.attr.state_focused;  
int selected = android.R.attr.state_selected;  
  
stalistDrawable.addState(new int []{pressed , window_focused}, getResources().getDrawable(R.drawable.pic1));  
stalistDrawable.addState(new int []{pressed , -focused}, getResources().getDrawable(R.drawable.pic2);  
stalistDrawable.addState(new int []{selected }, getResources().getDrawable(R.drawable.pic3);  
stalistDrawable.addState(new int []{focused }, getResources().getDrawable(R.drawable.pic4);  
//没有任何状态时显示的图片，我们给它设置我空集合  
stalistDrawable.addState(new int []{}, getResources().getDrawable(R.drawable.pic5);

public boolean isStateful ()

//主要功能是根据当前的状态值去更换对应的背景Drawable对象  
    public void refreshDrawableState() {  
        mPrivateFlags |= DRAWABLE_STATE_DIRTY;  
        //所有功能在这个函数里去完成  
        drawableStateChanged();  
        //...  
    }  

    // 获得当前的状态属性--- 整型集合 ； 调用Drawable类的setState方法去获取资源。  
    protected void drawableStateChanged() {  
        //该视图对应的Drawable对象，通常对应于StateListDrawable类对象  
        Drawable d = mBGDrawable;     
        if (d != null && d.isStateful()) {  //通常都是成立的  
            //getDrawableState()方法主要功能：会根据当前View的状态属性值，将其转换为一个整型集合  
            //setState()方法主要功能：根据当前的获取到的状态，更新对应状态下的Drawable对象。  
            d.setState(getDrawableState());  
        }  
    }  

    public final int[] getDrawableState() {  
        if ((mDrawableState != null) && ((mPrivateFlags & DRAWABLE_STATE_DIRTY) == 0)) {  
            return mDrawableState;  
        } else {  
            //根据当前View的状态属性值，将其转换为一个整型集合，并返回  
            mDrawableState = onCreateDrawableState(0);  
            mPrivateFlags &= ~DRAWABLE_STATE_DIRTY;  
            return mDrawableState;  
        }  
    }

//如果状态态值发生了改变，就回调onStateChange()方法。  
public boolean setState(final int[] stateSet) {  
    if (!Arrays.equals(mStateSet, stateSet)) {  
        mStateSet = stateSet;  
        return onStateChange(stateSet);  
    }  
    return false;  
}

//状态值发生了改变，我们需要找出第一个吻合的当前状态的Drawable对象  
protected boolean onStateChange(int[] stateSet) {  
    //要找出第一个吻合的当前状态的Drawable对象所在的索引位置， 具体匹配算法请自己深入源码看看  
    int idx = mStateListState.indexOfStateSet(stateSet);  
    ...  
    //获取对应索引位置的Drawable对象  
    if (selectDrawable(idx)) {  
        return true;  
    }  
    ...  
}

public boolean selectDrawable(int idx)  
{  
    if (idx >= 0 && idx < mDrawableContainerState.mNumChildren) {  
        //获取对应索引位置的Drawable对象  
        Drawable d = mDrawableContainerState.mDrawables[idx];  
        ...  
        mCurrDrawable = d; //mCurrDrawable即使当前Drawable对象  
        mCurIndex = idx;  
        ...  
    } else {  
       ...  
    }  
    //请求该View刷新自己,这个方法我们稍后讲解。  
    invalidateSelf();  
    return true;  
}

public static interface Callback {  
    //如果Drawable对象的状态发生了变化，会请求View重新绘制，  
    //因此我们对应于该View的背景Drawable对象能够”绘制出来”.  
    public void invalidateDrawable(Drawable who); 
 
    public void scheduleDrawable(Drawable who, Runnable what, long when);   
    public void unscheduleDrawable(Drawable who, Runnable what);  
}

public class View implements Drawable.Callback, KeyEvent.Callback, AccessibilityEventSource   
{  
    ...  
    //Invalidates the specified Drawable.  
    //默认实现，重新绘制该视图本身  
    public void invalidateDrawable(Drawable drawable) {  
        if (verifyDrawable(drawable)) { //是否是同一个Drawable对象，通常为真  
            final Rect dirty = drawable.getBounds();  
            final int scrollX = mScrollX;  
            final int scrollY = mScrollY;  
            //重新请求绘制该View，即重新调用该View的draw()方法  ...  
            invalidate(dirty.left + scrollX, dirty.top + scrollY,  
                    dirty.right + scrollX, dirty.bottom + scrollY);  
        }  
    }  
    ...  
}

Drawable d  ;                // 图片资源                        
d.setCallback(View v) ;  // 视图v的背景资源为 d 对象