我花了一点时间浏览了一些 Google 的 android 教程，并决定拼凑出我自己的简单计算器应用程序。我对 JAVA 了解很多，并且在几个 SDK 之前搞砸了一点 Android。我认为代码很好，但我就是无法让这个 SCSS 运行。我一直试图根据我的 LogCat 内容找到答案，但没有运气。首先，这是我的 MainActivity.java:
package com.AppliedArgonautics.calculator;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.widget.EditText;
import android.widget.TextView;
public class MainActivity extends Activity {
EditText editText1 = (EditText)findViewById(R.id.editText1);
EditText editText2 = (EditText)findViewById(R.id.editText2);
TextView textView1 = (TextView)findViewById(R.id.textView1);
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
public void Add(){
float num1 = Float.parseFloat(editText1.getText().toString());
float num2 = Float.parseFloat(editText2.getText().toString());
float result = num1 + num2;
textView1.setText(Float.toString(result));
}
public void Subtract(){
float num1 = Float.parseFloat(editText1.getText().toString());
float num2 = Float.parseFloat(editText2.getText().toString());
float result = num1 - num2;
textView1.setText(Float.toString(result));
}
public void Multiply(){
float num1 = Float.parseFloat(editText1.getText().toString());
float num2 = Float.parseFloat(editText2.getText().toString());
float result = num1 * num2;
textView1.setText(Float.toString(result));
}
public void Divide(){
float num1 = Float.parseFloat(editText1.getText().toString());
float num2 = Float.parseFloat(editText2.getText().toString());
float result = num1 / num2;
textView1.setText(Float.toString(result));
}
public void Clear(){
editText1.setText("");
editText2.setText("");
textView1.setText("");
}
}
我的 list 文件:
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.AppliedArgonautics.calculator"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="15" />
<application
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/title_activity_main" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
然后，activity_main.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<Button
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_centerVertical="true"
android:layout_marginLeft="32dp"
android:onClick="Add"
android:text="Add" />
<Button
android:id="@+id/button3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/button1"
android:layout_below="@+id/button1"
android:layout_marginTop="45dp"
android:onClick="Multiply"
android:text="Multiply" />
<Button
android:id="@+id/button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_above="@+id/button3"
android:layout_alignParentRight="true"
android:layout_marginRight="28dp"
android:onClick="Subtract"
android:text="Subtract" />
<Button
android:id="@+id/button4"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="@+id/button3"
android:layout_alignBottom="@+id/button3"
android:layout_alignLeft="@+id/button2"
android:onClick="Divide"
android:text="Divide" />
<Button
android:id="@+id/button5"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/button1"
android:layout_centerHorizontal="true"
android:onClick="Clear"
android:text="Clear" />
<EditText
android:id="@+id/editText1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_alignRight="@+id/button1"
android:layout_marginTop="37dp"
android:ems="10"
android:inputType="phone" >
<requestFocus />
</EditText>
<EditText
android:id="@+id/editText2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBottom="@+id/editText1"
android:layout_alignLeft="@+id/button2"
android:layout_alignParentRight="true"
android:layout_alignTop="@+id/editText1"
android:ems="10"
android:inputType="phone" />
<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/button5"
android:layout_below="@+id/editText1"
android:layout_marginTop="56dp"
android:text="TextView" />
</RelativeLayout>
这是我尝试运行 LogCat 时显示的内容:
/Trace ( 3186): error opening trace file: No such file or directory (2)
D/AndroidRuntime( 3186): Shutting down VM
W/dalvikvm( 3186): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
E/AndroidRuntime( 3186): FATAL EXCEPTION: main
E/AndroidRuntime( 3186): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.AppliedArgonautics.calculator/com.AppliedArgonautics.calculator.MainActivi ty}: java.lang.NullPointerException
E/AndroidRuntime( 3186): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1983)
E/AndroidRuntime( 3186): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
E/AndroidRuntime( 3186): at android.app.ActivityThread.access$600(ActivityThread.java:130)
E/AndroidRuntime( 3186): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
E/AndroidRuntime( 3186): at android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime( 3186): at android.os.Looper.loop(Looper.java:137)
E/AndroidRuntime( 3186): at android.app.ActivityThread.main(ActivityThread.java:4745)
E/AndroidRuntime( 3186): at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime( 3186): at java.lang.reflect.Method.invoke(Method.java:511)
E/AndroidRuntime( 3186): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
E/AndroidRuntime( 3186): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
E/AndroidRuntime( 3186): at dalvik.system.NativeStart.main(Native Method)
E/AndroidRuntime( 3186): Caused by: java.lang.NullPointerException
E/AndroidRuntime( 3186): at android.app.Activity.findViewById(Activity.java:1825)
E/AndroidRuntime( 3186): at com.AppliedArgonautics.calculator.MainActivity.<init>(MainActivity.java:10)
E/AndroidRuntime( 3186): at java.lang.Class.newInstanceImpl(Native Method)
E/AndroidRuntime( 3186): at java.lang.Class.newInstance(Class.java:1319)
E/AndroidRuntime( 3186): at android.app.Instrumentation.newActivity(Instrumentation.java:1053)
E/AndroidRuntime( 3186): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1974)
E/AndroidRuntime( 3186): ... 11 more
W/ActivityManager( 160): Force finishing activity com.AppliedArgonautics.calculator/.MainActivity
如果有人能看到这个，我将不胜感激。我认为学习 android 会很酷，但我对无法启动像这样的简单程序感到非常沮丧。谢谢。
最佳答案
您的代码中可能存在很多问题，但首先要让您入门:
创建EditText 和TextView 作为实例变量。在 onCreate 中为这些变量分配 View 。
public class MainActivity extends Activity {
EditText editText1;
EditText editText2;
TextView textView1;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
editText1 = (EditText)findViewById(R.id.editText1);
editText2 = (EditText)findViewById(R.id.editText2);
textView1 = (TextView)findViewById(R.id.textView1);
}
.........
}
关于java - 无法运行简单的安卓计算器应用程序，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/13080429/