设置ListView项目的背景？

Question

So, I have this ListView , which I would like that each one of its items had a background (the same background for all of them). So far I've been trying to use this code:

listView = (ListView) findViewById(R.id.listView);
ArrayAdapter<CharSequence> lv = ArrayAdapter.createFromResource(this,
            R.array.countries_array, android.R.layout.simple_list_item_1);
listView.setAdapter(lv);

---

for (Integer i = 0; i < listView.getCount(); ++i) {
    View listItem = listView.getChildAt(i);
    listItem.setBackgroundResource(R.drawable.edittext_custom);
}

It's simple, I increment i and then use it to know the position in which it is and it will set that items background, and it repeats until all items have the same background. Sound easy. Is there a better way to do this? If not, can someone please help figure it out why this simple code doesn't work? I'm pretty sure I'm missing something basic.

Exception:

05-18 15:08:45.659  10157-10157/com.example.fabiocompany.goquiz W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x41917da0)
05-18 15:08:45.679  10157-10157/com.example.fabiocompany.goquiz E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.example.fabiocompany.goquiz, PID: 10157
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.fabiocompany.goquiz/com.example.fabiocompany.goquiz.TopicosActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2328)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2386)
            at android.app.ActivityThread.access$900(ActivityThread.java:169)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1277)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5476)
            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:1283)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.example.fabiocompany.goquiz.TopicosActivity.onCreate(TopicosActivity.java:47)
            at android.app.Activity.performCreate(Activity.java:5451)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1093)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2292)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2386)
            at android.app.ActivityThread.access$900(ActivityThread.java:169)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1277)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5476)
            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:1283)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099)
            at dalvik.system.NativeStart.main(Native Method)

XML:

<RelativeLayout 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:background="@drawable/bggoquiz"
    tools:context="com.example.fabiocompany.goquiz.TopicosActivity"
    android:focusable="true"
    android:focusableInTouchMode="true">

    <ListView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/listView"
        android:layout_below="@+id/searchView"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true"
        android:layout_marginTop="10dp"
        android:divider="@android:color/transparent"
        android:dividerHeight="20.0sp"
        />

    <SearchView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/searchView"
        android:background="@drawable/edittext_custom"
        android:layout_alignParentTop="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true" />

</RelativeLayout>

If you need something else, please do tell, I'll try to help.

Answer 1

Instead of doing all this you could create a new xml file named listitem.xml with textview as below

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/tv_item"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background = "<give your desired background>"
/>

Modify your ArrayAdapter to

ArrayAdapter<String> lv = new ArrayAdapter<String>(this,
            R.layout.listitem, R.id.tv_item, <your array>);

As you are applying same background to all items simply setting it ones in xml will do the work. You do not require to loop through list.

Answer 2

Problem is with your this method,. listView.getChildAt(i); this works only on the items which are currently visible So this is how you need to use them.

final int numVisibleChildren = listView.getChildCount();
final int firstVisiblePosition = listView.getFirstVisiblePosition();
for (int i = firstVisiblePosition; i < firstVisiblePosition + numVisibleChildren; i++) {
     View view = listView.getChildAt(i - firstVisiblePosition);
     listItem.setBackgroundResource(R.drawable.edittext_custom);
}

Answer 3

Assuming that listView.getChildAt is returning null because the corresponding position has an invisible (or non-existent) object, then simply test for null ...

for (Integer i = 0; i < listView.getCount(); ++i) {
    View listItem = listView.getChildAt(i);
    if (listItem != null) {
        listItem.setBackgroundResource(R.drawable.edittext_custom);
    }
}