android - 如何处理来自 EditText 的华氏温度并打印其对应的摄氏温度？

Question

我对在 Android 中创建监听器的概念感到困惑。我的程序的目的很简单:在单位之间进行转换(例如华氏度到摄氏度，摄氏度到华氏度等)。如何获取 EditText 对象中的文本，然后如何将其打印出来？每次运行时我都会收到错误消息(不幸的是，Converter.exe 已停止。)这是我目前的代码。请指教。

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class ConverterActivity extends Activity
{
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    Button button = (Button) findViewById(R.id.temp_Button);
    button.setOnClickListener(new View.OnClickListener() 
    {
        public void onClick(View v)
        {
            setContentView(R.layout.body);
        }
    });  

    Button ok = (Button) findViewById(R.id.OK_Button);
    ok.setOnClickListener(new View.OnClickListener() 
    {
        public void onClick(View v)
        {
            EditText et = (EditText) getText(0);
            final int num = Integer.parseInt(et.toString());
            double answer = (num - 32) * 5/9;
            TextView tv = (TextView) findViewById(R.id.editText);
            tv.setText(Double.toString(answer));
        }
    });

}
}

我还有两个布局 (.xml) 文件(我不确定这是否是正确的编程风格)。

main 仅显示可以单击的按钮。然后，单击按钮后出现第二个 .xml 文件。

主.xml

<?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >

<Button
    android:id="@+id/temp_Button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/F" />
 <Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/C" />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/I" />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/Cm" />

 </LinearLayout>

body.xml(第二个)-

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="vertical" >

<TextView
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:text="Enter temperature:" />

<EditText
    android:id="@+id/editText"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:background="@android:drawable/editbox_background"
    android:digits="1, 2, 3, 4, 5, 6, 7, 8, 9" />

<Button
    android:id="@+id/cancel_Button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Cancel" />

<Button
    android:id="@+id/OK_Button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="OK" />

 </LinearLayout>

重申一下，我的问题出现在这段代码中:

 Button ok = (Button) findViewById(R.id.OK_Button);
   ok.setOnClickListener(new View.OnClickListener() 
   {
       public void onClick(View v)
        {
            EditText et = (EditText) getText(0);
            final int num = Integer.parseInt(et.toString());
            double answer = (num - 32) * 5/9;
           TextView tv = (TextView) findViewById(R.id.editText);
           tv.setText(Double.toString(answer));
        }
   });

目的是从用户输入的 EditText 对象中获取数字，将其转换并打印出来，但我不确定我这样做是否正确，或者是否正确地方。

**更新:这是日志。

02-06 19:53:36.148: D/AndroidRuntime(529): Shutting down VM
02-06 19:53:36.158: W/dalvikvm(529): threadid=1: thread exiting with uncaught exception (group=0x409c01f8)
02-06 19:53:36.168: E/AndroidRuntime(529): FATAL EXCEPTION: main
02-06 19:53:36.168: E/AndroidRuntime(529): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.sapra.converter/com.sapra.converter.ConverterActivity}: java.lang.NullPointerException
02-06 19:53:36.168: E/AndroidRuntime(529):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
02-06 19:53:36.168: E/AndroidRuntime(529):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
02-06 19:53:36.168: E/AndroidRuntime(529):  at android.app.ActivityThread.access$600(ActivityThread.java:123)
02-06 19:53:36.168: E/AndroidRuntime(529):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
02-06 19:53:36.168: E/AndroidRuntime(529):  at android.os.Handler.dispatchMessage(Handler.java:99)
02-06 19:53:36.168: E/AndroidRuntime(529):  at android.os.Looper.loop(Looper.java:137)
02-06 19:53:36.168: E/AndroidRuntime(529):  at android.app.ActivityThread.main(ActivityThread.java:4424)
02-06 19:53:36.168: E/AndroidRuntime(529):  at java.lang.reflect.Method.invokeNative(Native Method)
02-06 19:53:36.168: E/AndroidRuntime(529):  at java.lang.reflect.Method.invoke(Method.java:511)
02-06 19:53:36.168: E/AndroidRuntime(529):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
02-06 19:53:36.168: E/AndroidRuntime(529):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
02-06 19:53:36.168: E/AndroidRuntime(529):  at dalvik.system.NativeStart.main(Native Method)
02-06 19:53:36.168: E/AndroidRuntime(529): Caused by: java.lang.NullPointerException
02-06 19:53:36.168: E/AndroidRuntime(529):  at com.sapra.converter.ConverterActivity.onCreate(ConverterActivity.java:29)
02-06 19:53:36.168: E/AndroidRuntime(529):  at android.app.Activity.performCreate(Activity.java:4465)
02-06 19:53:36.168: E/AndroidRuntime(529):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
02-06 19:53:36.168: E/AndroidRuntime(529):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
02-06 19:53:36.168: E/AndroidRuntime(529):  ... 11 more

Answer 1

这很简单，我想你可以从这里弄明白。

// This is the TextView you set in your layout. It will display the temperature.
    final TextView tv = (TextView) findViewById(R.id.tv);

    // This sets up the EditText so you can capture the input and return the temperature.
    final EditText edittext = (EditText) findViewById(R.id.et);
    edittext.setOnKeyListener(new OnKeyListener() {
        public boolean onKey(View v, int keyCode, KeyEvent event) {
            // If the event is a key-down event on the "enter" button
            if ((event.getAction() == KeyEvent.ACTION_DOWN)
                    && (keyCode == KeyEvent.KEYCODE_ENTER)) {
                // Perform action on key press
                float f = Float.parseFloat(edittext.getText().toString());
                tv.setText(String.valueOf(convertCelciusToFahrenheit(f)));
                return true;
            }
            return false;
        }
    });

}

// Converts to celcius
private float convertFahrenheitToCelcius(float fahrenheit) {
    return ((fahrenheit - 32) * 5 / 9);
}

// Converts to fahrenheit
private float convertCelciusToFahrenheit(float celsius) {
    return ((celsius * 9) / 5) + 32;
}