我试图为Android制作温度转换器应用程序。 我想使用2个微调器（＆＃34; From＆＃34;和＃34; To＆＃34;）。 有3个项目，Celsius，Kelvin和Fahrenheit。 我还添加了一个文本字段，用户将在其中放入一个数字。 在底部有一个按钮＆＃34;转换＆＃34;和一个结果的textview。 现在我需要的是，当＆＃34;转换＆＃34;按下按钮textview由结果替换，但取决于2个微调器中的选定项目。 例如，如果选定的项目是从摄氏度到华氏度，它应该计算如下结果： 9/5 *（用户写的数字）+32 所以我的问题是我该怎么做，我想我应该使用＆＃34;如果＆＃34;但我不确定如何，因为物品没有被任何东西定义：
<?xml version="1.0" encoding="utf-8"?>
<resources>
<string-array name="From">
<item>Celsius</item>
<item>Kelvin</item>
<item>Fahrenheit</item>
</string-array>
</resources>
顺便说一下，这是我为旋转器显示的值中的xml文件。 这是我的MainActivity：
package com.usc.uscconverter;
import android.support.v7.app.ActionBarActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.TextView;
public class MainActivity extends ActionBarActivity {
Spinner sp, sp2;
TextView textFrom, textTo, textDegree, textResult;
EditText editText1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
sp=(Spinner) findViewById(R.id.spinner1);
ArrayAdapter<CharSequence> ar= ArrayAdapter.createFromResource(this, R.array.From, android.R.layout.simple_list_item_1);
ar.setDropDownViewResource(android.R.layout.simple_dropdown_item_1line);
sp.setAdapter(ar);
sp2=(Spinner) findViewById(R.id.spinner2);
ArrayAdapter<CharSequence> ar2= ArrayAdapter.createFromResource(this, R.array.To, android.R.layout.simple_list_item_1);
ar2.setDropDownViewResource(android.R.layout.simple_dropdown_item_1line);
sp2.setAdapter(ar2);
Button buttonConvert = (Button) findViewById(R.id.buttonConvert);
buttonConvert.setOnClickListener(new OnClickListener(){
public void onClick(View v){
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
修改 我编辑了我的主要活动并添加了这个：
Button buttonConvert = (Button) findViewById(R.id.buttonConvert);
buttonConvert.setOnClickListener(new OnClickListener(){
public void onClick(View v){
if (sp.getSelectedItem().toString().equals("Celsius") && sp2.getSelectedItem().toString().equals("Fahrenheit")){
editText1 = (EditText)findViewById(R.id.editText1);
num = editText1.getText().toString();
int d = 9/5;
int n = Integer.parseInt(num);
int r = d * n + 32;
textResult.setText(String.valueOf(r));
}
}
});
虽然没有错误，但是当我启动应用程序时它会崩溃，而在logcat中它会像这样说：
11-29 18:42:24.890: D/dalvikvm(846): Not late-enabling CheckJNI (already on)
11-29 18:42:36.830: I/Choreographer(846): Skipped 165 frames! The application may be doing too much work on its main thread.
11-29 18:42:37.840: D/gralloc_goldfish(846): Emulator without GPU emulation detected.
11-29 18:42:41.740: D/dalvikvm(846): GC_FOR_ALLOC freed 113K, 6% free 2971K/3156K, paused 39ms, total 46ms
11-29 18:42:41.980: I/Choreographer(846): Skipped 75 frames! The application may be doing too much work on its main thread.
11-29 18:42:43.240: I/Choreographer(846): Skipped 118 frames! The application may be doing too much work on its main thread.
11-29 18:42:44.190: I/Choreographer(846): Skipped 102 frames! The application may be doing too much work on its main thread.
11-29 18:42:45.330: I/Choreographer(846): Skipped 79 frames! The application may be doing too much work on its main thread.
11-29 18:42:45.630: I/Choreographer(846): Skipped 57 frames! The application may be doing too much work on its main thread.
11-29 18:42:50.050: D/AndroidRuntime(846): Shutting down VM
11-29 18:42:50.050: W/dalvikvm(846): threadid=1: thread exiting with uncaught exception (group=0xb2a42ba8)
11-29 18:42:50.060: E/AndroidRuntime(846): FATAL EXCEPTION: main
11-29 18:42:50.060: E/AndroidRuntime(846): Process: com.usc.uscconverter, PID: 846
11-29 18:42:50.060: E/AndroidRuntime(846): java.lang.NullPointerException
11-29 18:42:50.060: E/AndroidRuntime(846): at com.usc.uscconverter.MainActivity$1.onClick(MainActivity.java:49)
11-29 18:42:50.060: E/AndroidRuntime(846): at android.view.View.performClick(View.java:4438)
11-29 18:42:50.060: E/AndroidRuntime(846): at android.view.View$PerformClick.run(View.java:18422)
11-29 18:42:50.060: E/AndroidRuntime(846): at android.os.Handler.handleCallback(Handler.java:733)
11-29 18:42:50.060: E/AndroidRuntime(846): at android.os.Handler.dispatchMessage(Handler.java:95)
11-29 18:42:50.060: E/AndroidRuntime(846): at android.os.Looper.loop(Looper.java:136)
11-29 18:42:50.060: E/AndroidRuntime(846): at android.app.ActivityThread.main(ActivityThread.java:5017)
11-29 18:42:50.060: E/AndroidRuntime(846): at java.lang.reflect.Method.invokeNative(Native Method)
11-29 18:42:50.060: E/AndroidRuntime(846): at java.lang.reflect.Method.invoke(Method.java:515)
11-29 18:42:50.060: E/AndroidRuntime(846): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
11-29 18:42:50.060: E/AndroidRuntime(846): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
11-29 18:42:50.060: E/AndroidRuntime(846): at dalvik.system.NativeStart.main(Native Method)
11-29 18:42:54.150: I/Process(846): Sending signal. PID: 846 SIG: 9
答案 0 :(得分：0)
将此添加到您的代码中：
textResult = (TextView)findViewById(R.id.textResult);