我有一个按钮id = button1，当点击它时会运行onEnterClick();功能但是每当我点击它时我的应用程序崩溃并说unexpectedly quit。我将在下面提供java文件和xml，非常感谢任何帮助。
package tip.calculator;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.widget.EditText;
import android.widget.TextView;
import android.view.View;
public class MainActivity extends Activity {
final EditText myEditField = (EditText) findViewById(R.id.percentText);
final EditText myEditField2 = (EditText) findViewById(R.id.billText);
@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 onEnterClick(View view){ //This Function Runs When The Button is clicked
TextView textView;
textView =
(TextView) findViewById(R.id.textView1);
final EditText myEditField = (EditText) findViewById(R.id.percentText);
final EditText myEditField2 = (EditText) findViewById(R.id.billText);
int percentage;
int percentageInp;
int billAmount;
int output;
String output1;
percentageInp = Integer.parseInt(myEditField.getText().toString());
billAmount = Integer.parseInt(myEditField2.getText().toString());
percentage = percentageInp /100;
output = (billAmount * percentage);
output1 = Integer.toString(output);
textView.setText(output1);
}
}
<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"
android:onClick="onEnterClick" >
<EditText
android:id="@+id/billText"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:ems="10"
android:hint="Bill Amount"
android:inputType="numberDecimal|textAutoComplete" />
<EditText
android:id="@+id/percentText"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/billText"
android:layout_below="@+id/billText"
android:ems="10"
android:hint="Percent"
android:inputType="number" >
<requestFocus />
</EditText>
<Button
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/percentText"
android:layout_centerHorizontal="true"
android:onClick="onEnterClick"
android:text="Calculate" />
<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="287dp"
android:text="Solution Will Appear Here:"
android:textAppearance="?android:attr/textAppearanceLarge" />
</RelativeLayout>
Log Cat：
07-24 03:12:26.563: D/AndroidRuntime(412): Shutting down VM
07-24 03:12:26.563: W/dalvikvm(412): threadid=1: thread exiting with uncaught exception (group=0x40014760)
07-24 03:12:26.763: E/AndroidRuntime(412): FATAL EXCEPTION: main
07-24 03:12:26.763: E/AndroidRuntime(412): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{tip.calculator/tip.calculator.MainActivity}: java.lang.NullPointerException
07-24 03:12:26.763: E/AndroidRuntime(412): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1739)
07-24 03:12:26.763: E/AndroidRuntime(412): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1831)
07-24 03:12:26.763: E/AndroidRuntime(412): at android.app.ActivityThread.access$500(ActivityThread.java:122)
07-24 03:12:26.763: E/AndroidRuntime(412): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1024)
07-24 03:12:26.763: E/AndroidRuntime(412): at android.os.Handler.dispatchMessage(Handler.java:99)
07-24 03:12:26.763: E/AndroidRuntime(412): at android.os.Looper.loop(Looper.java:132)
07-24 03:12:26.763: E/AndroidRuntime(412): at android.app.ActivityThread.main(ActivityThread.java:4123)
07-24 03:12:26.763: E/AndroidRuntime(412): at java.lang.reflect.Method.invokeNative(Native Method)
07-24 03:12:26.763: E/AndroidRuntime(412): at java.lang.reflect.Method.invoke(Method.java:491)
07-24 03:12:26.763: E/AndroidRuntime(412): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
07-24 03:12:26.763: E/AndroidRuntime(412): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
07-24 03:12:26.763: E/AndroidRuntime(412): at dalvik.system.NativeStart.main(Native Method)
07-24 03:12:26.763: E/AndroidRuntime(412): Caused by: java.lang.NullPointerException
07-24 03:12:26.763: E/AndroidRuntime(412): at android.app.Activity.findViewById(Activity.java:1745)
07-24 03:12:26.763: E/AndroidRuntime(412): at tip.calculator.MainActivity.<init>(MainActivity.java:12)
07-24 03:12:26.763: E/AndroidRuntime(412): at java.lang.Class.newInstanceImpl(Native Method)
07-24 03:12:26.763: E/AndroidRuntime(412): at java.lang.Class.newInstance(Class.java:1301)
07-24 03:12:26.763: E/AndroidRuntime(412): at android.app.Instrumentation.newActivity(Instrumentation.java:1022)
07-24 03:12:26.763: E/AndroidRuntime(412): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1730)
07-24 03:12:26.763: E/AndroidRuntime(412): ... 11 more
07-24 03:12:34.871: I/Process(412): Sending signal. PID: 412 SIG: 9
07-24 03:15:54.102: D/AndroidRuntime(453): Shutting down VM
07-24 03:15:54.216: W/dalvikvm(453): threadid=1: thread exiting with uncaught exception (group=0x40014760)
07-24 03:15:54.381: E/AndroidRuntime(453): FATAL EXCEPTION: main
07-24 03:15:54.381: E/AndroidRuntime(453): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{tip.calculator/tip.calculator.MainActivity}: java.lang.NullPointerException
07-24 03:15:54.381: E/AndroidRuntime(453): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1739)
07-24 03:15:54.381: E/AndroidRuntime(453): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1831)
07-24 03:15:54.381: E/AndroidRuntime(453): at android.app.ActivityThread.access$500(ActivityThread.java:122)
07-24 03:15:54.381: E/AndroidRuntime(453): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1024)
07-24 03:15:54.381: E/AndroidRuntime(453): at android.os.Handler.dispatchMessage(Handler.java:99)
07-24 03:15:54.381: E/AndroidRuntime(453): at android.os.Looper.loop(Looper.java:132)
07-24 03:15:54.381: E/AndroidRuntime(453): at android.app.ActivityThread.main(ActivityThread.java:4123)
07-24 03:15:54.381: E/AndroidRuntime(453): at java.lang.reflect.Method.invokeNative(Native Method)
07-24 03:15:54.381: E/AndroidRuntime(453): at java.lang.reflect.Method.invoke(Method.java:491)
07-24 03:15:54.381: E/AndroidRuntime(453): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
07-24 03:15:54.381: E/AndroidRuntime(453): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
07-24 03:15:54.381: E/AndroidRuntime(453): at dalvik.system.NativeStart.main(Native Method)
07-24 03:15:54.381: E/AndroidRuntime(453): Caused by: java.lang.NullPointerException
07-24 03:15:54.381: E/AndroidRuntime(453): at android.app.Activity.findViewById(Activity.java:1745)
07-24 03:15:54.381: E/AndroidRuntime(453): at tip.calculator.MainActivity.<init>(MainActivity.java:12)
07-24 03:15:54.381: E/AndroidRuntime(453): at java.lang.Class.newInstanceImpl(Native Method)
07-24 03:15:54.381: E/AndroidRuntime(453): at java.lang.Class.newInstance(Class.java:1301)
07-24 03:15:54.381: E/AndroidRuntime(453): at android.app.Instrumentation.newActivity(Instrumentation.java:1022)
07-24 03:15:54.381: E/AndroidRuntime(453): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1730)
07-24 03:15:54.381: E/AndroidRuntime(453): ... 11 more
答案 0 :(得分：0)
在调用setContentView(R.layout.activity_main);部分之前，请不要初始化UI元素。
将您的代码更改为
public class MainActivity extends Activity
{
private EditText myEditField;
private EditText myEditField2;
private Button enter;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
myEditField = (EditText) findViewById(R.id.percentText);
myEditField2 = (EditText) findViewById(R.id.billText);
enter = (Button)findViewById(R.id.button1);
enter.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
TextView textView;
textView = (TextView) findViewById(R.id.textView1);
final EditText myEditField = (EditText) findViewById(R.id.percentText);
final EditText myEditField2 = (EditText) findViewById(R.id.billText);
float percentage;//=======> declate as float
int percentageInp;
int billAmount;
int output;
String output1;
percentageInp = Integer.parseInt(myEditField.getText().toString());
billAmount = Integer.parseInt(myEditField2.getText().toString());
System.out.println(percentageInp+" "+billAmount);
percentage = ((float)percentageInp /100);//=====>check here
output = (int)(billAmount * percentage);
output1 = Integer.toString(output);
textView.setText(output1);
}
});
}
}