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
答案 0 :(得分：5)
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;
}
答案 1 :(得分：0)
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();
}
}