Java 当您调用异步任务的方法时,应用程序将退出
我有个问题。我正在尝试创建Activity cause asynchronous task,并在执行创建适配器的被调用方法adapterCreate()class Profile.class之后创建。必须在方法的第一个参数中传输上下文。这里,例如,如果我在线上调用类中的一个方法,如果transfer contex为“this”,则所有方法都可以正常工作。如果我从异步任务调用,应用程序将退出。我不知道该怎么办。我希望得到你的帮助。谢谢大家! Profile.classJava 当您调用异步任务的方法时,应用程序将退出,java,android,android-activity,android-context,Java,Android,Android Activity,Android Context,我有个问题。我正在尝试创建Activity cause asynchronous task,并在执行创建适配器的被调用方法adapterCreate()class Profile.class之后创建。必须在方法的第一个参数中传输上下文。这里,例如,如果我在线上调用类中的一个方法,如果transfer contex为“this”,则所有方法都可以正常工作。如果我从异步任务调用,应用程序将退出。我不知道该怎么办。我希望得到你的帮助。谢谢大家! Profile.class public class P
public class Profile extends AppCompatActivity {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_application);
new ParseTask(this).execute();
}
public void adapterCreate(Activity context){
String[] str1 = {"mesages1", "messages2"};
String[] str2 = {"photo1", "photo2"};
String[] str3 = {"name1", "name2"};
adapter = new LazyAdapter(context, str1, str2, str3);
list.setAdapter(adapter);
}
}
public class ParseTask extends AsyncTask<Void, Void, String> {
HttpURLConnection urlConnection = null;
BufferedReader reader = null;
String resultJson = "";
Activity act;
public ParseTask (Activity context){
this.act = context;
}
@Override
protected String doInBackground(Void... params) {
try {
URL url = new URL("/friends.json");
urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setRequestMethod("GET");
urlConnection.connect();
InputStream inputStream = urlConnection.getInputStream();
StringBuffer buffer = new StringBuffer();
reader = new BufferedReader(new InputStreamReader(inputStream));
String line;
while ((line = reader.readLine()) != null) {
buffer.append(line);
}
resultJson = buffer.toString();
} catch (Exception e) {
e.printStackTrace();
}
return resultJson;
}
@Override
protected void onPostExecute(String strJson) {
super.onPostExecute(strJson);
new Profile().chatCreate();
}
}
public class LazyAdapter extends BaseAdapter {
private Activity activity;
private String[] messages;
private String[] photo;
private String[] name;
private static LayoutInflater inflater=null;
//public ImageLoader imageLoader;
public LazyAdapter(Activity a, String[] messages_c, String[] photo_c, String[] name_c) {
activity = a;
messages=messages_c;
photo = photo_c;
name = name_c;
inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
//imageLoader=new ImageLoader(activity.getApplicationContext());
}
public int getCount() {
return name.length;
}
public Object getItem(int position) {
return position;
}
public long getItemId(int position) {
return position;
}
public View getView(int position, View convertView, ViewGroup parent) {
View vi=convertView;
if(convertView==null) vi = inflater.inflate(R.layout.listview_row, null);
TextView name_c = (TextView)vi.findViewById(R.id.name_c);
TextView content_c = (TextView)vi.findViewById(R.id.content_c);
ImageView image = (ImageView)vi.findViewById(R.id.image);
name_chat.setText(name[position]);
content_chat.setText(messages[position]);
return vi;
}
}
ParseTask.class
public class Profile extends AppCompatActivity {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_application);
new ParseTask(this).execute();
}
public void adapterCreate(Activity context){
String[] str1 = {"mesages1", "messages2"};
String[] str2 = {"photo1", "photo2"};
String[] str3 = {"name1", "name2"};
adapter = new LazyAdapter(context, str1, str2, str3);
list.setAdapter(adapter);
}
}
public class ParseTask extends AsyncTask<Void, Void, String> {
HttpURLConnection urlConnection = null;
BufferedReader reader = null;
String resultJson = "";
Activity act;
public ParseTask (Activity context){
this.act = context;
}
@Override
protected String doInBackground(Void... params) {
try {
URL url = new URL("/friends.json");
urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setRequestMethod("GET");
urlConnection.connect();
InputStream inputStream = urlConnection.getInputStream();
StringBuffer buffer = new StringBuffer();
reader = new BufferedReader(new InputStreamReader(inputStream));
String line;
while ((line = reader.readLine()) != null) {
buffer.append(line);
}
resultJson = buffer.toString();
} catch (Exception e) {
e.printStackTrace();
}
return resultJson;
}
@Override
protected void onPostExecute(String strJson) {
super.onPostExecute(strJson);
new Profile().chatCreate();
}
}
public class LazyAdapter extends BaseAdapter {
private Activity activity;
private String[] messages;
private String[] photo;
private String[] name;
private static LayoutInflater inflater=null;
//public ImageLoader imageLoader;
public LazyAdapter(Activity a, String[] messages_c, String[] photo_c, String[] name_c) {
activity = a;
messages=messages_c;
photo = photo_c;
name = name_c;
inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
//imageLoader=new ImageLoader(activity.getApplicationContext());
}
public int getCount() {
return name.length;
}
public Object getItem(int position) {
return position;
}
public long getItemId(int position) {
return position;
}
public View getView(int position, View convertView, ViewGroup parent) {
View vi=convertView;
if(convertView==null) vi = inflater.inflate(R.layout.listview_row, null);
TextView name_c = (TextView)vi.findViewById(R.id.name_c);
TextView content_c = (TextView)vi.findViewById(R.id.content_c);
ImageView image = (ImageView)vi.findViewById(R.id.image);
name_chat.setText(name[position]);
content_chat.setText(messages[position]);
return vi;
}
}
logcat日志
09-24 16:49:10.821 7969-7969/package E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.NullPointerException
at package.Profile.chatCreate(Profile.java:645)
at package.ParseTask.onPostExecute(ParseTask.java:108)
at package.ParseTask.onPostExecute(ParseTask.java:21)
at android.os.AsyncTask.finish(AsyncTask.java:631)
at android.os.AsyncTask.access$600(AsyncTask.java:177)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4745)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
当你在一个活动中说
this
时,活动的上下文会被发送,但异步任务不是这样(这里this
指的是异步任务本身),因此你必须做的是yourActivity。这个你绝对不能这样做:
new Profile().chatCreate();
Profile
是一个活动
,它是一个Android组件。您不能使用new
自己实例化Android组件。只有Android框架可以实例化Android组件,因为它们需要先设置上下文
,然后才能使用
如果您想在活动
上调用一个方法,那么您需要使用已经由Android框架创建的活动
的实例。post logcat logAdded,请参阅。chatCreate()方法在哪里?我做什么?您的异步任务
由概要文件
类创建,它在构造函数中传递对自身的引用。只需将act
转换为Profile
并调用chatCreate()
,如下所示:((Profile)act.chatCreate()代码>。