不幸的是，程序已停止

Question

很遗憾，程序已停止

我试图在 android 工作室计算年龄。它没有显示任何错误消息，但是当我单击“按钮”时，应用程序崩溃并显示 “不幸的是，Test1 已停止。”

为什么我的程序在编译过程中没有显示任何错误消息却崩溃了？

java代码如下

package android.example.com.test1;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;

import java.util.Calendar;
import java.util.GregorianCalendar;

public class MainActivity extends AppCompatActivity {

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


}

public void hi() {

    Calendar now = new GregorianCalendar(2016, 3, 1);
    Calendar cal = new GregorianCalendar(2016, 2, 28);

    int res = now.get(Calendar.YEAR) - cal.get(Calendar.YEAR);
    if ((cal.get(Calendar.MONTH) > now.get(Calendar.MONTH))
            || (cal.get(Calendar.MONTH) == now.get(Calendar.MONTH) && cal.get(Calendar.DAY_OF_MONTH) > now
            .get(Calendar.DAY_OF_MONTH))) {
        res--;
    }


    TextView s = (TextView) findViewById(R.id.message);
    s.setText(" " + res);
}

}

xml 代码如下：

  <?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="android.example.com.test1.MainActivity">

    <TextView
        android:id="@+id/message"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_below="@+id/message"
        android:onClick="hi"
        android:text="Button" />


</RelativeLayout>

Answer 1

您设置点击侦听器的签名有误，应该是

public void hi(View v){//...code}
//             ^^^^^^

From Docs

您在 android:onClick 属性中声明的方法必须具有如上所示的签名。具体来说，该方法必须：

成为public
Return无效
定义一个 View as its only parameter（这将是被点击的视图）

Answer 2

这是因为onClick方法必须使用接收视图作为参数的方法。

public void hi(View view) {

    Calendar now = new GregorianCalendar(2016, 3, 1);
    Calendar cal = new GregorianCalendar(2016, 2, 28);

    int res = now.get(Calendar.YEAR) - cal.get(Calendar.YEAR);
    if ((cal.get(Calendar.MONTH) > now.get(Calendar.MONTH))
            || (cal.get(Calendar.MONTH) == now.get(Calendar.MONTH) && cal.get(Calendar.DAY_OF_MONTH) > now
            .get(Calendar.DAY_OF_MONTH))) {
        res--;
    }


    TextView s = (TextView) findViewById(R.id.message);
    s.setText(" " + res);
}

另一种方法是投按钮，覆盖onClick方法调用hi()方法。为此，您需要删除 XML.

的 onClick 属性

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


    Button button  = (Button) findViewById(R.id.button);
    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            hi();
        }
    });
}

public void hi() {

    Calendar now = new GregorianCalendar(2016, 3, 1);
    Calendar cal = new GregorianCalendar(2016, 2, 28);

    int res = now.get(Calendar.YEAR) - cal.get(Calendar.YEAR);
    if ((cal.get(Calendar.MONTH) > now.get(Calendar.MONTH))
            || (cal.get(Calendar.MONTH) == now.get(Calendar.MONTH) && cal.get(Calendar.DAY_OF_MONTH) > now
            .get(Calendar.DAY_OF_MONTH))) {
        res--;
    }


    TextView s = (TextView) findViewById(R.id.message);
    s.setText(" " + res);
}

不幸的是，程序已停止

Unfortunately, program has stopped

java

crash

android

很遗憾，程序已停止