我正在创建一个应用程序，其中有4个标签显示来自网站的4个不同的供稿。我想做的是每次用户点击一个标签时在自定义标题栏中显示一个进度条，然后在加载完成后隐藏进度条。
这是我的标题栏布局：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout android:id="@+id/titlebar"
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="horizontal"
android:layout_height="30dip"
android:layout_width="fill_parent"
android:gravity="center_vertical"
android:padding="0dip"
android:background="#055843">
<TextView
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/title"
android:text="TheGangGreen"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:textColor="#ffffff"
android:layout_marginLeft="5dp"
android:layout_marginTop="4dp"
android:textStyle="bold" />
<ProgressBar
android:id="@+id/progress_bar" style="?android:attr/progressBarStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerVertical="true"
android:layout_alignParentRight="true"
android:layout_marginRight="5dp" />
</RelativeLayout>
主要课程：
public class Main extends TabActivity {
private static final String TAG = "MyActivity";
ProgressBar titleProgressBar;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_CUSTOM_TITLE);
setContentView(R.layout.main);
getWindow().setFeatureInt(Window.FEATURE_CUSTOM_TITLE, R.layout.titlebar);
titleProgressBar = (ProgressBar) findViewById(R.id.progress_bar);
titleProgressBar.setVisibility(ProgressBar.GONE);
//tab related stuff goes here
}
Handler progressHandle = new Handler(){
public void handleMessage(Message msg){
Log.d(TAG, "message = " + msg.arg1);
if(msg.arg1 == 1){ // show progress
showProgressBar();
}
else {
hideProgressBar();
}
}
};
public void showProgressBar(){
Log.d(TAG, "show progress bar");
titleProgressBar.setVisibility(ProgressBar.VISIBLE);
}
}
其中一个标签类：
public class NewsTab extends Activity {
private static final String TAG = "MyActivity";
private static final String newsURL = "http://blahblah";
ListView newsList;
FeedAdapter arrayAdapter;
ArrayList<news> news = null;
Main main;
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.newsview);
newsList = (ListView)findViewById(R.id.news_list);
news = new ArrayList<news>();
arrayAdapter = new FeedAdapter(NewsTab.this, R.layout.news_item, news);
newsList.setAdapter(arrayAdapter);
main = new Main();
new GetFeedTask().execute(this.newsURL);
}
private class GetFeedTask extends AsyncTask<String, String, String> {
@Override
protected String doInBackground(String... urls) {
// TODO Auto-generated method stub
Random randomizer = new Random(System.currentTimeMillis());
String responseBody = "";
try {
URL feedUrl = new URL(urls[0] + "?" + randomizer.nextInt(10000));
URLConnection tc = feedUrl.openConnection();
BufferedReader in = new BufferedReader(new InputStreamReader(tc.getInputStream()));
String line;
while ((line = in.readLine()) != null) {
responseBody += line;
}
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return responseBody;
}
protected void onPreExecute(){
Message msg = new Message();
msg.arg1 = 1;
main.progressHandle.sendMessage(msg);
}
protected void onPostExecute(String response) {
try {
Type collectionType = new TypeToken<ArrayList<news>>(){}.getType();
List<news> lst = new Gson().fromJson(response, collectionType);
Message msg = new Message();
msg.arg1 = 2;
main.progressHandle.sendMessage(msg);
news.clear(); // clear the adapter array so an updated list won't be appended to the existing one
for(news l : lst)
{
news.add(l);
}
arrayAdapter.notifyDataSetChanged();
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
因此，来自onPreExecute的消息正在正确发送，但是titleProgressBar.setVisibility（ProgressBar.VISIBLE）;在showProgressBar中导致NullPointerException。
谢谢
这是我的LogCat：
D/AndroidRuntime( 423): >>>>>>>>>>>>>> AndroidRuntime START <<<<<<<<<<<<<<
D/AndroidRuntime( 423): CheckJNI is ON
D/AndroidRuntime( 423): --- registering native functions ---
I/ActivityManager( 59): Starting activity: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=com.tgg.test/.SplashScreen }
D/AndroidRuntime( 423): Shutting down VM
D/dalvikvm( 423): Debugger has detached; object registry had 1 entries
I/ActivityManager( 59): Start proc com.tgg.test for activity com.tgg.test/.SplashScreen: pid=430 uid=10047 gids={3003}
I/AndroidRuntime( 423): NOTE: attach of thread 'Binder Thread #3' failed
I/ActivityManager( 59): Displayed activity com.tgg.test/.SplashScreen: 1725 ms (total 420542 ms)
I/ActivityManager( 59): Starting activity: Intent { cmp=com.tgg.test/.Main }
D/MyActivity( 430): resume
D/MyActivity( 430): message = 1
D/AndroidRuntime( 430): Shutting down VM
W/dalvikvm( 430): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
E/AndroidRuntime( 430): FATAL EXCEPTION: main
E/AndroidRuntime( 430): java.lang.NullPointerException
E/AndroidRuntime( 430): at com.tgg.test.Main.showProgressBar(Main.java:76)
E/AndroidRuntime( 430): at com.tgg.test.Main$1.handleMessage(Main.java:67)
E/AndroidRuntime( 430): at android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime( 430): at android.os.Looper.loop(Looper.java:123)
E/AndroidRuntime( 430): at android.app.ActivityThread.main(ActivityThread.java:4627)
E/AndroidRuntime( 430): at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime( 430): at java.lang.reflect.Method.invoke(Method.java:521)
E/AndroidRuntime( 430): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
E/AndroidRuntime( 430): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
E/AndroidRuntime( 430): at dalvik.system.NativeStart.main(Native Method)
W/ActivityManager( 59): Force finishing activity com.tgg.test/.Main
W/ActivityManager( 59): Activity pause timeout for HistoryRecord{450a2a20 com.tgg.test/.Main}
I/global ( 430): Default buffer size used in BufferedReader constructor. It would be better to be explicit if an 8k-char buffer is required.
I/Process ( 430): Sending signal. PID: 430 SIG: 9
I/WindowManager( 59): WIN DEATH: Window{450aa2a8 com.tgg.test/com.tgg.test.SplashScreen paused=true}
I/ActivityManager( 59): Process com.tgg.test (pid 430) has died.
答案 0 :(得分：0)
在您的父活动中，在您执行任何操作之前，您需要执行此操作 requestWindowFeature调用，然后在您的子活动中调用
getParent().setProgressBarIndeterminateVisibility(true/false);