Question

我有一个列表视图，当我点击一个项目时，它应该显示一个带有Radiobuttons的AlertDialog。但是当调用alertDialog时，应用程序崩溃了。 Logcat给出了NullPointerException。我做错了什么？

private void registerClickCallBack() {
        ListView list = (ListView) findViewById(R.id.settingsList);
        list.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View viewClicked,
                    int position, long id) {

                if (position == 0) {
                    final AlertDialog levelDialog

                    final CharSequence[] items = { " Easy ", " Medium ",
                            " Hard ", " Very Hard " };

                    AlertDialog.Builder builder = new AlertDialog.Builder(
                            MyActivity.this);
                    builder.setTitle("Select The Difficulty Level");

                    builder.setSingleChoiceItems(items, -1,
                            new DialogInterface.OnClickListener() {
                                public void onClick(DialogInterface dialog,
                                        int item) {
                                    Intent i = new Intent(
                                            getApplictionContext(),
                                            MyActivity.class);

                                    switch (item) {
                                    case 0:
                                        String msg = "Alert A";
                                        Toast.makeText(
                                                MyActivity.this,
                                                msg, Toast.LENGTH_LONG).show();
                                        break;
                                    case 1:
                                        String msga = "Alert B";
                                        Toast.makeText(
                                                MyActivity.this,
                                                msga, Toast.LENGTH_LONG).show();

                                        break;
                                    case 2:
                                        String msgz = "Alert C";
                                        Toast.makeText(
                                                MyActivity.this,
                                                msgz, Toast.LENGTH_LONG).show();
                                        break;
                                    case 3:
                                        String msge = "Alert E";
                                        Toast.makeText(
                                                MyActivity.this,
                                                msge, Toast.LENGTH_LONG).show();
                                        break;

                                    }

                                }
                            });
                     levelDialog.dismiss();
 levelDialog = builder.create();
 levelDialog.show();
                }

                else if (position == 1) {
                    String msg = "1";
                    Toast.makeText(MyActivity.this, msg,
                            Toast.LENGTH_LONG).show();
                } else if (position == 2) {
                    String msg = "2";
                    Toast.makeText(MyActivity.this, msg,
                            Toast.LENGTH_LONG).show();
                }

                else if (position == 3) {
                    String msg = "3";
                    Toast.makeText(MyActivity.this, msg,
                            Toast.LENGTH_LONG).show();
                }
            }
        });
    }

Answer 1

在实例化之前，您正在调用levelDialog上的函数

     levelDialog.dismiss();
     levelDialog = builder.create();
     levelDialog.show();

将其更改为

     levelDialog = builder.create();
     levelDialog.show();
     levelDialog.dismiss();

但我不确定你为什么要在那里打dismiss()。如果这没有解决它，那么请发布logcat，以便我们知道NPE的位置。为了更清楚，切换这些行应该会修复NPE，但不应该在那里调用dismiss()。

修改

取出这个

AlertDialog levelDialog=null;

并在此处声明并初始化

final AlertDialog levelDialog = builder.create(); levelDialog.show();

并在dismiss()中致电onClick()，但使用dialog.dismiss()代替levelDialog.dismiss()

此外，通常最好使用Activity Context代替Application Context，因此在您的Intent中，您可以将getApplicationContext()更改为MyActivity.this

Android - 单击listitem以显示AlertDialog时出现Nullpointer异常

1 个答案: