我有 MainActivity 类和单独的 AsyncTask 类,它们是我从我的主要 Activity 类中执行的。我正在尝试在 Main Activity 布局上显示对话框,该布局应从 AsyncTask 类的 onPreExecute 方法调用。
我正在尝试实现此代码,主布局上没有显示对话框,应用程序停止。 请帮助:)
代码是这样的
主 Activity 类
public class MainActivity extends Activity implements LoginResponse {
public static Context context_main;
LoginThread login = new LoginThread(context_main);
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
login.execute();
}
.
.
.
}
和 LoginThread 类
public class LoginThread extends AsyncTask<Void, Void, RequestToken> {
.
.
.
public LoginThread(Context context)
{
this.context= context;
}
protected void onPreExecute()
{
super.onPreExecute();
pDialog = new ProgressDialog(context);
pDialog.setMessage(Html.fromHtml("<b>Logging In</b><br/>Please wait..."));
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show();
}
.
.
.
}
这是 logcat 消息
03-12 15:02:10.838: E/Error(32517): I got error
03-12 15:02:10.838: E/Error(32517): java.lang.NullPointerException
03-12 15:02:10.838: E/Error(32517): at android.app.AlertDialog.resolveDialogTheme(AlertDialog.java:143)
03-12 15:02:10.838: E/Error(32517): at android.app.AlertDialog.<init>(AlertDialog.java:98)
03-12 15:02:10.838: E/Error(32517): at android.app.ProgressDialog.<init>(ProgressDialog.java:77)
03-12 15:02:10.838: E/Error(32517): at pack.locationinfo.LoginThread.onPreExecute(LoginThread.java:87)
03-12 15:02:10.838: E/Error(32517): at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:586)
03-12 15:02:10.838: E/Error(32517): at android.os.AsyncTask.execute(AsyncTask.java:534)
03-12 15:02:10.838: E/Error(32517): at pack.locationinfo.MainActivity.TwitterLogin(MainActivity.java:53)
03-12 15:02:10.838: E/Error(32517): at java.lang.reflect.Method.invokeNative(Native Method)
03-12 15:02:10.838: E/Error(32517): at java.lang.reflect.Method.invoke(Method.java:525)
03-12 15:02:10.838: E/Error(32517): at android.view.View$1.onClick(View.java:3833)
03-12 15:02:10.838: E/Error(32517): at android.view.View.performClick(View.java:4475)
03-12 15:02:10.838: E/Error(32517): at android.view.View$PerformClick.run(View.java:18784)
03-12 15:02:10.838: E/Error(32517): at android.os.Handler.handleCallback(Handler.java:730)
03-12 15:02:10.838: E/Error(32517): at android.os.Handler.dispatchMessage(Handler.java:92)
03-12 15:02:10.838: E/Error(32517): at android.os.Looper.loop(Looper.java:137)
03-12 15:02:10.838: E/Error(32517): at android.app.ActivityThread.main(ActivityThread.java:5414)
03-12 15:02:10.838: E/Error(32517): at java.lang.reflect.Method.invokeNative(Native Method)
03-12 15:02:10.838: E/Error(32517): at java.lang.reflect.Method.invoke(Method.java:525)
03-12 15:02:10.838: E/Error(32517): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1187)
03-12 15:02:10.838: E/Error(32517): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)
03-12 15:02:10.838: E/Error(32517): at dalvik.system.NativeStart.main(Native Method)
03-12 15:02:16.108: D/mali_winsys(32517): new_window_surface returns 0x3000
最佳答案
导致崩溃的这一行......在这里,context_main
是 null
。
LoginThread login = new LoginThread(context_main);
现在,在 onCreate()
方法中初始化 LoginThread
对象,如下所示...发生崩溃是因为 Context
MainActivity
未正确分配。
LoginThread login;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
login = new LoginThread(this);
}
关于java - 从 AsyncTask 类调用的 MainActivity 上不显示对话框,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/22347651/