[第一次提问者和第一次安装android编码器,所以如果我做错了就道歉]
我试图在我的回收商上更改项目视图中的值。但是,如果该项目视图恰好在屏幕外,则findViewBy [layout,adapter或id]将显示为null。
public void setUserActive(UserListAdapter adapter, RecyclerView recyclerView, int position, View v) {recyclerView.findViewHolderForItemId(adapter.getItemId(position));
TextView txtActive = (TextView) vh.itemView.findViewById(R.id.user_isActive);
txtActive.setText("Active");
UserListAdapter.ViewHolder inactivevh = (UserListAdapter.ViewHolder) recyclerView.findViewHolderForItemId(adapter.getItemId(adapter.getActiveUserPosition()));
TextView txtInActive = (TextView) inactivevh.itemView.findViewById(R.id.user_isActive);
txtInActive.setText("");
adapter.setActiveUserPosition(position);
}
我尝试了几种不同的方式,使用
UserListAdapter.ViewHolder vh = (UserListAdapter.ViewHolder) recyclerView.findViewHolderForLayoutPosition(position);
或
UserListAdapter.ViewHolder inactivevh = (UserListAdapter.ViewHolder) recyclerView.findViewHolderForAdapterPosition(position)
当应该处于inactivevh的视图不在屏幕上时,它们都会失败。
我已将适配器设置为hasStableIDs = true notifydatasetchanged似乎也无济于事。
答案 0 :(得分:8)
如果某个项目在屏幕上(布局),您可以使用您描述的方法方便地获取其视图保持器。 如果某个项目不在屏幕上,它会在通过onBindViewHolder
滚动后立即更新。如果它没有滚动进入,则不会向用户显示任何尝试更新它是浪费处理能力(除了不可能,因为该项目没有分配视图持有者)。
含义:以onBindViewHolder
能够提取最新数据的方式实现适配器。看起来你已经完成所有设置并且可以使用它:
public void setUserActive(UserListAdapter adapter, RecyclerView recyclerView, int position) {
// Retrieve the old active user ID so we can mark him deactivated.
final int oldUserActivePosition = adapter.getActiveUserPosition();
// Setup the adapter with current data.
adapter.setActiveUserPosition(position);
// Do NOT use stable IDs and this method. It just doesn't work as expected.
// recyclerView.findViewHolderForItemId(adapter.getItemId(position));
// Activate new user.
UserListAdapter.ViewHolder holder = (UserListAdapter.ViewHolder) recyclerView.findViewHolderForAdapterPosition(position);
if (holder == null) {
// The item is off screen, no need to update it yet.
} else {
// Update the on screen item. The logic is already implemented in the adapter.
adapter.onBindViewHolder(holder, position);
}
// Deactivate previous user.
holder = (UserListAdapter.ViewHolder) recyclerView.findViewHolderForAdapterPosition(oldUserActivePosition);
if (holder != null) {
adapter.onBindViewHolder(holder, oldUserActivePosition);
}
}
当然,简化代码中的if-else块。
我刚刚意识到原始解决方案是多么复杂。只要适配器可以对onBindViewHolder
中所需的所有事件作出反应,并且绑定非常简单,这就足够了:
public void setActiveUserPosition(int position) {
if (mActiveUserPosition != position) {
int oldPosition = mActiveUserPosition;
mActiveUserPosition = position;
notifyItemChanged(oldPosition);
notifyItemChanged(position);
}
}
现在需要调用的只是adapter.setActiveUserPosition(position);
,这会使setUserActive
方法过时。