String上的contains（）和substring（）導致NullPointerException

Question

我正在嘗試讀取文本文件。 我想每行掃描該文本文件。 之后，將檢查每行是否包含EditText中的字符串。 我已經嘗試了contains()和substring() ，但它們都不起作用。 該文本文件的大小約為17MB。

public class MainActivity extends Activity {
    Button t;
    EditText tv;
    ArrayList<String> myStringArray1;
    ListView lv;
    ArrayAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        tv = (EditText) findViewById(R.id.editText1);
        lv = (ListView) findViewById(R.id.listView1);
        myStringArray1 = new ArrayList<String>();

        adapter = new ArrayAdapter(this, android.R.layout.simple_list_item_1,
            myStringArray1);
        lv.setAdapter(adapter);
        tv.addTextChangedListener(new TextWatcher() {
            public void afterTextChanged(Editable s) {
                myStringArray1.clear();
                String a = search(tv.getText().toString());
                // myStringArray1.add(tv.getText().toString());
                adapter.notifyDataSetChanged();
            }

            public void beforeTextChanged(CharSequence s, int start, int count,
                int after) {
            }

            public void onTextChanged(CharSequence s, int start, int before,
                int count) {
            }
        });
        tv.requestFocus();
    }

    String search(String text) {
        String everything;
        AssetManager am = this.getAssets();
        InputStream is = null;
        try {
            is = am.open("test.txt");
        } catch (IOException e) {
            // TODO Auto-generated catch block
            // tv.setText("eror");
            e.printStackTrace();
        }
        BufferedReader br = new BufferedReader(new InputStreamReader(is));
        try {
            StringBuilder sb = new StringBuilder();
            String line = null;
            try {
                line = br.readLine();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            while (line != null) {
                // sb.append(line);
                // sb.append(System.lineSeparator());
                try {
                    line = br.readLine();

                    if (line.substring(0, text.length()).equals(text)) {
                        myStringArray1.add(line);
                    }
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            //everything = sb.toString();
        } finally {
            try {
                br.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        return "";
    }

這是日志

  07-30 08:29:37.823: W/dalvikvm(17714): threadid=1: thread exiting with uncaught exception (group=0x40d2a9a8)
  07-30 08:29:37.825: E/AndroidRuntime(17714): FATAL EXCEPTION: main
  07-30 08:29:37.825: E/AndroidRuntime(17714): java.lang.NullPointerException
  07-30 08:29:37.825: E/AndroidRuntime(17714):  at com.example.cantonese.MainActivity.search(MainActivity.java:98)
  07-30 08:29:37.825: E/AndroidRuntime(17714):  at com.example.cantonese.MainActivity$1.afterTextChanged(MainActivity.java:54)
  07-30 08:29:37.825: E/AndroidRuntime(17714):  at android.widget.TextView.sendAfterTextChanged(TextView.java:7291)
  07-30 08:29:37.825: E/AndroidRuntime(17714):  at android.widget.TextView$ChangeWatcher.afterTextChanged(TextView.java:8957)
  07-30 08:29:37.825: E/AndroidRuntime(17714):  at android.text.SpannableStringBuilder.sendAfterTextChanged(SpannableStringBuilder.java:970)
  07-30 08:29:37.825: E/AndroidRuntime(17714):  at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:497)
  07-30 08:29:37.825: E/AndroidRuntime(17714):  at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:435)
  07-30 08:29:37.825: E/AndroidRuntime(17714):  at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:30)
  07-30 08:29:37.825: E/AndroidRuntime(17714):  at android.view.inputmethod.BaseInputConnection.replaceText(BaseInputConnection.java:674)
  07-30 08:29:37.825: E/AndroidRuntime(17714):  at android.view.inputmethod.BaseInputConnection.setComposingText(BaseInputConnection.java:437)
  07-30 08:29:37.825: E/AndroidRuntime(17714):  at com.android.internal.view.IInputConnectionWrapper.executeMessage(IInputConnectionWrapper.java:333)
  07-30 08:29:37.825: E/AndroidRuntime(17714):  at com.android.internal.view.IInputConnectionWrapper$MyHandler.handleMessage(IInputConnectionWrapper.java:77)
  07-30 08:29:37.825: E/AndroidRuntime(17714):  at android.os.Handler.dispatchMessage(Handler.java:107)
  07-30 08:29:37.825: E/AndroidRuntime(17714):  at android.os.Looper.loop(Looper.java:194)
  07-30 08:29:37.825: E/AndroidRuntime(17714):  at android.app.ActivityThread.main(ActivityThread.java:5392)
  07-30 08:29:37.825: E/AndroidRuntime(17714):  at java.lang.reflect.Method.invokeNative(Native Method)
  07-30 08:29:37.825: E/AndroidRuntime(17714):  at java.lang.reflect.Method.invoke(Method.java:525)
  07-30 08:29:37.825: E/AndroidRuntime(17714):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
  07-30 08:29:37.825: E/AndroidRuntime(17714):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
  07-30 08:29:37.825: E/AndroidRuntime(17714):  at dalvik.system.NativeStart.main(Native Method)

兩種方法都導致相同的異常。

Answer 1

正如Mike和Peter告訴您的那樣，您應該刪除這兩行readline()行。 您嘗試子字符串化的第一行始終是第二行（可能不是您要找的內容）。

您可以使用while ((line = br.readLine()) != null)來while ((line = br.readLine()) != null)生活。

例如：

        StringBuilder sb = new StringBuilder();
        String line = null;
        try {
            while ((line = br.readLine()) != null)
                // sb.append(line);
                // sb.append(System.lineSeparator());
                if (line.substring(0, text.length()).equals(text)) {
                    myStringArray1.add(line);
                }
            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }