编辑文本第一次输入一个字母验证 [英] Edit text first time to input a letter validation

问题描述

我创建如果用户输入一个字母或数字，然后一个按钮，将弹出来检查应用程序。如果用户没有输入一个字母一个验证将显示。

I'm creating an application that checks if the user inputs a letter or a number then a button will pop-out. And if the user didn't enter a single letter a validation will show.

这里是我想要调试[主要活动的例子。 PS。不是我真正的code]：

Here's an example of what I'm trying to debug[main activity. PS. not my real code]:

private EditText edittext;

    Button checkBtn;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        addKeyListener();
    }

    public void addKeyListener() {
        edittext = (EditText) findViewById(R.id.editText);
        checkBtn = (Button) findViewById(R.id.button1);

        checkBtn.setVisibility(View.INVISIBLE);


        edittext.setOnKeyListener(new OnKeyListener() {
            public boolean onKey(View v, int keyCode, KeyEvent event) {


                if ((event.getAction() == KeyEvent.ACTION_DOWN)
                        && (keyCode == KeyEvent.KEYCODE_ENTER)) {

                    checkBtn.setVisibility(View.VISIBLE);

                    return true;

                else if ((event.getAction() == KeyEvent.ACTION_DOWN)
                    && (keyCode == KeyEvent.KEYCODE_9)) {

                // display a floating message
                Toast.makeText(MyAndroidAppActivity.this,
                        "Number 9 is pressed!", Toast.LENGTH_LONG).show();
                return true;
            }

            return false;
}
        });

    }
}

问题：
有没有一种方法可以自动使按钮显示当用户键入不点击回车键的信。如果用户没有输入一个字母一个验证会弹出说无效，该按钮将不会显示。

Question: Is there a way to make the button show automatically when a user types a letter without clicking the enter key. And if the user didn't input a letter a validation will pop out saying invalid and the button will not display.

我试图寻找正确的答案，但仍然我找不到它。

I tried looking for the right answer but still I couldn't find it.

推荐答案

您，我的朋友，需要

EditText editText = (EditText)findViewById(R.id.edittext);
editText .addTextChangedListener(new TextWatcher() {

        @Override
        public void afterTextChanged(Editable s) {
            ; //Do nothing
        }

        @Override
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {
            ; //Do nothing
        }

        @Override
        public void onTextChanged(CharSequence s, int start, int before, int count) {
            //TODO put your code here.
        } 

    });

现在，只是检查，看看是否能S字符序列中包含了你的信，你会用自己的方式。

Now, just check to see if that "s" Char Sequence contains your letter and you'll be on your way.

编辑：
一旦你的CharSequence的，只是请检查的第一个字符是字母。

Once you have that CharSequence, just check to see that the first char is a letter.

要得到第一个字符，执行

To get the first char, do

s.charAt(0);  //Note: if there is nothing here, it could throw a null pointer.

Character类具有您可以用它来看看它是否是一个字母（或数字，大写，小写字母，数字，数字或字母等），称为静态函数

The Character class has a static function that you can use to see if it is a letter (or a number, capital, lowercase, digit, digit or letter, etc) called

Character.isLetter(char); 

所以你可以不喜欢

so you could do something like

        public void onTextChanged(CharSequence s, int start, int before, int count) {
            //Check to see that there is at least 1 char to look at.
            //Then check to see if it is a letter.
            //(Note: the && is AND, so both things have to be true)
            if (s.length() > 0 && Character.isLetter(s.charAt(0))) {
                ; //Display your button
            } else { 
                ; //Display your error
            }
        }

帮助吗？

您可以创建一个名为MyTextWatcher新类（无论是在它自己的文件，你可以在任何地方或一个类（如果所有编辑的文本都在同一区域）内的类导入它），然后里面做常规的东西，你现在是在专家：

You can create a new class called MyTextWatcher (either in it's own file where you can import it anywhere or as a class within a class (if all of the edit texts are in the same area)), and then inside there do the regular stuff you are now expert at:

public class MyTextWatcher implements TextWatcher {
    @Override
    public void beforeTextChanged(CharSequence s, int start, int count, int after) {
    }
    @Override
    public void onTextChanged(CharSequence s, int start, int before, int count) {
    }
    @Override
    public void afterTextChanged(Editable s) {  
    }
}

我个人preFER做它包含的EditText类里面，但它可以在一个单独的文件中去（即导入），然后是更多的重用。而如果因为任何原因，你需要用TextWatcher访问的东西，你可以将它们作为一个构造函数。做类里面的东西的好处是，你没有的东西传递到构造函数。这只是为你做的事情少。但这里是一个构造函数的例子...

I personally prefer doing it inside the class that contains the edittext, but it can go in a separate file (that you import) and then it's more reusable. And if for any reason, you need to access things with your TextWatcher, you can pass them in as a constructor. The advantage of doing things inside the class is that you don't have to pass things into a constructor. It's just less things for you to do. But here is an example of that constructor...

public class MyTextWatcher implements TextWatcher {
    private Thing1 mThing1;
    private Thing2 mThing2;
    public MyTextWatcher(Thing1 t1, Thing2 t2) {
        mThing1 = t1;
        mThing2 = t2;
    }
    ...
}

请注意：做时只是要小心不要相互连接的东西太多了。它可能会很麻烦以后。 ：）

Note: Just be careful not to interlink things too much when doing that. It can get hairy later on. :)

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