我正在尝试设计一个直接从URL读取笑话的应用程序，但出于某种原因，当我按下按钮启动该过程时，我无法弄清楚它是否会崩溃。
我使用两个按钮，一个读一个笑话，另一个读三个笑话。 单击第一个按钮时，它将调用AsyncTask，从URL中提取读数并显示进度条，直到笑话下载。 第二个按钮执行相同但下载3个笑话而不是一个。 这是mainActivity类。
public class MainActivity extends AppCompatActivity {
private Button oneJokeBtn, threeJokesBtn;
private TextView mJokeTv;
private final static String ERROR_TAG = "Download Error";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Capturing the TextView from our View
mJokeTv = findViewById(R.id.tv_joke);
// Capturing our buttons from the view
oneJokeBtn = findViewById(R.id.joke_1);
threeJokesBtn = findViewById(R.id.joke_3);
// Register the onClick listener
oneJokeBtn.setOnClickListener(buttonHandler);
threeJokesBtn.setOnClickListener(buttonHandler);
// Declaring the Spinner
Spinner spinner = findViewById(R.id.spinner);
// Create an ArrayAdapter using the string array and a default spinner layout
ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this,
R.array.length_array, android.R.layout.simple_spinner_item);
// Specify the layout to use when the list of choices appears
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
// Apply the adapter to the spinner
spinner.setAdapter(adapter);
// Spinner onItemSelector implemented in the OnCreate Method
spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
switch (position){
case 0:
Toast.makeText(parent.getContext(), R.string.short_toast, Toast.LENGTH_SHORT).show();
break;
case 1:
Toast.makeText(parent.getContext(), R.string.medium_toast, Toast.LENGTH_SHORT).show();
break;
case 2:
Toast.makeText(parent.getContext(), R.string.long_toast, Toast.LENGTH_SHORT).show();
break;
}
}
@Override
public void onNothingSelected(AdapterView<?> parent) {
}
});
}
/** AsyncTask that reads one joke directly from the URL and adds it to the textView */
private class Download1JokeAsyncTask extends AsyncTask<Void, Void, String> {
private ProgressDialog progressDialog;
@Override
protected void onPreExecute() {
progressDialog = new ProgressDialog(getApplicationContext());
progressDialog.setMessage(getString(R.string.progress_msg));
progressDialog.setIndeterminate(true);
progressDialog.show();
}
@Override
protected String doInBackground(Void... voids) {
try {
URL url = new URL("http://www.oracle.com/");
URLConnection conn = url.openConnection();
// Obtain the input stream
BufferedReader in = new BufferedReader(new InputStreamReader(conn.getInputStream()));
// The joke is a one liner, so just read one line.
String joke;
while ((joke = in.readLine()) != null) {
System.out.println(joke);
}
// Close the connection
in.close();
} catch (MalformedURLException e) {
e.printStackTrace();
Log.e(ERROR_TAG, "Exception: ", e);
} catch (IOException e) {
e.printStackTrace();
Log.e(ERROR_TAG, "Exception: ", e);
}
return null;
}
@Override
protected void onPostExecute(String joke) {
mJokeTv.setText(joke);
if (progressDialog.isShowing()) {
progressDialog.dismiss();
}
}
}
/** AsyncTask that reads three jokes directly from the URL and adds it to the textView */
private class Download3JokeAsyncTask extends AsyncTask<Void, Integer, String[]> {
private ProgressDialog mProgressDialog;
@Override
protected void onPreExecute() {
super.onPreExecute();
mProgressDialog = new ProgressDialog(getApplicationContext());
mProgressDialog.setProgress(0);
mProgressDialog.setIndeterminate(false);
mProgressDialog.show();
}
@Override
protected String[] doInBackground(Void... voids) {
int count = 2;
for (int i = 0; i < 2; i++){
try {
URL url = new URL("http://www.oracle.com/");
URLConnection conn = url.openConnection();
// Obtain the input stream
BufferedReader in = new BufferedReader(new InputStreamReader(conn.getInputStream()));
// The joke is a one liner, so just read one line.
String joke;
while ((joke = in.readLine()) != null) {
System.out.println(joke);
}
// Close the connection
in.close();
} catch (MalformedURLException e) {
e.printStackTrace();
Log.e(ERROR_TAG, "Exception: ", e);
} catch (IOException e) {
e.printStackTrace();
Log.e(ERROR_TAG, "Exception: ", e);
}
publishProgress((int) ((i / (float) count) * 100));
}
return null;
}
@Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
}
@Override
protected void onPostExecute(String[] strings) {
super.onPostExecute(strings);
}
}
/** onClickListener that gets the id of the button pressed and download jokes accordingly */
OnClickListener buttonHandler = new OnClickListener() {
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.joke_1:
new Download1JokeAsyncTask().execute();
break;
case R.id.joke_3:
new Download3JokeAsyncTask().execute();
break;
}
}
};
这里是LogCat的日志：
--------- beginning of crash
04-14 18:57:10.670 17411-17411/com.mad.exercise4 E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.mad.exercise4, PID: 17411
android.view.WindowManager$BadTokenException: Unable to add window -- token null is not valid; is your activity running?
at android.view.ViewRootImpl.setView(ViewRootImpl.java:765)
at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:356)
at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:93)
at android.app.Dialog.show(Dialog.java:330)
at com.mad.exercise4.MainActivity$Download3JokeAsyncTask.onPreExecute(MainActivity.java:136)
at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:648)
at android.os.AsyncTask.execute(AsyncTask.java:595)
at com.mad.exercise4.MainActivity$2.onClick(MainActivity.java:187)
at android.view.View.performClick(View.java:6294)
at android.view.View$PerformClick.run(View.java:24770)
at android.os.Handler.handleCallback(Handler.java:790)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6494)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
04-14 18:57:10.721 17411-17416/com.mad.exercise4 I/zygote: Do full code cache collection, code=92KB, data=56KB
After code cache collection, code=90KB, data=44KB
----------
我没有填充第二个AsyncTask代码，因为它也会导致相同的错误。
请帮助:)。
答案 0 :(得分：1)
尝试使用
progressDialog = new ProgressDialog(MainActivity.this);
而不是
progressDialog = new ProgressDialog(getApplicationContext());
答案 1 :(得分：0)
您需要替换
/search/?name=moviename带
mProgressDialog = new ProgressDialog(getApplicationContext());
参考：