App crashes when adding View to layout when using int id Android SDK

Question

Basically, the point of the code is to interpret a String in a way that the View being created will be placed in the prior View mentioned.

% $- background:#000000 % 
Hello, World.
% $- background:#ffffff %
$+ id:test type:container %
Test

Here is the code for it.

new Thread() {
        StringBuilder text = new StringBuilder();
        @Override
        public void run() {
            try

            {
                String str = "";
                URL url = new URL("http://example.com/" + mes + "/" + mes + ".meb");
                BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));

                while ((str = in.readLine()) != null) {
                    text.append(str);
                }
                in.close();
            } catch (MalformedURLException e1)

            {
            }
            catch (IOException e)
            {
            }
            if(message.contains(".meb")) {
                String strn = text.toString().replace("\n", "").replace("\r", "");
                String str[] = strn.toString().split("%");
                int relative2 = 0;
                final int relative = relative2;
                for (final String l : str) {
                    String code[] = l.split(" ");
                    if (l.toString().contains("$-")) {
                        for(String p : code)
                        {
                            if(p.toString().contains("background"))
                            {
                                final String set[] = p.toString().split(":");
                                runOnUiThread(new Runnable() {
                                    @Override
                                    public void run() {
                                (findViewById(R.id.body)).setBackgroundColor(Color.parseColor(set[1]));
                                    }
                                });
                            }
                        }
                    }
                    else if(l.toString().contains("$+"))
                    {
                        String[] g = code[2].split(":");
                        String[] c = code[3].split(":");
                        final String[] test = {g[1], "100"};
                        globvar.add(test);
                        if(c[1].toString().equals("container")) {
                            runOnUiThread(new Runnable() {
                                @Override
                                public void run() {
                                    final LinearLayout element = new LinearLayout(getApplicationContext());
                                    element.setBackgroundColor(Color.parseColor("#FFFFFF"));
                                    element.setMinimumHeight(50);
                                    element.setId(Integer.parseInt(test[1]));
                                    ((LinearLayout) findViewById(relative)).addView(element);
                                }
                            });
                            relative2 = Integer.parseInt(test[1]);
                        }
                    }
                    else                        {

                        if(!l.toString().isEmpty()) {
                            runOnUiThread(new Runnable() {
                                @Override
                                public void run() {
                                    final TextView tv = new TextView(getApplicationContext());
                                    tv.setTextColor(Color.parseColor("#000000"));
                                    tv.setTextSize(18);
                                    tv.setText(l);
                                    ((LinearLayout) findViewById(relative)).addView(tv);
                                }
                            });
                        }
                    }
                }
            }
            else {
                if(message == null) {
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {

                        }
                    });
                }
            }
        }
    }.start();

When the app crashes, I get the following logcat error:

08-01 19:44:27.149 29893 29893 E AndroidRuntime: FATAL EXCEPTION: main

08-01 19:44:27.149 29893 29893 E AndroidRuntime: java.lang.NullPointerException

08-01 19:44:27.149 29893 29893 E AndroidRuntime:    at example.yemeb.List$1$3.run(List.java:116)

08-01 19:44:27.149 29893 29893 E AndroidRuntime:    at android.os.Handler.handleCallback(Handler.java:615)

08-01 19:44:27.149 29893 29893 E AndroidRuntime:    at android.os.Handler.dispatchMessage(Handler.java:92)

08-01 19:44:27.149 29893 29893 E AndroidRuntime:    at android.os.Looper.loop(Looper.java:137)

08-01 19:44:27.149 29893 29893 E AndroidRuntime:    at android.app.ActivityThread.main(ActivityThread.java:4931)

08-01 19:44:27.149 29893 29893 E AndroidRuntime:    at java.lang.reflect.Method.invokeNative(Native Method)

08-01 19:44:27.149 29893 29893 E AndroidRuntime:    at java.lang.reflect.Method.invoke(Method.java:511)

08-01 19:44:27.149 29893 29893 E AndroidRuntime:    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)

08-01 19:44:27.149 29893 29893 E AndroidRuntime:    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:558)

08-01 19:44:27.149 29893 29893 E AndroidRuntime:    at dalvik.system.NativeStart.main(Native Method)

This log shows that the error is occurring at ((LinearLayout) findViewById(relative)).addView(tv); at line 116.

What is the problem with my code?

Answer 1

Because of following code,

int relative2 = 0;
final int relative = relative2;

the value of relative is 0 which is final and can't be changed. So when you perform ((LinearLayout) findViewById(relative)), it becomes like ((LinearLayout) findViewById(0)). As there is no view associated with id 0, you don't get the reference to that view, hence the value is null. And when you try to add a view to it, you get a nullpointer exception.

Read findViewById() from docs.It says that

Finds a view that was identified by the id attribute from the XML that was processed in onCreate(Bundle).

Returns The view if found or null otherwise.

So basically in your case make sure when you try to find a view by id, the view is present in xml layout file with proper id assigned to it. So that when the R.java file is generated, this id will be mapped to an int value.