appbarlayout.addOnOffsetChangedListener失效问题

AppBarLayout: onOffsetChanged stops being called after multiple scrolls

问题描述:

Using the CheeseSquare demo, if you register with AppBarLayout as an OnOffsetChangedListener, then onOffsetChanged is only called for a limited time. After multiple scrolls up and down, the method is never called.

Expected - onOffsetChanged should be called consistently for all registered listeners whenever the offset of AppBarLayout changes.
To reproduce: include this method in CheeseDetailActivity:

@Override
protected void onStart() {
super.onStart();
AppBarLayout appBarLayout = (AppBarLayout) findViewById(R.id.appbar);
appBarLayout.addOnOffsetChangedListener(new AppBarLayout.OnOffsetChangedListener() {
@Override
public void onOffsetChanged(AppBarLayout appBarLayout, int verticalOffset) {
Log.d(“CheeseDetailActivity”, ” verticalOffset ” + verticalOffset);
```
    }
});
```
}

原因:
Your problem is that AppBarLayout uses WeakReference to keep track of the offsetChanged listeners, and as soon as a GC is due your listener is collected.

解决方式:

@Override
    protected void onStart() {
        super.onStart();
        AppBarLayout appBarLayout = (AppBarLayout) findViewById(R.id.appbar);
        appBarLayout.addOnOffsetChangedListener(this);
    }

Then have CheesDetailActivity implement

AppBarLayout.OnOffsetChangedListener.

我在项目中是这样处理的:

@Override
    protected void onResume() {
        super.onResume();
        mAppBarLayout.addOnOffsetChangedListener(this);
    }

    @Override
    protected void onPause() {
        super.onPause();
        mAppBarLayout.removeOnOffsetChangedListener(this);
    }

当然activity需要

implements AppBarLayout.OnOffsetChangedListener