Android平滑的加载项目
示例
如果您RecyclerView从网络中加载数据中的项目（通常是图像）或执行其他处理，这可能会花费大量时间，并且最终可能会在屏幕上显示项目，但未完全加载。为避免这种情况，您可以扩展现有LinearLayoutManager项以在屏幕上可见之前预加载许多项：
package com.example;
import android.content.Context;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.OrientationHelper;
import android.support.v7.widget.RecyclerView;
/**
* A LinearLayoutManager that preloads items off-screen.
* <p>
* Preloading is useful in situations where items might take some time to load
* fully, commonly because they have maps, images or other items that require
* network requests to complete before they can be displayed.
* <p>
* By default, this layout will load a single additional page's worth of items,
* a page being a pixel measure equivalent to the on-screen size of the
* recycler view. This can be altered using the relevant constructor, or
* through the {@link #setPages(int)} method.
*/
public class PreLoadingLinearLayoutManager extends LinearLayoutManager {
private int mPages = 1;
private OrientationHelper mOrientationHelper;
public PreLoadingLinearLayoutManager(final Context context) {
super(context);
}
public PreLoadingLinearLayoutManager(final Context context, final int pages) {
super(context);
this.mPages= pages;
}
public PreLoadingLinearLayoutManager(final Context context, final int orientation, final boolean reverseLayout) {
super(context, orientation, reverseLayout);
}
@Override
public void setOrientation(final int orientation) {
super.setOrientation(orientation);
mOrientationHelper = null;
}
/**
* Set the number of pages of layout that will be preloaded off-screen,
* a page being a pixel measure equivalent to the on-screen size of the
* recycler view.
* @param pages the number of pages; can be {@code 0} to disable preloading
*/
public void setPages(final int pages) {
this.mPages= pages;
}
@Override
protected int getExtraLayoutSpace(finalRecyclerView.Statestate) {
if (mOrientationHelper == null) {
mOrientationHelper = OrientationHelper.createOrientationHelper(this, getOrientation());
}
return mOrientationHelper.getTotalSpace() * mPages;
}
}