java - 单击按钮后，Android Studio 应用程序不断崩溃

Question

我是 Java 的初学者，但我正在尝试构建练习，但遇到了这个问题。用户输入捐款，按下按钮，捐款的值(value)就会增加。我编写了整个代码，但是当我单击按钮添加到捐赠计数时，应用程序崩溃了。我遵循了我老师的所有教诲。我在 Activity 中创建了一个方法，在 ui 构建器中，我转到单击属性上的按钮并将其设置为该方法。它应该进行得很顺利，但每当我点击按钮时它就会崩溃。这是我将 onClick 属性设置为 computeDonation 的 Activity 。

public void computeDonation(View v){

    String addedText = ((EditText)findViewById(R.id.AmountText)).getText().toString();

    DonationModel donation = new DonationModel(addedText);
    String answer = donation.calcDonation();

    ((TextView)findViewById(R.id.totalText)).setText(answer);
}

这是模型:

String textAdded;
double addedDonation;

public DonationModel(String y) {
    textAdded = y;
}

public String calcDonation(){
    double counter = Double.parseDouble(textAdded);
    addedDonation += counter;

    Locale locale = new Locale("en", "CA");
    NumberFormat fmt = NumberFormat.getCurrencyInstance(locale);

    return fmt.format(addedDonation);

}

我什至尝试过不使用数字格式，只是为了看看它是否会发回 Activity ，但事实并非如此。顺便说一句，我在类里面使用的是旧版本的 android studio。

这是日志:

02-15 17:12:28.797 21619-21619/ca.roumani.donations E/AndroidRuntime: FATAL EXCEPTION: main Process: ca.roumani.donations, PID: 21619 java.lang.IllegalStateException: Could not execute method for android:onClick at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293) at android.view.View.performClick(View.java:5197) at android.view.View$PerformClick.run(View.java:20909) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:145) at android.app.ActivityThread.main(ActivityThread.java:5942) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194) Caused by: java.lang.reflect.InvocationTargetException at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288) at android.view.View.performClick(View.java:5197)  at android.view.View$PerformClick.run(View.java:20909)  at android.os.Handler.handleCallback(Handler.java:739)  at android.os.Handler.dispatchMessage(Handler.java:95)  at android.os.Looper.loop(Looper.java:145)  at android.app.ActivityThread.main(ActivityThread.java:5942)  at java.lang.reflect.Method.invoke(Native Method)  at java.lang.reflect.Method.invoke(Method.java:372)  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)  Caused by: java.lang.NumberFormatException: Invalid double: "" at java.lang.StringToReal.invalidReal(StringToReal.java:63) at java.lang.StringToReal.parseDouble(StringToReal.java:267) at java.lang.Double.parseDouble(Double.java:301) at ca.roumani.donations.DonationModel.calcDonation(DonationModel.java:20) at ca.roumani.donations.DonationActivity.computeDonation(DonationActivity.java:24) at java.lang.reflect.Method.invoke(Native Method)  at java.lang.reflect.Method.invoke(Method.java:372)  at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)  at android.view.View.performClick(View.java:5197)  at android.view.View$PerformClick.run(View.java:20909)  at android.os.Handler.handleCallback(Handler.java:739)  at android.os.Handler.dispatchMessage(Handler.java:95)  at android.os.Looper.loop(Looper.java:145)  at android.app.ActivityThread.main(ActivityThread.java:5942)  at java.lang.reflect.Method.invoke(Native Method)  at java.lang.reflect.Method.invoke(Method.java:372)  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194) 

Answer 1

您的 textAdded 似乎是一个空字符串，这会导致 NumberFormatException 并使您的应用程序崩溃。你可以做些什么来防止这种情况，是在解析之前检查你的 textAdded 是否不为空:

public String calcDonation() {
    if (TextUtils.isEmpty(textAdded)) {
        //textAdded is empty, so just return an empty String
        return "";
    }
    //We're sure that textAdded has a value, so we can try to parse it
    double counter = Double.parseDouble(textAdded);
    addedDonation += counter;

    Locale locale = new Locale("en", "CA");
    NumberFormat fmt = NumberFormat.getCurrencyInstance(locale);

    return fmt.format(addedDonation);
} 

或者只是阻止在用户在 EditText View 中输入值之前调用该方法:

public void computeDonation(View v){
    String addedText = ((EditText)findViewById(R.id.AmountText)).getText().toString();
    if (TextUtils.isEmpty(textAdded)) {
        Toast.makeText(context, "Please enter a valid number", Toast.LENGTH_SHORT).show();
    } else {
        DonationModel donation = new DonationModel(addedText);
        String answer = donation.calcDonation();
        ((TextView)findViewById(R.id.totalText)).setText(answer);
    }
}