我有点新的AsyncTask和ProgressDialog,我得到一个空指针异常错误,每当我调用我的按钮上的new MyTask().execute();
我的方法是不对的?我的代码有什么问题,或者我错过了什么?
进程只应该它应该进程取决于当前选择的TabHost
,所以…
public class MyTask extends AsyncTask<Void, Integer, Void>{
@Override
protected void onPreExecute() {
//Show progress Dialog here
super.onPreExecute();
progress.show();
}
@Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
//Update UI here if needed
//Dismiss Progress Dialog here
progress.dismiss();
}
@Override
protected Void doInBackground(Void... params) {
SparseBooleanArray laptopBooleanArray = laptopLV.getCheckedItemPositions();
SparseBooleanArray mp3BooleanArray = mp3LV.getCheckedItemPositions();
SparseBooleanArray mobilepBooleanArray = mobileLV.getCheckedItemPositions();
switch (th.getCurrentTab()) {
case 0:
for(int i = 0; i < laptopLV.getCount(); i++)
{
if(laptopBooleanArray.get(i) == true)
{
selectedFromLaptopList.add(laptopLV.getItemAtPosition(i).toString());
}
}
handler.setItemListData(TechiesActivity.this, "Techies", selectedFromLaptopList, "Unit" , "Laptop" , "Store");
displayView();
drawer.closeMenu();
selectedFromLaptopList.clear();
break;
case 1:
for(int i = 0; i < mp3LV.getCount(); i++)
{
if(mp3BooleanArray.get(i) == true)
{
selectedFromLaptopList.add(mp3LV.getItemAtPosition(i).toString());
}
}
handler.setItemListData(TechiesActivity.this, "Techies", selectedFromMp3List, "Unit" , "Mp3" , "Store");
displayView();
drawer.closeMenu();
selectedFromLaptopList.clear();
break;
case 2:
for(int i = 0; i < mobileLV.getCount(); i++)
{
if(mobilepBooleanArray.get(i) == true)
{
selectedFromLaptopList.add(mobileLV.getItemAtPosition(i).toString());
}
}
handler.setItemListData(TechiesActivity.this, "Techies", selectedFromMobileList, "Unit" , "Mobile" , "Store");
displayView();
drawer.closeMenu();
selectedFromLaptopList.clear();
break;
}
return null;
}
}
,下面是LogCat错误:
03-05 13:15:05.650: E/AndroidRuntime(497): FATAL EXCEPTION: AsyncTask #1
03-05 13:15:05.650: E/AndroidRuntime(497): java.lang.RuntimeException: An error occured while executing doInBackground()
03-05 13:15:05.650: E/AndroidRuntime(497): at android.os.AsyncTask$3.done(AsyncTask.java:200)
03-05 13:15:05.650: E/AndroidRuntime(497): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
03-05 13:15:05.650: E/AndroidRuntime(497): at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
03-05 13:15:05.650: E/AndroidRuntime(497): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
03-05 13:15:05.650: E/AndroidRuntime(497): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
03-05 13:15:05.650: E/AndroidRuntime(497): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1068)
03-05 13:15:05.650: E/AndroidRuntime(497): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:561)
03-05 13:15:05.650: E/AndroidRuntime(497): at java.lang.Thread.run(Thread.java:1096)
03-05 13:15:05.650: E/AndroidRuntime(497): Caused by: android.view.ViewRoot$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
03-05 13:15:05.650: E/AndroidRuntime(497): at android.view.ViewRoot.checkThread(ViewRoot.java:2802)
03-05 13:15:05.650: E/AndroidRuntime(497): at android.view.ViewRoot.invalidateChild(ViewRoot.java:607)
03-05 13:15:05.650: E/AndroidRuntime(497): at android.view.ViewRoot.invalidateChildInParent(ViewRoot.java:633)
03-05 13:15:05.650: E/AndroidRuntime(497): at android.view.ViewGroup.invalidateChild(ViewGroup.java:2505)
03-05 13:15:05.650: E/AndroidRuntime(497): at android.view.View.invalidate(View.java:5139)
03-05 13:15:05.650: E/AndroidRuntime(497): at android.widget.AbsListView.resetList(AbsListView.java:1011)
03-05 13:15:05.650: E/AndroidRuntime(497): at android.widget.ListView.resetList(ListView.java:493)
03-05 13:15:05.650: E/AndroidRuntime(497): at android.widget.ListView.setAdapter(ListView.java:422)
03-05 13:15:05.650: E/AndroidRuntime(497): at com.shop.browser.TechiesActivity.displayView(TechiesActivity.java:98)
03-05 13:15:05.650: E/AndroidRuntime(497): at com.shop.browser.TechiesActivity$MyTask.doInBackground(TechiesActivity.java:257)
03-05 13:15:05.650: E/AndroidRuntime(497): at com.shop.browser.TechiesActivity$MyTask.doInBackground(TechiesActivity.java:1)
03-05 13:15:05.650: E/AndroidRuntime(497): at android.os.AsyncTask$2.call(AsyncTask.java:185)
03-05 13:15:05.650: E/AndroidRuntime(497): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
03-05 13:15:05.650: E/AndroidRuntime(497): ... 4 more
03-05 13:15:07.850: E/WindowManager(497): Activity com.shop.browser.TechiesActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@44f93528 that was originally added here
03-05 13:15:07.850: E/WindowManager(497): android.view.WindowLeaked: Activity com.shop.browser.TechiesActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@44f93528 that was originally added here
03-05 13:15:07.850: E/WindowManager(497): at android.view.ViewRoot.<init>(ViewRoot.java:247)
03-05 13:15:07.850: E/WindowManager(497): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:148)
03-05 13:15:07.850: E/WindowManager(497): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:91)
03-05 13:15:07.850: E/WindowManager(497): at android.view.Window$LocalWindowManager.addView(Window.java:424)
03-05 13:15:07.850: E/WindowManager(497): at android.app.Dialog.show(Dialog.java:241)
03-05 13:15:07.850: E/WindowManager(497): at com.shop.browser.TechiesActivity$MyTask.onPreExecute(TechiesActivity.java:233)
03-05 13:15:07.850: E/WindowManager(497): at android.os.AsyncTask.execute(AsyncTask.java:391)
03-05 13:15:07.850: E/WindowManager(497): at com.shop.browser.TechiesActivity.onClick(TechiesActivity.java:181)
03-05 13:15:07.850: E/WindowManager(497): at java.lang.reflect.Method.invokeNative(Native Method)
03-05 13:15:07.850: E/WindowManager(497): at java.lang.reflect.Method.invoke(Method.java:521)
03-05 13:15:07.850: E/WindowManager(497): at android.view.View$1.onClick(View.java:2067)
03-05 13:15:07.850: E/WindowManager(497): at android.view.View.performClick(View.java:2408)
03-05 13:15:07.850: E/WindowManager(497): at android.view.View$PerformClick.run(View.java:8816)
03-05 13:15:07.850: E/WindowManager(497): at android.os.Handler.handleCallback(Handler.java:587)
03-05 13:15:07.850: E/WindowManager(497): at android.os.Handler.dispatchMessage(Handler.java:92)
03-05 13:15:07.850: E/WindowManager(497): at android.os.Looper.loop(Looper.java:123)
03-05 13:15:07.850: E/WindowManager(497): at android.app.ActivityThread.main(ActivityThread.java:4627)
03-05 13:15:07.850: E/WindowManager(497): at java.lang.reflect.Method.invokeNative(Native Method)
03-05 13:15:07.850: E/WindowManager(497): at java.lang.reflect.Method.invoke(Method.java:521)
03-05 13:15:07.850: E/WindowManager(497): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
03-05 13:15:07.850: E/WindowManager(497): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
03-05 13:15:07.850: E/WindowManager(497): at dalvik.system.NativeStart.main(Native Method)
请求按钮的代码:
public void onClick (View v) {
new MyTask().execute();
}
使用MyTask类构造函数传递活动上下文来初始化ProgressDialog和消息,您希望在onPreExecute
中的ProgressDialog中显示为:
public class MyTask extends AsyncTask<Void, Integer, Void>{
Context context;
String str_mesg;
ProgressDialog progress;
public MyTask(Context context, String str_mesg){
this.context=context;
this.str_mesg=str_mesg;
}
@Override
protected void onPreExecute() {
//Show progress Dialog here
super.onPreExecute();
// create ProgressDialog here ...
progress = new ProgressDialog(context);
progress.setMessage(str_mesg);
// set other progressbar attributes
....
progress.show();
}
// your code here....
和启动AsyncTask作为按钮点击:
button.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
// TODO Auto-generated method stub
new MyTask(Your_Current_Activity.this).execute();
}
});
听起来进度对话框没有被初始化,所以请确保它被正确初始化。
protected void onPreExecute() {
super.onPreExecute();
//initialize progress dialog here
progress.show();
}
EDIT:
class YourClass extends AsyncTask<...>
{
ProgressDialog progress;
Protected void onPreExecute(){
// create dialog here
progress = new ProgressDialog (...);
progress.setMessage(...);
progress.show();
}
protected void onPostExecute(...){
// dismiss dialog here
progress.dismiss();
}
}
另一部分,我希望它有帮助…如果你想在后台任务期间更改文本和进度百分比,你可以定义一个处理程序
public class MyTask extends AsyncTask<Void, Integer, Void>
{
private ProgressDialog progressDialog;
private String mstepDescription;
protected int mprogressPercentage;
private String mstepDescription;
protected int mprogressPercentage;
Handler handle = new Handler() {
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
progressDialog.setMessage(mstepDescription);
progressDialog.setProgress(mprogressPercentage);
}
};
void Step (String StepDescription, int Progress)
{
mstepDescription = StepDescription;
mprogressPercentage = Progress;
handle.sendMessage(handle.obtainMessage());
}
Protected void onPreExecute()
{
// create dialog here
progress = new ProgressDialog (...);
progress.setMessage(...);
progress.show();
}
protected void onPostExecute(...){
// dismiss dialog here
progress.dismiss();
}
@Override
protected Void doInBackground(Void... params)
{
// do somthing
Step("...", 40);
// do something else
}
}