如何监听CollapsingToolbarLayout的展开与折

自定义一个继承了 AppBarLayout.OnOffsetChangedListener的类

public abstract class AppBarStateChangeListener implements AppBarLayout.OnOffsetChangedListener {
 
    public enum State {
        EXPANDED,
        COLLAPSED,
        IDLE
    }
 
    private State mCurrentState = State.IDLE;
 
    @Override
    public final void onOffsetChanged(AppBarLayout appBarLayout, int i) {
        if (i == 0) {
            if (mCurrentState != State.EXPANDED) {
                onStateChanged(appBarLayout, State.EXPANDED);
            }
            mCurrentState = State.EXPANDED;
        } else if (Math.abs(i) >= appBarLayout.getTotalScrollRange()) {
            if (mCurrentState != State.COLLAPSED) {
                onStateChanged(appBarLayout, State.COLLAPSED);
            }
            mCurrentState = State.COLLAPSED;
        } else {
            if (mCurrentState != State.IDLE) {
                onStateChanged(appBarLayout, State.IDLE);
            }
            mCurrentState = State.IDLE;
        }
    }
 
    public abstract void onStateChanged(AppBarLayout appBarLayout, State state);
}

然后添加监听

mAppBarLayout.addOnOffsetChangedListener(new AppBarStateChangeListener() {
            @Override
            public void onStateChanged(AppBarLayout appBarLayout, State state) {
                Log.d("STATE", state.name());
                if( state == State.EXPANDED ) {
                    
                    //展开状态
                    
                }else if(state == State.COLLAPSED){
                    
                    //折叠状态
                     
                }else {
                
                    //中间状态
                
                }
            }
        });

原文地址：https://blog.csdn.net/qq_21265915/article/details/55002056