GridView的重力不会改变

我试图改变一个GridView的重力，每当我点击一个按钮，但应用程序部署时崩溃。我不确定为什么会在XML布局中声明GridView时出现这种情况。GridView的重力不会改变

尝试上的空对象引用调用虚拟方法android.view.ViewGroup $的LayoutParams android.widget.GridView.getLayoutParams（）'

sw600dp/activity_main.xml中

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout 
    xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" 
    android:layout_height="match_parent" 
    android:layout_width="match_parent" 
    android:gravity="center" 
    android:orientation="vertical" 
    tools:context=".MainActivity"> 
    <Button 
     android:id="@+id/btn_moveup" 
     android:text="move up" 
     android:background="@android:color/transparent" 
     android:layout_height="wrap_content" 
     android:layout_width="match_parent" 
     android:layout_gravity="top" 
     android:onClick="moveup_click" 
     /> 

    <GridView 
     android:id="@+id/abslistview_main" 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:layout_gravity="center_vertical" 
     android:numColumns="auto_fit" 
     /> 

    <Button 
     android:id="@+id/btn_movedown" 
     android:text="move down" 
     android:background="@android:color/transparent" 
     android:layout_height="wrap_content" 
     android:layout_width="match_parent" 
     android:layout_gravity="bottom" 
     android:onClick="movedown_click" 
     /> 
</LinearLayout>

MainActivity.java public class MainActivity extends Activity {

Activity mActivity; 
    private Button btnUp; 
    private Button btnDown; 
    private GridView gridMain; 

    private AbsListView absListView; 
    private ArrayAdapter<MainItem> adapter; 
    private ArrayList<MainItem> mainArrayList; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 

     absListView = findViewById(R.id.abslistview_main); 
     settingData(); 

     adapter = new AbsListViewAdapter(this, R.layout.item_abslistview, mainArrayList); 
     absListView.setAdapter(adapter); 
    } 

    private void settingData() { 
     mainArrayList = new ArrayList<>(); 

     mainArrayList.add(new MainItem(R.drawable.ic_circle, getResources().getString(R.string.item_1))); 
     mainArrayList.add(new MainItem(R.drawable.ic_star, getResources().getString(R.string.item_2))); 
     mainArrayList.add(new MainItem(R.drawable.ic_square, getResources().getString(R.string.item_3))); 
     mainArrayList.add(new MainItem(R.drawable.ic_triangle, getResources().getString(R.string.item_4))); 
     mainArrayList.add(new MainItem(R.drawable.ic_rectangle, getResources().getString(R.string.item_5))); 
     mainArrayList.add(new MainItem(R.drawable.ic_crescent, getResources().getString(R.string.item_6))); 
    } 

    public void moveup_click(View view) { 
     LinearLayout.LayoutParams params = (LinearLayout.LayoutParams) gridMain.getLayoutParams(); 
     gridMain = findViewById(R.id.abslistview_main); 
     if (params.gravity == Gravity.BOTTOM) { 
      gridMain.setGravity(Gravity.CENTER_VERTICAL); 
      btnDown.setVisibility(View.VISIBLE); 
     } else if (params.gravity == Gravity.CENTER_VERTICAL) { 
      gridMain.setGravity(Gravity.TOP); 
      btnUp.setVisibility(View.GONE); 
     } 
    } 
}

来源

2017-09-29 MacaronLover

您有触发moveup_click()函数的按钮。在该函数中，首先需要GridView的LayoutParams，然后初始化gridview本身。这不是正确的顺序。

要解决该问题，您可以移动gridMain = findViewById(R.id.abslistview_main);oncreate函数或之前LinearLayout.LayoutParams params = (LinearLayout.LayoutParams) gridMain.getLayoutParams();。 -

来源

2017-09-29 18:54:02

你也取得了在创建方法

absListView = findViewById(R.id.abslistview_main);

错误与

gridMain = findViewById(R.id.abslistview_main);

删除此行

来源

2017-09-29 19:17:25

GridView的重力不会改变

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