我是相當新的Android和我寫這將解決物理問題的應用程序。數學進展順利得益於這些論壇一些幫助,但是當我試圖從它與新活動的onCreate方法一個NullPointerException出現列表中開始我的活動。這似乎並沒有太大的意義,但因爲所有這就是有一個提交按鈕,從某些觀點的EditText執行數學。這是我的代碼。的NullPointerException在Android的程序中的onCreate()
package android.physicsengine;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import java.lang.Math;
public class ProjectileMotion extends Activity {
private EditText acceleration;
private EditText finalVelocity;
private EditText initialVelocity;
private EditText time;
private EditText deltay;
private EditText velocity;
private EditText deltax;
private Button submitButton;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.projectile_motion_layout);
submitButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
acceleration = (EditText)findViewById(R.id.acceleration);
double a = Doublify(acceleration);
finalVelocity = (EditText)findViewById(R.id.finalVelocity);
double vf = Doublify(finalVelocity);
initialVelocity = (EditText)findViewById(R.id.intitialVelocity);
double vi = Doublify(initialVelocity);
time = (EditText)findViewById(R.id.time);
double t = Doublify(time);
deltay = (EditText)findViewById(R.id.deltay);
double y = Doublify(deltay);
velocity = (EditText)findViewById(R.id.velocity);
double vx = Doublify(velocity);
deltax = (EditText)findViewById(R.id.deltax);
double x = Doublify(deltax);
//Y Axis
if(time.getText()==null && deltay.getText()==null){
time.setText(Double.toString((vf-vi)/a));
deltay.setText(Double.toString(((vf-vi)/a)+(a*Math.pow(((vf-vi)/a),2))));
}
if(acceleration.getText()==null && deltay.getText()==null){
acceleration.setText(Double.toString((vf-vi)/t));
deltay.setText(Double.toString((vi*t+.5*((vf-vi)/t))*Math.pow(t,2)));
}
if(acceleration.getText()==null && time.getText()==null){
acceleration.setText(Double.toString(((Math.pow(vf,2)-Math.pow(vi,2)))/2*y));
time.setText(Double.toString(2*y*(vf-vi)/(Math.pow(vf,2)-vi)));
}
if(initialVelocity.getText()==null && deltay.getText()==null){
initialVelocity.setText(Double.toString(vf-a*t));
deltay.setText(Double.toString((vf-a*t)*t+.5*a*Math.pow(t,2)));
}
if(initialVelocity.getText()==null && time.getText()==null){
initialVelocity.setText(Double.toString(Math.sqrt(Math.pow(vf,2)-2*a*y)));
time.setText(Double.toString((vf-Math.sqrt(Math.pow(vf,2)-2*a*y))/2));
}
if(initialVelocity.getText()==null && acceleration.getText()==null){
initialVelocity.setText(Double.toString(vf-2*(vf-y/t)));
acceleration.setText(Double.toString((2/t)*(vf-y/t)));
}
if(finalVelocity.getText()==null && deltay.getText()==null){
finalVelocity.setText(Double.toString(vi+a*t));
deltay.setText(Double.toString(vi*t+.5*a*Math.pow(t,2)));
}
if(finalVelocity.getText()==null && time.getText()==null){
finalVelocity.setText(Double.toString(Math.sqrt(Math.pow(vi,2)+2*a*y)));
time.setText(Double.toString(((Math.sqrt(Math.pow(vi,2)+2*a*y)-vi))/a));
}
if(finalVelocity.getText()==null && acceleration.getText()==null){
acceleration.setText(Double.toString(2*(y-vi*t)/Math.pow(t,2)));
finalVelocity.setText(Double.toString(vi+(2*(y-vi*t)/t)));
}
if(finalVelocity.getText()==null && initialVelocity.getText()==null){
initialVelocity.setText(Double.toString((y-.5*a*Math.pow(t,2))/t));
finalVelocity.setText(Double.toString((y-.5*a*Math.pow(t,2))/t)+a*t);
}
}
});
}
private double Doublify(EditText editText){
if(editText.getText()!= null){
return Double.parseDouble(editText.getText().toString());
}
return 0;
}
}
和XML
<?xml version="1.0" encoding="utf-8"?>
<TableLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical">
<TableRow>
<TextView android:text="Projectile Motion Engine"
android:textSize="25dip"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_span="4"
android:layout_gravity="center" />
</TableRow>
<TableRow>
<TextView android:text="X axis"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_span="2"
android:textStyle="bold"/>
<TextView android:text="Y axis"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_span="2"
android:textStyle="bold"/>
</TableRow>
<TableRow>
<TextView android:text="accel(m/s^2)="
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
<EditText android:id="@+id/acceleration"
android:text="9.8"
android:inputType="numberDecimal"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
<TextView android:text="deltax(m)="
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
<EditText android:id="@+id/deltax"
android:inputType="numberDecimal"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
</TableRow>
<TableRow>
<TextView android:text="init v(m/s)="
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
<EditText android:id="@+id/intitialVelocity"
android:inputType="numberDecimal"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
<TextView android:text="v ="
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
<EditText android:id="@+id/velocity"
android:inputType="numberDecimal"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
</TableRow>
<TableRow>
<TextView android:text="final v(m/s)="
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
<EditText android:id="@+id/finalVelocity"
android:inputType="numberDecimal"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
<TextView android:text="time(s)="
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
<EditText android:id="@+id/time"
android:inputType="numberDecimal"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
</TableRow>
<TableRow>
<TextView android:text="deltay(m)="
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
<EditText android:id="@+id/deltay"
android:inputType="numberDecimal"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
<Button android:id="@+id/submitButton"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_span="2"
android:text="Launch" />
</TableRow>
</TableLayout>
以供將來參考,如果你有一大塊代碼,您可以通過突出顯示的代碼塊擊中了`{}`按鈕對其進行格式化。使用反引號僅適用於內聯代碼IIRC。 – eldarerathis 2011-01-20 19:49:35
發佈StackTrace並確定它拋出哪一行。 – 2011-01-20 19:53:15