对话框和edittext侦听器：setEnabled崩溃

Question

Hello I am going crazy to understand where is the problem in this dialog. I am trying to create one dialog with inside an edittext .. If the edittext is empty the positive button must be disabled else enabled. I wrote this code.

public class Example extends AlertDialog {

    AlertDialog.Builder builder;
    EditText mEditText;
    Context mContext;
    Button button;
    String text;

    protected Example(Context context) {
        super(context);
        // TODO Auto-generated constructor stub
        builder = new AlertDialog.Builder(context);
        this.mContext = context;
        mEditText = new EditText(mContext);
        builder.setView(mEditText);
        builder.setPositiveButton("Okay", null);
        builder.setNegativeButton("No", null);

        mEditText.addTextChangedListener(new TextWatcher() {

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {

                AlertDialog dialog = builder.create();

                text = mEditText.getText().toString();

                if(text.trim().length()>0) {

                    button = dialog.getButton(AlertDialog.BUTTON_POSITIVE);

                    if(button != null)
                    button.setEnabled(true);

                    else
                        button = dialog.getButton(AlertDialog.BUTTON_POSITIVE);
                        button.setEnabled(false);
                }

                else
                    button = dialog.getButton(AlertDialog.BUTTON_POSITIVE);
                    button.setEnabled(false);

            }

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

            }

            @Override
            public void afterTextChanged(Editable s) {

            }

        });

        builder.setTitle("Example Dialog");
        builder.create();
        builder.show();

    }
}

When i execute this code and write something in edittext i get NullPointerException at the else inside the if at this line button.setEnabled(false); Where is the problem?

Answer 1

The scope of if and else is only upto next statment. If you want to use more than one statement than enclose it in block. For example-

else
{
button = dialog.getButton(AlertDialog.BUTTON_POSITIVE);
button.setEnabled(false);
}

Answer 2

@Happy_New_Year is right. You are missing {} in else parts. If you don't put {}, then the only very next statement would be considered as the else part. The button.setEnabled(false); is outside of else block. So the button object is not being initialized here.

Answer 3

Problem is at text = mEditText.getText().toString();

when text is null null.toString(); will crash.

        @Override
        public void onTextChanged(CharSequence s, int start, int before, int count) {
            if (s != null)
            {
                if (s.length() > 0)
                {
                    dialog.getButton(Dialog.BUTTON_POSITIVE).setEnabled(true);
                }
                else {
                    dialog.getButton(Dialog.BUTTON_POSITIVE).setEnabled(false);
                }
            }

        }

Here is entire code that I used in my project

AlertDialog.Builder builder; // Declare Globally
AlertDialog dialog; // Declare Globally

    builder = new AlertDialog.Builder(this);

    builder.setCancelable(false);
    builder.setTitle("Add New Keyword");
    final EditText input = new EditText(this);
    input.setHint("Min 3 Chars");
    builder.setView(input);

    input.addTextChangedListener(new TextWatcher() {

        @Override
        public void onTextChanged(CharSequence s, int start, int before, int count) {
            if (s != null)
            {
                if (s.length() > 2)
                {
                    dialog.getButton(Dialog.BUTTON_POSITIVE).setEnabled(true);
                }
                else {
                    dialog.getButton(Dialog.BUTTON_POSITIVE).setEnabled(false);
                }
            }

        }

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

        @Override
        public void afterTextChanged(Editable s) {

        }
    });

    builder.setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int whichButton) {

            if (input != null)
            {
                System.out.println("Entered Text" + input.getText().toString().trim());
            }
        }
    });

    builder.setNegativeButton(android.R.string.cancel, new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int whichButton) {
            dialog.dismiss();
        }
    });

    dialog = builder.create();
    dialog.show();
    dialog.getButton(Dialog.BUTTON_POSITIVE).setEnabled(false);

}

Answer 4

The error is obviously in this line :-

        mEditText = new EditText(mContext);

By doing this, you have created a new object for an Edittext. We do such thing when we create a dynamic edittext or any other widget.

In a normal scenario, you need to pass a reference to your edittext which you must have given in a property called as "id" in an xml file for the edittext for example :-

 <EditText 
     android:id = "@+id/editText1"
     <!-- other properties-->
</EditText

and in your class, you need to do like this firstly :- mEditText = (EditText)findViewById(R.id.editText1);

I hope you got it now