android - 无法在android中正确实现textwatcher

Question

我正在寻找一种方法来找出用户在 EditText 中键入的内容，然后我偶然发现了 TextWatcher。问题是我不明白函数中的参数指的是什么。我想逐个字母地跟踪用户输入的文本。我不知道哪个参数是正确的下标号。我尝试了不同的变体，但都没有成功。

本质上，我想保存在数组中输入的文本，直到用户按下“,”按钮或超过 24 个字符的限制。请指教。

public class Main extends Activity implements OnClickListener {

    // inputans.setOnKeyListener(this);

    Button go;
    TextView answer;
    TextView check;
    EditText inputans, inputq;
    boolean done1 = false;
    char[] ans = new char[30];
    String predef = "Please answer my question";
    char[] predefc = predef.toCharArray();
    int len = predefc.length;
    int i = 0;
    char[] substring = new char[30];

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initialisevars();
        go.setEnabled(false);
        go.setOnClickListener(this);

        inputans.addTextChangedListener(new TextWatcher() {
            @Override
            public void onTextChanged(CharSequence s, int start, int before,
                    int count) {

                if ((count - before) > 0) {
                    char current = s.charAt(before);                   
                    if (current == '.' || i >= 24) { // 24 check
                        // ans[i]='\0';
                        // inputans.setText(predef,
                        // TextView.BufferType.EDITABLE);
                        check.setText(predef);
                        go.setEnabled(true);
                    } else {

                        ans[i] = current;
                        i++; // char[] substring = char[30]; back button
                                // problem,check if prev length - current length
                                // >0

                        int m;
                        for (m = 0; m <= i; m++) {
                            substring[m] = predefc[m];
                        }

                        check.setText(substring.toString());
                        // substring[m]='\0';
                        /*
                         * inputans.setText(substring.toString(),
                         * TextView.BufferType.EDITABLE);
                         */

                    }
                }

            }

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

                // TODO Auto-generated method stub
            }

            @Override
            public void afterTextChanged(Editable s) {
                // TODO Auto-generated method stub

            }
        });

    }

    private void initialisevars() {
        // TODO Auto-generated method stub
        go = (Button) findViewById(R.id.bGo);
        answer = (TextView) findViewById(R.id.tvAns);
        inputans = (EditText) findViewById(R.id.etTricky);
        inputq = (EditText) findViewById(R.id.etQues);
        check = (TextView) findViewById(R.id.textView1);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub
        switch (v.getId()) {
        case R.id.bGo: {

            answer.setText(ans.toString()); 

        }
            break;

        }
    }

}

Answer 1

在 Android 文档中，您可以阅读到:

public abstract void onTextChanged (CharSequence s, int start, int before, int count) Added in API level 1

This method is called to notify you that, within s, the count characters beginning at start have just replaced old text that had length before. It is an error to attempt to make changes to s from this callback.

这意味着:

• s 已经是一个修改过的文本(你可以得到它的长度，通过s.length())
• count 是已添加的字符数
• start 是添加新字符的位置
• before 是更改前的文本长度

基本上为了实现你想要的，我宁愿使用这种方法而不是数组:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    initialisevars();
    go.setEnabled(false);
    go.setOnClickListener(this);

    inputans.addTextChangedListener(new TextWatcher() {
        @Override
        public void onTextChanged(CharSequence s, int start, int before,
                int count) {

            if ((s.length() - before) > 0) {  // Check if text is longer than before changing
                char current = s.charAt(before);                   
                if (current == '.' || s.length() >= 24) {
                    check.setText(predef);
                    go.setEnabled(true);
                } else {
                    check.setText(s);
                }
            }

        }

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

            // TODO Auto-generated method stub
        }

        @Override
        public void afterTextChanged(Editable s) {
            // TODO Auto-generated method stub

        }
    });
}

就这么简单。