如何从EditText处理华氏温度并打印其相应的摄氏温度？

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（如华氏温度到摄氏温度，摄氏温度到华氏温度等）。如何获取EditText对象中的文本，然后如何将其打印出来？我每次运行时都会收到错误（不幸的是，Converter.exe已停止。）这是我的代码到目前为止。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));
        }
    });

}
}

我也有两个布局（.xml）文件（我不确定这是否是正确的编程风格）。

main只显示可以单击的按钮。然后，我点击按钮后出现第二个.xml文件。

main.xml中

<?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，转换它并将其打印出来，但我不确定我是否正确这样做，或者这是否在右边的地方。

**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;
}

Answer 2

仅作为一个例子。我前一段时间写过这个示例温度转换器。也许有人可能觉得它很有用。

---

public class TempTest extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        LinearLayout ll = new LinearLayout(this);           
        ll.setOrientation(1);
        Button b = new Button(this);
        b.setText("get temperature");
        b.setOnClickListener(new View.OnClickListener(){
            public void onClick(View view) {
                   getCelciusOrFarenheit();
            }
        });
        ll.addView(b);
        setContentView(ll);
    }

    public AlertDialog getCelciusOrFarenheit(){
    AlertDialog.Builder cof = new AlertDialog.Builder(this);
    cof.setTitle("Select Temperature Conversion");
    String[] types = {"To Celcius", "To Farenheit"};
    cof.setItems(types, new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int which) {
            dialog.dismiss();
            switch(which){
            case 0:
                createTempDialog(true).show();
                break;
            case 1:
                createTempDialog(false).show();
                break;
            }
        }
    });
    return cof.show();
    }
    public AlertDialog createTempDialog(final boolean cf){
       final EditText et = new EditText(this);
       et.setInputType(InputType.TYPE_CLASS_NUMBER|InputType.TYPE_NUMBER_FLAG_DECIMAL);
       final Formatter f = new Formatter();
       return new AlertDialog.Builder(this).setView(et).setTitle(cf?"Enter Farenheit temperature":"Enter Celcius temperature").setPositiveButton("OK", new DialogInterface.OnClickListener() {
           public void onClick(DialogInterface dialogInterface, int i) {
               double answer = 0;
               if (cf) {
                   answer = (Double.parseDouble(et.getText().length() > 1 ? et.getText().toString() : "0") - 32) * 5 / 9;
               } else {
                   answer = Double.parseDouble(et.getText().length() > 1 ? et.getText().toString() : "0")*9/5 + 32;
               }
               new AlertDialog.Builder(TempTest.this).setMessage(f.format("%.2f", answer).toString()).setTitle(cf?"Celcius":"Farenheit")
                       .setPositiveButton("OK", new DialogInterface.OnClickListener() {
                           public void onClick(DialogInterface dialogInterface, int i) {
                               dialogInterface.dismiss();
                           }
                       })
                       .create().show();
           }
       }).create();
    }

}