Android：恢复recyclerview视差

Question

我尝试使用回收器视图编写自己的视差效果。目前它工作得很好......直到我不改变我的设备方向。

在状态恢复时，我取回用于计算标题 Y 转换的“指标”变量，这没有问题。 但是我在修复后由于不同的观点而无法获得身高。

基本上这是我记录的内容：

D/视差﹕gridHeight: 0 - toolbar: 0 - poster: 0

我尝试使用 .measure() 然后 getMeasuredHeight() 但这是我得到的：

D/视差：gridHeight：0 - 工具栏：128 - 海报：1108

也许我误用了 Measure。或者也许我应该在另一个时刻使用我的视差方法？ （运行时的衣服？）如果你有任何线索......

这是我阅读一年后的第一个问题。希望我做到了这一点。并感谢您的帮助；）

这是我的代码：

public class ParallaxActivity extends Activity {

    private int                     metrics = 0;
    private int                     resize = 0;
    private int                     gridHeight = -1;
    private int                     toolbarHeight = -1;
    private int                     posterHeight = -1;
    private boolean                 docked = false;

    private Toolbar                 toolbar;
    private ImageView               poster;
    private LinearLayout            header;
    private RecyclerView            grid;
    private RecyclerView.LayoutManager  manager;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_parallax2);

    toolbar = (Toolbar)findViewById(R.id.toolbar_actionbar);
    toolbar.setNavigationIcon(R.drawable.ic_launcher);
    toolbar.setNavigationOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            finish();
        }
    });

    poster = (ImageView)findViewById(R.id.poster);
    grid = (RecyclerView)findViewById(R.id.list);
    header = (LinearLayout)findViewById(R.id.header);

    manager = new GridLayoutManager(this, 2);
    grid.setLayoutManager(manager);
    DefaultItemAnimator animator = new DefaultItemAnimator();
    grid.setItemAnimator(animator);
    RecyclerGridAdapter ad = new RecyclerGridAdapter(this);
    grid.setAdapter(ad);
    ad.update();

    grid.setOnScrollListener(new RecyclerView.OnScrollListener()
    {
        @Override
        public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
            super.onScrolled(recyclerView, dx, dy);

            metrics += dy / 3;
            parallax();
        }
    });
}

@Override
protected void onSaveInstanceState(Bundle b)
{
    super.onSaveInstanceState(b);
    b.putInt("metrics", metrics);
}

@Override
protected void onRestoreInstanceState(Bundle b)
{
    super.onRestoreInstanceState(b);
    metrics = b.getInt("metrics", 0);
}

@Override
public void onAttachedToWindow()
{
    if (metrics != 0)
        parallax();
}

private void parallax()
{
    if (gridHeight == -1)
    {
        gridHeight = grid.getHeight();
        toolbarHeight = toolbar.getHeight();
        posterHeight = poster.getHeight();
        Log.d("parallax", "gridHeight: " + gridHeight + " - toolbar: " + toolbarHeight + " - poster: " + posterHeight);
    }
    if (!docked && metrics > posterHeight - toolbarHeight)
    {
        docked = true;
        toolbar.setBackgroundColor(0xff000000);
    }
    if (docked && metrics < posterHeight - toolbarHeight)
    {
        docked = false;
        toolbar.setBackgroundColor(0x00000000);
    }

    if (metrics < 0)
        resize = 0;
    else if ( metrics > posterHeight - toolbarHeight)
        resize = posterHeight - toolbarHeight;
    else
        resize = metrics;

    header.setTranslationY(-resize);
    grid.setTranslationY(-resize);
    LinearLayout.LayoutParams params = (LinearLayout.LayoutParams) grid.getLayoutParams();
    params.height = gridHeight + resize;
    grid.setLayoutParams(params);
}
}

和我的布局：

<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">

<android.support.v7.widget.Toolbar
    android:id="@+id/toolbar_actionbar"
    android:background="@null"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:elevation="5dp" />

<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">

<LinearLayout
    android:id="@+id/header"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:elevation="0dp">

        <ImageView
            android:id="@+id/poster"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:scaleType="centerCrop"
            android:adjustViewBounds="true"
            android:src="@drawable/jpeg"/>
        <TextView
            android:id="@+id/title"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="SerieKids"
            android:textSize="20dp"
            android:textColor="#ffffff"
            android:background="#000000"
            android:paddingStart="100dp"/>
</LinearLayout>

<android.support.v7.widget.RecyclerView
    android:id="@+id/list"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#000000"/>
</LinearLayout>
</RelativeLayout>

最后是我使用 measure() 的方式

if (gridHeight == -1)
{
    toolbar.measure(View.MeasureSpec.UNSPECIFIED, View.MeasureSpec.UNSPECIFIED);
    poster.measure(View.MeasureSpec.UNSPECIFIED, View.MeasureSpec.UNSPECIFIED);
    grid.measure(View.MeasureSpec.UNSPECIFIED, View.MeasureSpec.UNSPECIFIED);

    gridHeight = grid.getMeasuredHeight();
    toolbarHeight = toolbar.getMeasuredHeight();
    posterHeight = poster.getMeasuredHeight();
    Log.d("parallax", "gridHeight: " + gridHeight + " - toolbar: " + toolbarHeight + " - poster: " + posterHeight);
}

Answer 1

将onGlobalLayoutListener 添加到您的RecyclerView。这样，您就可以确保您的 parallax 例程仅在您的视图被完全绘制后才被调用。还要确保您取消注册 globalLayout 否则每次绘制视图时都会调用它（如果您使用它来控制旋转更改，那么我认为不需要删除侦听器。这样它总是会旋转时调用，因为布局将再次绘制）。

如何注册和注销布局监听器的示例：

view.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
                @Override
                public void onGlobalLayout() {
                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
                       view.getViewTreeObserver().removeOnGlobalLayoutListener(this);
                    } else {
                       view.getViewTreeObserver().removeGlobalOnLayoutListener(this);
                    }
                   //your parallax routine here
                }
            });