设置 NumberPicker 变量的 setMinValue 时出现空指针异常

Question

我正在尝试开发一个具有 textview 和 numberpicker 的对话。当我尝试设置数字选择器的最小值时出现异常。对话代码如下：

if ( v== text_mess_limit || v == text_mess_limit_text)
        {
            final Dialog dialog = new Dialog(this);
            dialog.setContentView(R.layout.settings_number_picker_dialogue);
            dialog.setTitle("Text Messages limit");

            // set the custom dialog components - text, image and button
            TextView text = (TextView) dialog.findViewById(R.id.text);
            text.setText("Set number of messages to save");

            np = (NumberPicker) findViewById(R.id.numberPicker1);


            np.setMinValue(0);
            np.setMaxValue(10);
            np.setWrapSelectorWheel(false); 

            np.setOnValueChangedListener(this); 

            Button dialogButton = (Button) dialog.findViewById(R.id.dialogButtonCancel);
            // if button is clicked, close the custom dialog
            dialogButton.setOnClickListener(new OnClickListener() {
                @Override
                public void onClick(View v) {
                    dialog.dismiss();
                }
            });

            dialog.show();
        }

logcat的报告如下：

11-22 11:33:56.184: E/AndroidRuntime(23521): java.lang.NullPointerException
11-22 11:33:56.184: E/AndroidRuntime(23521):    at com.commlink.messaging.Settings_Activity.onClick(Settings_Activity.java:143)
11-22 11:33:56.184: E/AndroidRuntime(23521):    at android.view.View.performClick(View.java:4471)
11-22 11:33:56.184: E/AndroidRuntime(23521):    at android.view.View$PerformClick.run(View.java:18784)
11-22 11:33:56.184: E/AndroidRuntime(23521):    at android.os.Handler.handleCallback(Handler.java:808)
11-22 11:33:56.184: E/AndroidRuntime(23521):    at android.os.Handler.dispatchMessage(Handler.java:103)
11-22 11:33:56.184: E/AndroidRuntime(23521):    at android.os.Looper.loop(Looper.java:193)
11-22 11:33:56.184: E/AndroidRuntime(23521):    at android.app.ActivityThread.main(ActivityThread.java:5330)
11-22 11:33:56.184: E/AndroidRuntime(23521):    at java.lang.reflect.Method.invokeNative(Native Method)
11-22 11:33:56.184: E/AndroidRuntime(23521):    at java.lang.reflect.Method.invoke(Method.java:515)
11-22 11:33:56.184: E/AndroidRuntime(23521):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:828)
11-22 11:33:56.184: E/AndroidRuntime(23521):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:644)
11-22 11:33:56.184: E/AndroidRuntime(23521):    at dalvik.system.NativeStart.main(Native Method)

Settings_Activity.java:143行如下：

np.setMinValue(0);

为什么会出现此错误？我该如何解决这个问题？

Answer 1

a dialogue having a textview and a numberpicker

然后访问NumberPicker视图，方法与从Dialog访问TextView相同。

改变

np = (NumberPicker) findViewById(R.id.numberPicker1);

至

np = (NumberPicker) dialog. findViewById(R.id.numberPicker1);

设置 NumberPicker 变量的 setMinValue 时出现空指针异常

Null pointer exception when setting a NumberPicker variable's setMinValue

android

dialog

nullpointerexception

numberpicker