StateListDrawable、selector执行顺序分析

Android_Drawable

在selector或者StateListDrawable的从上到下按顺序优先匹配

分析源码

StateListDrawable.java

// 添加对应状态的Drawable时插入Container数组的最后
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
// 主动或者被动触发调用
protected boolean onStateChange(int[] stateSet) {
    final boolean changed = super.onStateChange(stateSet);
    int idx = mStateListState.indexOfStateSet(stateSet);
    // 都没有匹配到，则使用兜底方案        
    if (idx < 0) {
        idx = mStateListState.indexOfStateSet(StateSet.WILD_CARD);
    }
    return selectDrawable(idx) || changed;
}

StateListState

// 获取指定状态的索引
int indexOfStateSet(int[] stateSet) {
    final int[][] stateSets = mStateSets;
    final int N = getChildCount();
    for (int i = 0; i < N; i++) {
        if (StateSet.stateSetMatches(stateSets[i], stateSet)) {
            return i;
        }
    }
    return -1;
}

StateSet.java

/**
 * A state specification that will be matched by all StateSets.
 */
 public static final int[] WILD_CARD = new int[0];
 /**
  * A state set that does not contain any valid states.
  */
 public static final int[] NOTHING = new int[] { 0 };
 public static boolean stateSetMatches(int[] stateSpec, int[] stateSet) {
    // 这里优先匹配了
    if (stateSet == null) {
        return (stateSpec == null || isWildCard(stateSpec));
    }
    // 匹配指定的顺序，从上到下优先匹配
    // ...
 }