我使用TextUtils来做这个:

if (TextUtils.isEmpty(UsernameInfo.getText())) {
    validationError = true;
    validationErrorMessage.append(getResources().getString(R.string.error_blank_username));
}

如果editText为空，试试另一种简单的方法:

String star = editText.getText().toString();

if (star.equalsIgnoreCase("")) {
  Toast.makeText(getApplicationContext(), "Please Set start no", Toast.LENGTH_LONG).show();
}

如果EditText为空，为什么不禁用按钮呢?恕我直言，这看起来更专业:

        final EditText txtFrecuencia = (EditText) findViewById(R.id.txtFrecuencia);  
        final ToggleButton toggle = (ToggleButton) findViewById(R.id.toggleStartStop);
        txtFrecuencia.addTextChangedListener(new TextWatcher() {
        @Override
        public void afterTextChanged(Editable s) {
            toggle.setEnabled(txtFrecuencia.length() > 0);
        }

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

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

        }
       });

试试这个:

EditText txtUserName = (EditText) findViewById(R.id.txtUsername);
String strUserName = usernameEditText.getText().toString();
if (strUserName.trim().equals("")) {
    Toast.makeText(this, "plz enter your name ", Toast.LENGTH_SHORT).show();
    return;
}

或者像这样使用TextUtils类:

if(TextUtils.isEmpty(strUserName)) {
    Toast.makeText(this, "plz enter your name ", Toast.LENGTH_SHORT).show();
    return;
}

“看看这个，我相信你会喜欢的。”

log_in.setOnClickListener(new OnClickListener() {

    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub
        username=user_name.getText().toString();
        password=pass_word.getText().toString();
        if(username.equals(""))
        {
            user_name.setError("Enter username");
        }
        else if(password.equals(""))
        {
            pass_word.setError("Enter your password");
        }
        else
        {
            Intent intent=new Intent(MainActivity.this,Scan_QRActivity.class);
            startActivity(intent);
        }
    }
});

private boolean isEmpty(EditText etText) {
    if (etText.getText().toString().trim().length() > 0) 
        return false;

    return true;
}

或者和奥德修斯一样

  private boolean isEmpty(EditText etText) {
        return etText.getText().toString().trim().length() == 0;
    }

如果函数返回false表示编辑文本不为空，返回true表示编辑文本为空…