Android群英传——第四章自动显示隐藏ActionBar/Toolbar的ListView

这中效果最为常见：
当ListView向上滑动的时候，Toolbar进行隐藏，当向下滑动时，Toolbar则又显示出来了。
如图

完整代码实现如下：

import android.animation.ObjectAnimator;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewConfiguration;
import android.widget.AbsListView;
import android.widget.ArrayAdapter;
import android.widget.ListView;

public class MainActivity extends AppCompatActivity {

    private Toolbar mToolbar;
    private ListView mListView;
    private String[] mStr = new String[20];
    private int mTouchSlop;
    private float mFirstY;
    private float mCurrentY;
    private int direction;
    private ObjectAnimator mAnimator;
    private boolean mShow = true;

    View.OnTouchListener myTouchListener = new View.OnTouchListener() {
        @Override
        public boolean onTouch(View v, MotionEvent event) {
            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    mFirstY = event.getY();
                    break;
                case MotionEvent.ACTION_MOVE:
                    mCurrentY = event.getY();
                    // 判断滑动方向
                    if (mCurrentY - mFirstY > mTouchSlop) {
                        direction = 0;// down
                    } else if (mFirstY - mCurrentY > mTouchSlop) {
                        direction = 1;// up
                    }

                    // 根据滑动方向播放toolbar的隐藏或者显示的动画
                    if (direction == 1) {
                        if (mShow) {
                            toolbarAnim(1);//show
                            mShow = !mShow;
                        }
                    } else if (direction == 0) {
                        if (!mShow) {
                            toolbarAnim(0);//hide
                            mShow = !mShow;
                        }
                    }
                    break;
                case MotionEvent.ACTION_UP:
                    break;
            }
            return false;
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mTouchSlop = ViewConfiguration.get(this).getScaledTouchSlop();
        mToolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(mToolbar);
        mListView = (ListView) findViewById(R.id.listView);
        for (int i = 0; i < mStr.length; i++) {
            mStr[i] = "Item " + i;
        }
        // 也可以使用
        // (int) getResources().getDimension(R.dimen.abc_action_bar_default_height_material)方法
        // 获取系统Toolbar的默认高度，但是不建议这么做，如果你要对Toolbar的高度进行定制，这个值并不能达到预期的效果
        int w = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
        int h = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
        mToolbar.measure(w, h);
        int toolbarHeight = mToolbar.getMeasuredHeight();
        View header = new View(this);
        header.setLayoutParams(new AbsListView.LayoutParams(
                AbsListView.LayoutParams.MATCH_PARENT,
                toolbarHeight));
        Log.i("logi", "====" + getSupportActionBar().getHeight());
        mListView.addHeaderView(header);
        mListView.setAdapter(new ArrayAdapter<String>(
                MainActivity.this,
                android.R.layout.simple_expandable_list_item_1,
                mStr));
        mListView.setOnTouchListener(myTouchListener);
    }

    private void toolbarAnim(int flag) {
        if (mAnimator != null && mAnimator.isRunning()) {
            mAnimator.cancel();
        }
        if (flag == 0) {
            mAnimator = ObjectAnimator.ofFloat(mToolbar,
                    "translationY", mToolbar.getTranslationY(), 0);
        } else {
            Log.i("logi", "===height" + mToolbar.getHeight());
            Log.i("logi", "===ty" + mToolbar.getTranslationY());
            // 使用属性动画将y偏移
            mAnimator = ObjectAnimator.ofFloat(mToolbar,
                    "translationY", mToolbar.getTranslationY(),
                    -mToolbar.getHeight());
        }
        mAnimator.start();
    }
}