为什么每次我实现这个逻辑时我的应用程序都会崩溃？

Question

There are multiple cardView in the App, and Click on each Card a new Intent is launched. Also before launching the Intent I am passing a puExtra along.

  final String label = holder.text_label.getText().toString().trim();

    holder.cardView.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if (position == 0 && label.equalsIgnoreCase("Alt. English")) {

                Intent intent = new Intent(context, ShowPDFActivity.class);
                intent.putExtra("AltE","AltE");
                context.startActivity(intent);

            }
        }
    });

And in my another Activity, I have created an Array of Titles, where i Have stored all the possible values which are received in this Activity.

 String[] title = {
            "AltE",
            "Alt.English2013"
    };

Now I am running a for Loop to see what value is received and accordingly perform the functions.

Intent intent = getIntent();
    for (int i = 0; i <= title.length; i++) {
        Log.e("Length ", String.valueOf(title.length));

        a1 = intent.getStringExtra(title[i]);

        if (a1.equalsIgnoreCase("AltE")) {

            String pdf = "https://www.researchgate.net/STUDIES.pdf";
            webView.loadUrl("http://docs.google.com/viewer?url=" + pdf);

            webView.setWebViewClient(new WebViewClient() {

                public void onPageFinished(WebView view, String url) {
                    // do your stuff here
                    progressbar.setVisibility(View.GONE);
                }
            });


        } else {
            Toast.makeText(this, "In Else", Toast.LENGTH_SHORT).show();
        }

But the App crashes with this Message :

     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equalsIgnoreCase(java.lang.String)' on a null object reference

What Am i Doing Wrong and how can this be Fixed ?

Answer 1

First reverse: from

if (a1.equalsIgnoreCase("AltE")) {

to

   if ("AltE".equalsIgnoreCase(a1)) {

because "AltE" will not be equal to null will make it stop crashing.

Also the reason for your crash is that getStringExtra returns default null and you are checking for each title, rather than just one. and so for the "Alt.English2013" you don't have a value, according to your story.