Question

我尝试使用ListView和按钮显示简单对话框。

MainActivity.java：

package com.example.myapplication.app;

import android.app.Dialog;
import android.content.Context;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;


public class MainActivity extends ActionBarActivity {

    final Context context = this;

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


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    public void add_contact(View v) {

        final Dialog dialog = new Dialog(context);
        dialog.setContentView(R.layout.contact_list);

        final ListView lv = (ListView)findViewById(R.id.lstVw_contacts);

        String[] values = new String[] { "one","two","three" };

        final ArrayAdapter adapter = new ArrayAdapter(context,
                android.R.layout.simple_list_item_1, values);
        lv.setAdapter(adapter); // fail HERE. Without this line I take empty ListView

        Button dialogButton = (Button) dialog.findViewById(R.id.action_dialog_close);
        dialogButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                dialog.dismiss();
            }
        });
        dialog.show();
    }


     @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

}

activity_main.xml中：

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:weightSum="1"
    tools:context="com.example.myapplication.app.MainActivity">
            <Button
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="add contacts"
                android:onClick="add_contact"
                android:id="@+id/action_add_contact"/>
</FrameLayout>

contact_list.xml：

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ListView
        android:layout_width="match_parent"
        android:layout_weight="1"
        android:layout_height="0dp"
        android:id="@+id/lstVw_contacts" />

    <Button
        android:id="@+id/action_dialog_close"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Close"
        android:layout_below="@+id/text"
        android:layout_centerHorizontal="true" />

</LinearLayout>

当我使用ArrayAdapter在MainActivity中使用ListView时，它没问题。（类似代码）

当我在Dialog中使用ListView和ArrayAdapter时出现错误。

为什么呢？如何在没有ArrayAdapter的情况下从数组中填充ListView？

logcatg：

05-24 13:25:47.236    2864-2864/com.example.myapplication.app W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0xb4adcba8)
05-24 13:25:47.266    2864-2864/com.example.myapplication.app E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.example.myapplication.app, PID: 2864
    java.lang.IllegalStateException: Could not execute method of the activity
            at android.view.View$1.onClick(View.java:3823)
            at android.view.View.performClick(View.java:4438)
            at android.view.View$PerformClick.run(View.java:18422)
            at android.os.Handler.handleCallback(Handler.java:733)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5017)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.reflect.InvocationTargetException
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at android.view.View$1.onClick(View.java:3818)
            at android.view.View.performClick(View.java:4438)
            at android.view.View$PerformClick.run(View.java:18422)
            at android.os.Handler.handleCallback(Handler.java:733)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5017)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.example.myapplication.app.MainActivity.add_contact(MainActivity.java:49)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at android.view.View$1.onClick(View.java:3818)
            at android.view.View.performClick(View.java:4438)
            at android.view.View$PerformClick.run(View.java:18422)
            at android.os.Handler.handleCallback(Handler.java:733)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5017)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
            at dalvik.system.NativeStart.main(Native Method)

Answer 1

它失败了，因为ArrayAdapter没有附加到右侧Context。实际上，您应该使用this变量而不是Context作为context参数：

final ArrayAdapter adapter = new ArrayAdapter(context, android.R.layout.simple_list_item_1, values);

更新：

lv变量发生空指针异常，因为lv = null。为什么？由于ListView属于contact_list.xml而不属于activity_main.xml，因此您必须附加正确的布局才能找到ID：

final ListView lv = (ListView) dialog.findViewById(R.id.lstVw_contacts);

使用dialog.findViewById(...)是指dialog.setContentView(...)有R.layout.contact_list的内容视图，而ListView在此布局中，您需要在方法中引用它。

附件ArrayAdapter到ListView破解程序

1 个答案: