Java RecyclerView-交替布局
我对这个很陌生,请容忍我。下面是我的代码,用于一个简单的RecyclerView。我想在LayoutManager中交替使用StaggedGridLayout和LinearLayout 我是如何启动这两个布局的Java RecyclerView-交替布局,java,android,android-recyclerview,Java,Android,Android Recyclerview,我对这个很陌生,请容忍我。下面是我的代码,用于一个简单的RecyclerView。我想在LayoutManager中交替使用StaggedGridLayout和LinearLayout 我是如何启动这两个布局的 @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
recyclerView.setHasFixedSize(true);
staggeredGrid = new StaggeredGridLayoutManager(2, 1);
cardView = new LinearLayoutManager(this);
recyclerView.setLayoutManager(staggeredGrid);
List<ItemObjects> staggeredList = getListItemData();
RecyclerViewAdapter adapter = new RecyclerViewAdapter(MainActivity.this, staggeredList);
recyclerView.setAdapter(adapter);
}
还有错误
09-06 22:17:37.769 11853-11853/com.example.wsdw E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.wsdw, PID: 11853
java.lang.NullPointerException: Attempt to invoke virtual method 'android.support.v7.widget.RecyclerView$LayoutManager android.support.v7.widget.RecyclerView.getLayoutManager()' on a null object reference
at com.example.wsdw.MainActivity.onOptionsItemSelected(MainActivity.java:50)
at android.app.Activity.onMenuItemSelected(Activity.java:2908)
at android.support.v4.app.FragmentActivity.onMenuItemSelected(FragmentActivity.java:406)
at android.support.v7.app.AppCompatActivity.onMenuItemSelected(AppCompatActivity.java:195)
at android.support.v7.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:103)
at android.support.v7.app.AppCompatDelegateImplV9.onMenuItemSelected(AppCompatDelegateImplV9.java:667)
at android.support.v7.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:810)
at android.support.v7.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:152)
at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:957)
at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:947)
at android.support.v7.widget.ActionMenuView.invokeItem(ActionMenuView.java:616)
at android.support.v7.view.menu.ActionMenuItemView.onClick(ActionMenuItemView.java:153)
at android.view.View.performClick(View.java:5198)
at android.view.View$PerformClick.run(View.java:21147)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
据我所知,我可能做得完全错误,但如果有人能帮忙,我正在寻找一个起点。请,谢谢。RecyclerView;
RecyclerView recyclerView;
//Your Activity Name
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
recyclerView.setHasFixedSize(true);
staggeredGrid = new StaggeredGridLayoutManager(2, 1);
cardView = new LinearLayoutManager(this);
recyclerView.setLayoutManager(staggeredGrid);
List<ItemObjects> staggeredList = getListItemData();
RecyclerViewAdapter adapter = new RecyclerViewAdapter(MainActivity.this, staggeredList);
recyclerView.setAdapter(adapter);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.view_settings) {
if (recyclerView.getLayoutManager() == staggeredGrid) {
recyclerView.setAdapter(null);
recyclerView.setLayoutManager(cardView);
recyclerView.setAdapter(adapter);
adapter. notifyDataSetChanged();
return true;
}
if (recyclerView.getLayoutManager() == cardView) {
recyclerView.setAdapter(null);
recyclerView.setLayoutManager(staggeredGrid);
recyclerView.setAdapter(adapter);
adapter. notifyDataSetChanged();
return true;
}
}
return super.onOptionsItemSelected(item);
}
//您的活动名称
@凌驾
创建时受保护的void(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView=(recyclerView)findViewById(R.id.recycler\u视图);
recyclerView.setHasFixedSize(true);
StaggedGrid=新的StaggedGridLayoutManager(2,1);
cardView=新的LinearLayoutManager(此);
recyclerView.setLayoutManager(交错网格);
List staggeredList=getListItemData();
RecycleServiceAdapter=新的RecycleServiceAdapter(MainActivity.this,交错列表);
recyclerView.setAdapter(适配器);
}
@凌驾
公共布尔值onOptionsItemSelected(菜单项项){
int id=item.getItemId();
if(id==R.id.view\u设置){
if(recyclerView.getLayoutManager()==交错网格){
recyclerView.setAdapter(null);
recyclerView.setLayoutManager(cardView);
recyclerView.setAdapter(适配器);
adapter.notifyDataSetChanged();
返回true;
}
if(recyclerView.getLayoutManager()==cardView){
recyclerView.setAdapter(null);
recyclerView.setLayoutManager(交错网格);
recyclerView.setAdapter(适配器);
adapter.notifyDataSetChanged();
返回true;
}
}
返回super.onOptionsItemSelected(项目);
}
RecyclerView-RecyclerView;
//您的活动名称
@凌驾
创建时受保护的void(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView=(recyclerView)findViewById(R.id.recycler\u视图);
recyclerView.setHasFixedSize(true);
StaggedGrid=新的StaggedGridLayoutManager(2,1);
cardView=新的LinearLayoutManager(此);
recyclerView.setLayoutManager(交错网格);
List staggeredList=getListItemData();
RecycleServiceAdapter=新的RecycleServiceAdapter(MainActivity.this,交错列表);
recyclerView.setAdapter(适配器);
}
@凌驾
公共布尔值onOptionsItemSelected(菜单项项){
int id=item.getItemId();
if(id==R.id.view\u设置){
if(recyclerView.getLayoutManager()==交错网格){
recyclerView.setAdapter(null);
recyclerView.setLayoutManager(cardView);
recyclerView.setAdapter(适配器);
adapter.notifyDataSetChanged();
返回true;
}
if(recyclerView.getLayoutManager()==cardView){
recyclerView.setAdapter(null);
recyclerView.setLayoutManager(交错网格);
recyclerView.setAdapter(适配器);
adapter.notifyDataSetChanged();
返回true;
}
}
返回super.onOptionsItemSelected(项目);
}
您正在onCreate()
方法中声明一个RecyclerView RecyclerView
,因此它与您在onoptionItemSelected()
中尝试使用的RecyclerView
不同。从onCreate()
中该行开头删除RecyclerView
,“谢谢Mike,这帮了大忙。”。从那里删除了RecyclerView和适配器初始化。还按照下面发布的答案添加notifyDataSetChanged,因为我知道这非常重要。问题:将“private RecycleView RecycleView;”和“private RecycleWebAdapter;”放在main类中而不是放在onCreate类中是否是有效的编码方式?使用字段(private
变量)对这些字段稍微有效一些,因此您不必进行额外的调用,比如findViewById()
-每次在整个活动中需要它们时
。如果只需要访问单个方法中的对象,则可以在该方法中声明该对象,但显然需要在多个位置使用这些对象。您在onCreate()
方法中声明了RecyclerView RecyclerView
,因此,它与您在onOptionsItemSelected()
中尝试使用的recyclerView
不同。从onCreate()
中该行开头删除RecyclerView
,“谢谢Mike,这帮了大忙。”。从那里删除了RecyclerView和适配器初始化。还按照下面发布的答案添加notifyDataSetChanged,因为我知道这非常重要。问题:将“private RecycleView RecycleView;”和“private RecycleWebAdapter;”放在main类中而不是放在onCreate类中是否是有效的编码方式?使用字段(private
变量)对这些字段稍微有效一些,因此您不必进行额外的调用,比如findViewById()
-每次在整个活动中需要它们时
。如果您只需要访问单个方法中的对象,那么您可以在该方法中声明它,但显然需要在多个位置使用它们。
RecyclerView recyclerView;
//Your Activity Name
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
recyclerView.setHasFixedSize(true);
staggeredGrid = new StaggeredGridLayoutManager(2, 1);
cardView = new LinearLayoutManager(this);
recyclerView.setLayoutManager(staggeredGrid);
List<ItemObjects> staggeredList = getListItemData();
RecyclerViewAdapter adapter = new RecyclerViewAdapter(MainActivity.this, staggeredList);
recyclerView.setAdapter(adapter);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.view_settings) {
if (recyclerView.getLayoutManager() == staggeredGrid) {
recyclerView.setAdapter(null);
recyclerView.setLayoutManager(cardView);
recyclerView.setAdapter(adapter);
adapter. notifyDataSetChanged();
return true;
}
if (recyclerView.getLayoutManager() == cardView) {
recyclerView.setAdapter(null);
recyclerView.setLayoutManager(staggeredGrid);
recyclerView.setAdapter(adapter);
adapter. notifyDataSetChanged();
return true;
}
}
return super.onOptionsItemSelected(item);
}