java - 我的警报对话框自定义布局出现问题

Question

制定待办事项列表。有两个问题，不太重要的问题是，由于某种原因，我看不到我设置为“标签”的 TextView。更重要的是，当我单击“创建新任务”按钮时，会弹出警报，我可以将值放入 EditText 框中，但是当我点击“创建”时，它会崩溃，并且出现 NullPointer 异常，提示我正在尝试调用getText() 对空对象引用。我无法弄清楚我是否错误地膨胀，或者我是否没有正确地将 EditTexts 链接到警报。烦人的是，我的编辑文本警报框可以很好地编辑现有列表项(我硬编码用于测试)。这是我的布局和 Activity ，我评论了它中断的行。对所有 Log.d 感到抱歉，我真的很想想象这一切是如何工作的。

布局

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent" android:layout_height="match_parent">

    <EditText
        android:layout_width="55dp"
        android:layout_height="wrap_content"
        android:inputType="number"
        android:ems="10"
        android:id="@+id/txtCreatePriority"
        android:layout_centerVertical="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_marginLeft="25dp"
        android:hint="1"
        android:textAlignment="center" />

    <EditText
        android:layout_width="235dp"
        android:layout_height="wrap_content"
        android:id="@+id/txtCreateItemContent"
        android:layout_centerVertical="true"
        android:layout_toRightOf="@+id/txtCreatePriority"
        android:layout_toEndOf="@+id/txtCreatePriority"
        android:layout_marginLeft="15dp"
        android:hint="Do Laundry"
        android:textAlignment="center" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="Priority"
        android:id="@+id/lblPriority"
        android:layout_above="@+id/txtCreatePriority"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_marginLeft="17dp"
        android:textStyle="bold"
        android:textSize="23dp" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:text="Task to-do"
        android:id="@+id/lblItemContent"
        android:layout_above="@+id/txtCreateItemContent"
        android:layout_toRightOf="@+id/lblPriority"
        android:layout_toEndOf="@+id/lblPriority"
        android:layout_marginLeft="65dp"
        android:textStyle="bold"
        android:textSize="23dp" />
</RelativeLayout>

Activity

public class MainActivity extends AppCompatActivity {

    private ListDataSource ds;
    private ListView listViewToDo;
    private Button btnAddNew;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final Context context = this;
        Log.d("MainActivity","Attempting to create data source");
        try {
            ds = new ListDataSource();
        }
        catch(Exception e)
        {
            e.printStackTrace();
            Log.d("MainActivity","Failed to create data source");
        }
        btnAddNew = (Button)findViewById(R.id.btnAddNew);
        Log.d("Main Activity","Attempting to link empty list view to on screen view");
        listViewToDo = (ListView)findViewById(R.id.listOfLists);
        Log.d("Main Activity", "Views linked, Attempting to set adapter to listView");
        listViewToDo.setAdapter(new ListDataSourceAdapter(this, ds));
        Log.d("Main Activity", "Successfully set Adapter");
        btnAddNew.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.d("addItem", "Entered onclick, Attempting to create AlertDialog");
                AlertDialog.Builder addItem = new AlertDialog.Builder(context);
                Log.d("addItem", "AlertDialog Built, attempting to create inflater");
                LayoutInflater inflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
                addItem.setView(inflater.inflate(R.layout.create_item_layout, null));
                Log.d("addItem", "inflater built linking text boxes");
                final TextView txtCreatePriority = (TextView)findViewById(R.id.txtCreatePriority);
                final TextView txtCreateCellContent = (TextView)findViewById(R.id.txtCreateItemContent);
                final TextView lblPriority = (TextView)findViewById(R.id.lblPriority);
                final TextView lblItemContent = (TextView)findViewById(R.id.lblItemContent);
                addItem.setTitle("Create new item");
                addItem
                        .setCancelable(false)
                        .setPositiveButton("Create", new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int id) {
                                Log.d("editText onClick", "in onClick method, preparing to add entry");
                                // This is where the code breaks
                                ds.getList().add(Integer.valueOf(txtCreatePriority.getText().toString()), new CellContent(Integer.valueOf(txtCreatePriority.getText().toString()) + 1, txtCreateCellContent.getText().toString().trim()));
                                Log.d("editText onClick", "added new entry");
                                ListDataSourceAdapter adapter = new ListDataSourceAdapter(context, ds);
                                Log.d("editText onClick", "reestablished link to adapter");
                                listViewToDo.setAdapter(adapter);
                                Log.d("editText onClick", "adapter set");
                                adapter.notifyDataSetChanged();
                                Log.d("editText onClick", "DataSetChanged");
                            }
                        })
                        .setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int id) {
                                dialog.cancel();
                            }
                        });
                AlertDialog alertDialog = addItem.create();
                alertDialog.show();
            }
        });
        // add button listener
        listViewToDo.setOnItemClickListener(new AdapterView.OnItemClickListener()
        {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, final int position, long id)
            {
                AlertDialog.Builder editItem = new AlertDialog.Builder(context);
                final EditText edittext = new EditText(context);
                editItem.setTitle("Change item");
                editItem
                        .setMessage("Set new todo item")
                        .setView(edittext)
                        .setCancelable(false)
                        .setPositiveButton("Submit", new DialogInterface.OnClickListener()
                        {
                            public void onClick(DialogInterface dialog, int id)
                            {
                                Log.d("editText onClick","in onClick method, preparing to remove previous entry");
                                ds.getList().remove(position);
                                Log.d("editText onClick", "removed previous entry");
                                ds.getList().add(position, new CellContent(position + 1, edittext.getText().toString().trim()));
                                Log.d("editText onClick", "added new entry");
                                ListDataSourceAdapter adapter = new ListDataSourceAdapter(context,ds);
                                Log.d("editText onClick","reestablished link to adapter");
                                listViewToDo.setAdapter(adapter);
                                Log.d("editText onClick", "adapter set");
                                adapter.notifyDataSetChanged();
                                Log.d("editText onClick", "DataSetChanged");
                            }
                        })
                        .setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int id) {
                                dialog.cancel();
                            }
                        });
                AlertDialog alertDialog = editItem.create();
                alertDialog.show();
            }
        });
    }
}

错误

java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference

Answer 1

您正在 View v 上调用“(EditText)v.findViewById”。 View v 是 onClickListener 中传回的 View ，即按钮本身。由于该按钮中不包含 EditText，因此这些 View 为空。当您尝试访问它们时会崩溃。

我有点不确定带有编辑文本的布局在这段代码中的位置。是和listview在同一个布局中，还是在create_item_layout中？

如果是 create_item_layout，则需要在获取 EditText 之前对其进行扩充。使用您膨胀的 View 来 findViewById。