我有片段,我称之为自定义视图类(Dragger)
public class CanvasFragment extends Fragment {
private Dragger dragger;
public CanvasFragment() {
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setRetainInstance(true);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_canvas, container, false);
dragger = (Dragger) rootView.findViewById(R.id.dragger);
int[] symbolIndex = {};
dragger.setElementsArray(symbolIndex);
return rootView;
}
public void addIconToCanvas(int id){
dragger.addIcon(id);
}
}
我还有另一个带有RecyclerView
和适配器的片段,其中我通过主机 Activity 调用CanvasFragment's
方法addIconToCanvas()
CanvasFragment
.
public class ItemAdapter extends RecyclerView.Adapter<ItemAdapter.ViewHolder> {
private int[] data;
private Context context;
public static class ViewHolder extends RecyclerView.ViewHolder {
public ImageView itemView;
public ViewHolder(View v) {
super(v);
itemView = (ImageView) v.findViewById(R.id.im_item);
}
}
public ItemAdapter(Context context, int[] myDataset) {
data = myDataset;
this.context = context;
}
@Override
public ItemAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_view, parent, false);
ViewHolder vh = new ViewHolder(v);
return vh;
}
@Override
public void onBindViewHolder(ViewHolder holder, final int position) {
holder.itemView.setImageResource(data[position]);
holder.itemView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
((MainActivity)context).addItemToCanvas(data[position]);
}
});
}
@Override
public int getItemCount() {
return data.length;
}
}
我发现在旋转后dragger
CanvasFragment
会获得新的引用,但是当我从适配器调用addIconToCanvas()
时 - dragger
为空。
我真的不明白为什么字段得到引用然后丢失它
)))有谁知道,这有什么问题?
提前感谢!
附言:主机活动
public class MainActivity extends AppCompatActivity {
private CanvasFragment canvasFragment = new CanvasFragment();
private ItemsFragment itemsFragment = new ItemsFragment();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container_canvas, canvasFragment)
.commit();
getSupportFragmentManager().beginTransaction()
.add(R.id.container_items, itemsFragment)
.commit();
}
}
public void addItemToCanvas(int id){
canvasFragment.addIconToCanvas(id);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
用线
private CanvasFragment canvasFragment = new CanvasFragment();
每次创建Activity
时,您都会将Fragment
的新实例分配给变量 canvasFragment。但前提是savedInstanceState == null
将 CanvasFragment 的这个实例添加到 UI 中。
仅当需要显示Fragment
时,才会调用 Fragment
方法 onCreateView()
,因此在配置更改后,拖动器对于新创建的实例保持 null。
你能做什么?
仅当您要将其添加到 UI 时,才创建 CanvasFragment 的实例。在savedInstanceState != null
的情况下,找到已经存在的Fragment
,如下所示:
canvasFragment = (CanvasFragment)getSupportFragmentManager().findFragmentById(R.id.container_canvas);
从你的片段中删除 setRetainInstance(true) 行并尝试。
这样说:
androidConfigChanges: "keyboardHidden | orientation | screenSize"
在你的安卓XML文件中,你的主活动是定义的。
<activity
android:name="com.projectname.MainActivity"
android:label = "@string/title_activity_main"
</activity>
那么它应该是这样的运气:
<activity
android:name="com.projectname.MainActivity"
androidConfigChanges: "keyboardHidden | orientation | screenSize"
android:label = "@string/title_activity_main"
</activity>