java - 如何使用TextWatcher自动从edittext中获取值并相乘？

Question

当我在编辑文本中输入数字时，应用程序强制关闭。我希望应用程序在输入值时自动计算 BMI，而无需按按钮。

我对 TextWatcher 一无所知，但我研究并提出了这段代码。但它不起作用。有什么问题吗？

public class BodyMassIndex extends Activity implements View.OnClickListener,
    TextWatcher {

double result;
EditText age, height, weight;
ToggleButton sex, cmin, kglb;
TextView tvResult;
double heightInt = 1;
double weightInt = 0;
int ageInt;

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.bmi);
    initialize();

    sex.setOnClickListener(this);
    cmin.setOnClickListener(this);
    kglb.setOnClickListener(this);


}

private void initialize() {
    // TODO Auto-generated method stub

    age = (EditText) findViewById(R.id.etAge);
    height = (EditText) findViewById(R.id.etHeight);
    weight = (EditText) findViewById(R.id.etWeight);
    sex = (ToggleButton) findViewById(R.id.tbSex);
    cmin = (ToggleButton) findViewById(R.id.tbCMIN);
    kglb = (ToggleButton) findViewById(R.id.tbKGLB);
    tvResult = (TextView) findViewById(R.id.tvResult);
    age.addTextChangedListener(this);
    height.addTextChangedListener(this);
    weight.addTextChangedListener(this);
}

@Override
public void onClick(View v) {
    // TODO Auto-generated method stub

    switch (v.getId()) {
    case R.id.tbCMIN:
        heightInt = heightInt * 0.0254;
        break;
    case R.id.tbKGLB:
        weightInt = weightInt * 0.45359237;
        break;
    }

}

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

private void calculate() {
    // TODO Auto-generated method stub
     Editable H = height.getText(), W = weight.getText();

    if(H != null)
        heightInt = Double.parseDouble(H.toString());
    if (W != null)
        weightInt = Double.parseDouble(W.toString());

    result = weightInt / (heightInt * heightInt);
    String textResult = "Your BMI is " + result;
    tvResult.setText(textResult);
}

@Override
public void beforeTextChanged(CharSequence s, int start, int count,
        int after) {
    // TODO Auto-generated method stub


}

@Override
public void onTextChanged(CharSequence s, int start, int before, int count) {
    // TODO Auto-generated method stub

    }
}

'

Answer 1

来自http://developer.android.com/reference/android/text/TextWatcher.html关于 afterTextChanged 方法: "但要小心不要让自己陷入无限循环，因为你所做的任何更改都会导致该方法再次递归调用....你可以使用 setSpan(Object, int, int, int )在 onTextChanged(CharSequence, int, int, int) "