编辑：

Question

我试图通过findViewById（）和SetVisiblity（）更改线性布局的可见性。但是当我调试时，我只看到空值。

请在onPostExecute（）方法中找到下面BackgroundMainActivity.java中的代码段。

我评论过它。请帮忙。

MainActivity.java

button_getUsername.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            BackgroundMainActivity backgroundMainActivity = new BackgroundMainActivity(MainActivity.this, v);
            backgroundMainActivity.execute("random", editText_username.getText().toString());
        }
    });

BackgroundMainActivity.java

public class BackgroundMainActivity extends AsyncTask<String, Void , String> {


    public BackgroundMainActivity(Context ct, View view) {
        context = ct;
        rootView = view;
    }

    @Override
    protected String doInBackground(String... params) {
        String login_URL = "some url";
        try {
            String username = params[1];

            URL url = new URL(login_URL);
            HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
            httpURLConnection.setRequestMethod("POST");
            httpURLConnection.setDoOutput(true);
            httpURLConnection.setDoOutput(true);

            OutputStream outputStream = httpURLConnection.getOutputStream();
            BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream,"UTF-8"));
            String postData = URLEncoder.encode("username","UTF-8")+"="+URLEncoder.encode(username,"UTF-8");
            bufferedWriter.write(postData);
            bufferedWriter.flush();
            bufferedWriter.close();
            outputStream.close();

            InputStream inputStream = httpURLConnection.getInputStream();
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream,"iso-8859-1"));

            result = bufferedReader.readLine();

            bufferedReader.close();
            inputStream.close();
            httpURLConnection.disconnect();
            return result;


        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
    @Override
    protected void onPreExecute(){

    }

    @Override
    protected void onPostExecute (String result){
        if(result.equals("success")){

//need to make this change
//LinearLayout someLayout = (LinearLayout)rootview.findViewById(R.id.layout_content);
//someLayout.setVisibility(View.VISIBLE);

            AlertDialog.Builder builder = new AlertDialog.Builder(context);
            builder.setMessage(result)
                    .setPositiveButton("Ok",null)
                    .show();
        }

    }

    @Override
    protected void onProgressUpdate(Void... values){
        super.onProgressUpdate(values);
    }
}

编辑：

activity_main.xml中

默认情况下，ss_layout_questions已消失。我希望在BackgroundMainActivity.java中将其显示为“result.equals（”success“）”。

 <?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    tools:context="com.xtremustechnologies.chotu.useractivity.MainActivity">

    <android.support.v4.widget.NestedScrollView
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:fillViewport="true"
        android:background="@color/lightGreen"
        android:layout_gravity="top">

        <LinearLayout
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:orientation="vertical">

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_alignParentTop="true"
                android:layout_centerHorizontal="true"
                android:orientation="vertical">

                <TextView
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_alignEnd="@+id/textviewr2"
                    android:layout_alignParentTop="true"
                    android:layout_centerHorizontal="true"
                    android:layout_gravity="center_horizontal"
                    android:layout_marginTop="30dp"
                    android:text="CHOTU"
                    android:textColor="@color/white"
                    android:textSize="40dp" />

                <TextView
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_centerHorizontal="true"
                    android:layout_gravity="center_horizontal"
                    android:layout_marginBottom="40dp"
                    android:text="Your Personal Assistant"
                    android:textColor="@color/white"
                    android:textSize="12dp" />
            </LinearLayout>

            <TextView
                android:id="@+id/ss_textview_questions"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_gravity="center_horizontal"
                android:layout_marginBottom="40dp"
                android:text="Security Questions "
                android:textColor="@color/black"
                android:textSize="20dp"
                android:visibility="gone"/>

            <EditText
                android:id="@+id/ss_et_username"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_centerHorizontal="true"
                android:layout_gravity="center_horizontal"
                android:hint="Enter Username" />

            <Button
                android:id="@+id/ss_button_getusername"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_below="@id/ss_et_username"
                android:layout_centerHorizontal="true"
                android:onClick="clickGetUsername"
                android:layout_gravity="center_horizontal"
                android:text="Submit" />

            <LinearLayout
                android:id="@+id/ss_layout_questions"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:orientation="vertical"
                android:visibility="gone">

                <LinearLayout
                    android:layout_width="fill_parent"
                    android:layout_height="wrap_content"
                    android:layout_below="@+id/textviewr3"
                    android:layout_centerHorizontal="false"
                    android:layout_marginLeft="40dp"
                    android:layout_marginRight="40dp"
                    android:orientation="horizontal">

                    <Button
                        android:id="@+id/ss_button_dob"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_gravity="left"
                        android:layout_marginRight="50dp"
                        android:text="Date of Birth" />

                    <TextView
                        android:id="@+id/ss_textView_dob"
                        android:layout_width="fill_parent"
                        android:layout_height="wrap_content"
                        android:layout_gravity="right|center_vertical|center_horizontal"
                        android:layout_weight="1"
                        android:text="TextView"
                        android:textSize="20dp" />
                </LinearLayout>

                <TextView
                    android:id="@+id/ss_textView_question1"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_marginLeft="20dp"
                    android:layout_marginRight="10dp"
                    android:layout_marginTop="30dp" />

                <EditText
                    android:id="@+id/ss_textView_ans1"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_marginLeft="20dp"
                    android:layout_marginTop="10dp"
                    android:hint="Enter your answer here" />

                <TextView
                    android:id="@+id/ss_textView_question2"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_marginLeft="20dp"
                    android:layout_marginRight="10dp"
                    android:layout_marginTop="30dp" />

                <EditText
                    android:id="@+id/ss_textView_ans2"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_marginLeft="20dp"
                    android:layout_marginTop="10dp"
                    android:hint="Enter your answer here" />

                <TextView
                    android:id="@+id/ss_textView_question3"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_marginLeft="20dp"
                    android:layout_marginRight="10dp"
                    android:layout_marginTop="30dp" />

                <EditText
                    android:id="@+id/ss_textView_ans3"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_marginLeft="20dp"
                    android:layout_marginTop="10dp"
                    android:hint="Enter your answer here" />

                <Button
                    android:id="@+id/ss_button_submit"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_gravity="center_horizontal"
                    android:background="@color/black"
                    android:text="Submit"
                    android:textColor="@color/white" />
            </LinearLayout>
        </LinearLayout>


    </android.support.v4.widget.NestedScrollView>
</android.support.constraint.ConstraintLayout>

Answer 1

终于工作了。这就是我做的事情

我在BackgroundMainActivity.java中添加了一个新类，然后在onPostExecute（）方法中调用它。

class a{

public Button button_reset, button_dob;
public LinearLayout layout_questions;
public TextView textView_title;
public EditText editText_username;

public void makeVisible(ForgotPasswordActivity context){

    LinearLayout layout_questions = (LinearLayout) context.findViewById(R.id.ss_layout_questions);
    layout_questions.setVisibility(View.VISIBLE);
}

BackgroundMainActivity.java中的onPostExecute（）

a obj = new a();
        obj.makeVisible((ForgotPasswordActivity) context);

Answer 2

是的，您应该收到NPE错误。为什么？因为看看这段代码：

button_getUsername.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        BackgroundMainActivity backgroundMainActivity = new BackgroundMainActivity(MainActivity.this, v);
        backgroundMainActivity.execute("random", editText_username.getText().toString());
    }
});

在这里，您尝试将Button（您的button_getUserName）传递给AsyncTask。然后，当您找到视图时，按钮中没有布局。

如何解决？实际上，它非常简单，只需在AsyncTask的构造函数中传递您的布局：

BackgroundMainActivity backgroundMainActivity = new BackgroundMainActivity(MainActivity.this, findViewById(R.id.layout_content));
// do on onPost:v.setVisibility...

AsyncTask，LinearLayout Android Update可见性

编辑：

2 个答案: