当短信空白时，App Force关闭

Question

我是一个新的Android程序员，我正在尝试制作"二次方程求解器应用程序"。用户必须在3个textedit-s中输入3个值，并且这些值存储在双打中。如果用户将输入之一留为空白，则应用程序将关闭。默认情况下，如何将所有值设置为0，因此该应用不会强制关闭？

public class MainActivity extends Activity {
EditText inputA, inputB, inputC;
TextView nrRoots, root1, root2, roots;
Button bStepByStep, calculate;
Double a, b, c, D, x1, x2, x, dRootNr;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    inputA = (EditText) findViewById(R.id.etParamA);
    inputB = (EditText) findViewById(R.id.etParamB);
    inputC = (EditText) findViewById(R.id.etParamC);
    nrRoots = (TextView) findViewById(R.id.tvNrRoots);
    root1 = (TextView) findViewById(R.id.tvRoot1);
    roots = (TextView) findViewById(R.id.tvRoots);
    root2 = (TextView) findViewById(R.id.tvRoot2);
    calculate = (Button) findViewById(R.id.bCalculate);
    bStepByStep = (Button) findViewById(R.id.bStepByStep);
    calculate.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View arg0) {
            a = Double.parseDouble(inputA.getText().toString());
            b = Double.parseDouble(inputB.getText().toString());
            c = Double.parseDouble(inputC.getText().toString());
            double D = Math.sqrt((b * b) - (4 * a * c));
            if (D == 0) {
                nrRoots.setText("The equation " + a + "x^2+" + b + "x+" + c
                        + "=0 has 1 distinct root.");
                x = ((-1) * b) / (2 * a);
                root1.setText("x=" + x);
                root2.setText("");
                roots.setText("");
            } else if (D > 0) {
                nrRoots.setText("The equation " + a + "x^2+" + b + "x+" + c
                        + "=0 has 2 distinct roots.");
                x1 = (((-1) * b) + D) / (2 * a);
                x2 = (((-1) * b) - D) / (2 * a);
                root1.setText("x1= " + x1);
                root2.setText("x2= " + x2);
            } else {
                nrRoots.setText("The equation " + a + "x^2+" + b + "x+" + c
                        + "=0 has no distinct roots.");
                root1.setText("");
                root2.setText("");
            }
        }
    });

Answer 1

这是 Double.parseDouble(..)的NPE。

创建此功能

public double getDouble(String str) {
    if (str != null) {
        if (str.equalsIgnoreCase("")) {
            return 0;
        } else {
            return Double.parseDouble(str);
        }
    } else {
        return 0;
    }
}

然后使用此代码

        a = getDouble(inputA.getText().toString());
        b = getDouble(inputB.getText().toString());
        c = getDouble(inputC.getText().toString());

Answer 2

在xml文件

中

android:text="0"
android:inputType="numeric" 

put" 0"为默认并制作数字输入类型以确保不会输入非数字。

以及

在解析之前进行控制，以防用户清除EditText。

if (!input.getText().toString().equals("")){
    //parse
}