MainActivity.java：这是主要的活动类。运行此命令时，预期输出是相应xml中描述的表。但是在给我第一页本身之前，应用程序崩溃了。log-cat中的错误显示为空指针异常。
package com.codeitsuisse.team71.expensetracker;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.TextView;
public class MainActivity extends Activity {
TextView t1= (TextView) findViewById(R.id.textView1);
TextView t3= (TextView) findViewById(R.id.textView3);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
@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;
}
public void goto_bgt(View v){
Intent i= new Intent (MainActivity.this, Budget.class);
//startActivityForResult(i, 1);
}
protected void onActivityResult(int requestCode, int resultCode, Intent data)
{
super.onActivityResult(requestCode, resultCode, data);
// check if the request code is same as what is passed here it is 2
if(requestCode==1)
{
double k=data.getDoubleExtra("budget",0);
double d= data.getDoubleExtra("goal",0);
t1.setText(k+"");
t3.setText(d+"");
}
}
}
activity_main.xml：
<LinearLayout
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:weightSum="1"
android:id="@+id/linearLayout">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="WELCOME USER!"
android:id="@+id/textView"
android:layout_gravity="center_horizontal" />
<TableLayout android:id="@+id/tabla_cuerpo"
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:layout_marginTop="200dp"
android:background="#FF0000">
<TableRow android:id="@+id/tableRow1"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TextView android:textColor="#000"
android:textStyle="bold"
android:gravity="center_horizontal"
android:background="#f00" android:layout_margin="1dip"
android:id="@+id/textViewb" android:layout_weight="0.3"
android:layout_width="100dp" android:layout_height="50dp"
android:textAppearance="?android:attr/textAppearanceMedium"
android:text="BUDGET"/>
<TextView android:textColor="#000"
android:textStyle="bold"
android:gravity="center_horizontal"
android:background="#f00" android:layout_margin="1dip"
android:id="@+id/textViewe" android:layout_weight="0.3"
android:layout_width="100dp" android:layout_height="50dp"
android:textAppearance="?android:attr/textAppearanceMedium"
android:text="EXPENSES"/>
<TextView android:textColor="#000"
android:textStyle="bold"
android:gravity="center_horizontal"
android:background="#f00" android:layout_margin="1dip"
android:id="@+id/textViewg" android:layout_weight="0.3"
android:layout_width="100dp" android:layout_height="50dp"
android:textAppearance="?android:attr/textAppearanceMedium"
android:text="SAVINGS GOAL"/>
</TableRow>
<TableRow android:id="@+id/tableRow1"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TextView android:background="#000000"
android:textColor="#FFFFFF"
android:layout_margin="1dip"
android:id="@+id/textView1"
android:layout_weight="0.3"
android:layout_width="wrap_content"
android:layout_height="40dp"
android:textAppearance="?android:attr/textAppearanceMedium"
android:text="Celda1"/>
<TextView android:background="#000000"
android:textColor="#FFFFFF"
android:layout_margin="1dip"
android:id="@+id/textView2"
android:layout_weight="0.3"
android:layout_width="wrap_content"
android:layout_height="40dp"
android:textAppearance="?android:attr/textAppearanceMedium"
android:text="Celda2"/>
<TextView android:background="#000000"
android:layout_margin="1dip"
android:textColor="#FFFFFF"
android:id="@+id/textView3"
android:layout_weight="0.3"
android:layout_width="wrap_content"
android:layout_height="40dp"
android:textAppearance="?android:attr/textAppearanceMedium"
android:text="Celda3"/>
</TableRow>
</TableLayout>
</LinearLayout>
<LinearLayout
android:id="@+id/linearLayout2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:layout_below="@+id/linearLayout"
android:layout_marginTop="27dp"
android:orientation="horizontal" >
<Button
android:id="@+id/button"
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_below="@+id/linearLayout2"
android:text="update budget"
android:onClick="goto_bgt"
/>
<Button
android:id="@+id/button2"
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="update exp" />
</LinearLayout>
我的日志是
> (MainActivity.java:11) 09-12 12:08:25.358: E/AndroidRuntime(1504): at
> java.lang.reflect.Constructor.newInstance(Native Method) 09-12
> 12:08:25.358: E/AndroidRuntime(1504): at
> java.lang.Class.newInstance(Class.java:1572) 09-12 12:08:25.358:
> E/AndroidRuntime(1504): at
> android.app.Instrumentation.newActivity(Instrumentation.java:1088)
> 09-12 12:08:25.358: E/AndroidRuntime(1504): at
> android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2215)
> 09-12 12:08:25.358: E/AndroidRuntime(1504): ... 10 more -->
在之后使用 setContentView(R.layout.activity_main)
TextView t1= (TextView) findViewById(R.id.textView1);
TextView t3= (TextView) findViewById(R.id.textView3);
和
TextView t1,t3;
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
t1= (TextView) findViewById(R.id.textView1);
t3= (TextView) findViewById(R.id.textView3);
......
}
}
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