当getText为空时按下“=”按钮时应用程序崩溃-Android Studio

Question

09-08 07:58:32.915 137 26-13726/com.ruthadeaton.bld3.calculator
e/androidruntime：致命异常：main process:com.ruthadeaton.bld3.calculator.calculator，PID:13726 java.lang.numberformatexception:empty string
atsun.misc.floatingdecimal.readjavaformatstring(FloatingDecimal.java:1842)at sun.misc.floatingdecimal.parsefloat 26.在Android.view.view.performClick（view.java:346)，在Android.view.view.performClick（view.java:6597)，在Android.view.view.performClickInternal（view.java:6574)，在Android.view.view.access$3100(View.java:778)，在Android.view.view$performClick.run（view.java:25885)，在Android.os.handler.handleCallback（handler.java:873)，在read.java:6669)位于com.android.internal.os.runtimeInit$metho的java.lang.reflect.Method.invoke（本机方法）dandargsCaller.run（runtimeinit.java:493)，com.android.internal.os.zygoteinit.main(zygoteinit.java:858)

下面是我的代码：

buttonEqual.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        mValueTwo=Float.parseFloat(edt1.getText() + "");
            if (mAddition == true) {
                edt1.setText(mValueOne + mValueTwo + "");
                mAddition=false;
            }
            if (mSubtract == true) {
                edt1.setText(mValueOne - mValueTwo + "");
                mSubtract=false;
            }

            if (mMultiplication == true) {
               edt1.setText(mValueOne * mValueTwo + "");
               mMultiplication=false;
            }

            if (mDivision == true) {
                edt1.setText(mValueOne / mValueTwo + "");
                mDivision=false;
            }
        }
    });

button0.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        edt1.setText(edt1.getText() + "0");
    }
});

buttonAdd.setOnClickListener(new View.OnClickListener() {
   @Override
   public void onClick(View v) {
        mValueOne=Float.parseFloat(edt1.getText() + "");
        mAddition=true;
        edt1.setText(null);
    }
});

buttonSub.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        mValueOne=Float.parseFloat(edt1.getText() + "");
        mSubtract=true;
        edt1.setText(null);
    }
});

buttonMul.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        mValueOne=Float.parseFloat(edt1.getText() + "");
        mMultiplication=true;
        edt1.setText(null);
    }
});

buttonDivision.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        mValueOne=Float.parseFloat(edt1.getText() + "");
        mDivision=true;
        edt1.setText(null);
     }
});

Answer 1

我有一个计算器应用程序崩溃时，等于按钮被按下，没有任何东西在EditText它从文本。

因为您不验证来自用户的输入是否有效。显然，空字符串不是应用程序在NumberFormatExecption崩溃的原因。

如果我的edittext.settext（）中有一个“0”，那么当按下其他数字时，“0”会停留在它们的前面。

private boolean isValidNumber(String numberInString) {
    try {
        Float.parseFloat(numberInString);
        return true;
    } catch (NumberFormatException e) {
        return false;
    }
}

其次，每当用户按下算术运算符(+、-、*、/)或相等(=)时，应用程序将从EDT1中获取值。然后编写一个方法来做到这一点，以避免重复代码。

/**
 * Get current input from user and try parse it to a number.
 *
 * @return a number if input is valid, otherwise return null.
 */
private Float getInputValue() {
    Float possibleNumber = null;
    String numberInString = edt1.getText().toString();
    if (isValidNumber(numberInString)) {
        possibleNumber = Float.parseFloat(numberInString);
    }
    return possibleNumber;
}

第三，通过使用TextWatcher防止用户添加多个零数。

edt1.addTextChangedListener(new 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) {
        String content = s.toString();
        if (content.startsWith("0") && content.length() == 2 && Character.isDigit(content.charAt(1))) {
            edt1.setText(String.valueOf(content.charAt(1)));
            edt1.setSelection(1);
        }
    }
});

终于把它放在一起了。

public class MainActivity extends AppCompatActivity {

    // Your variables here
    ...

    // Make these two variables is Float instead of float.
    Float mValueOne;
    Float mValueTwo;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Your init view here
        ...

        edt1.addTextChangedListener(new 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) {
                String content = s.toString();
                if (content.startsWith("0") && content.length() == 2 && Character.isDigit(content.charAt(1))) {
                    edt1.setText(String.valueOf(content.charAt(1)));
                    edt1.setSelection(1);
                }
            }
        });

        buttonEqual.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mValueTwo = getInputValue();
                if (mValueOne == null || mValueTwo == null) {
                    // One of there or both of two values are not valid then do nothing.
                    return;
                }

                if (mAddition) {
                    edt1.setText(String.valueOf(mValueOne + mValueTwo));
                    mAddition = false;
                }

                if (mSubtract) {
                    edt1.setText(String.valueOf(mValueOne + mValueTwo));
                    mSubtract = false;
                }

                if (mMultiplication) {
                    edt1.setText(String.valueOf(mValueOne + mValueTwo));
                    mMultiplication = false;
                }

                if (mDivision) {
                    edt1.setText(String.valueOf(mValueOne + mValueTwo));
                    mDivision = false;
                }
            }
        });

        button0.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                edt1.setText(String.valueOf(edt1.getText().toString() + "0"));
                edt1.setSelection(edt1.getText().length());
            }
        });

        buttonAdd.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mValueOne = getInputValue();
                mAddition = true;
                edt1.setText(null);
            }
        });

        buttonSub.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mValueOne = getInputValue();
                mSubtract = true;
                edt1.setText(null);
            }
        });

        buttonMul.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mValueOne = getInputValue();
                mMultiplication = true;
                edt1.setText(null);
            }
        });

        buttonDivision.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mValueOne = getInputValue();
                mDivision = true;
                edt1.setText(null);
            }
        });
    }

    /**
     * Get current input from user and try parse it to a number.
     *
     * @return a number if input is valid, otherwise return null.
     */
    private Float getInputValue() {
        Float possibleNumber = null;
        String numberInString = edt1.getText().toString();
        if (isValidNumber(numberInString)) {
            possibleNumber = Float.parseFloat(numberInString);
        }
        return possibleNumber;
    }

    private boolean isValidNumber(String numberInString) {
        try {
            Float.parseFloat(numberInString);
            return true;
        } catch (NumberFormatException e) {
            return false;
        }
    }
}