我创建了一个基本转换应用，可以将用户输入转换为km-knots，反之亦然。目前，它将结果显示在用户最初键入其图形的位置。我想知道如何在新活动中显示结果？目前我只是设法让它出现，正如我所说，在用户最初键入其数字的位置和第二个活动弹出后的第二个位置。我在这里错过了什么？请看一下我的代码，谢谢：
MainActivity.java
package winfield.joe.wind.v1;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.View;
import android.widget.EditText;
import android.widget.RadioButton;
import android.widget.Toast;
public class MainActivity extends Activity {
// public var
private EditText text;
// default func
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Toast.makeText(this, "onCreate!", Toast.LENGTH_LONG).show();
setContentView(R.layout.activity_main);
// findViewById = Finds a view that was identified by the id attribute
// from the XML that was processed in onCreate(Bundle).
// (EditText) = typecast
text = (EditText) findViewById(R.id.userInput);
}
//Will be executed by clicking on the calculate button because we assigned "calc" to the "onClick" Property
public void calc(View view) {
RadioButton toKilometers = (RadioButton) findViewById(R.id.toKilometers);
RadioButton toKnots = (RadioButton) findViewById(R.id.toKnots);
if (text.getText().length() == 0) {
// if the text field is empty show the message "enter a valid number" via toast message
Toast.makeText(this, "enter a valid number", Toast.LENGTH_LONG).show();
} else {
int result = R.string.userInput;
Intent i = new Intent(MainActivity.this, SecondActivity.class);
putExtra("userInput", result);
startActivity(i);
// parse input Value from Text Field
double inputValue = Double.parseDouble(text.getText().toString());
// convert to...
if (toKilometers.isChecked()) {
text.setText(String.valueOf(convertToKM(inputValue)));
// uncheck "to km" Button
toKilometers.setChecked(false);
// check "to knots" Button
toKnots.setChecked(true);
} else { /* if toKnots button isChecked() */
text.setText(String.valueOf(convertToKnots(inputValue)));
// uncheck "to knots" Button
toKnots.setChecked(false);
// check "to km" Button
toKilometers.setChecked(true);
}
}
}
private void putExtra(String string, int result) {
// TODO Auto-generated method stub
}
private double convertToKM(double inputValue) {
// convert knots to km
return (inputValue * 1.8);
}
private double convertToKnots(double inputValue) {
// convert km to knots
return (inputValue * 0.539956803);
}
}
SecondActivity.java
package winfield.joe.wind.v1;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
public class SecondActivity extends Activity {
Bundle extras = getIntent().getExtras();
int result = extras.getInt("results");
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second);
}
//onClick GoBack method assigned to the Go Back? button which returns the user to main activity from the second activity
public void GoBack(View view) {
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("Are you sure?");
// set dialog message
builder .setCancelable(false)
.setPositiveButton("Convert Again",new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,int id) {
//You return to Main Activity
Intent intent = new Intent(SecondActivity.this, MainActivity.class);
startActivity(intent);
}
})
.setNeutralButton("Back to Home",new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,int id) {
//You return to the home page
Intent intent = new Intent(Intent.ACTION_MAIN);
intent.addCategory(Intent.CATEGORY_HOME);
startActivity(intent);
}
})
.setNegativeButton("View Results",new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,int id) {
// if this button is clicked, just close the dialog box and do nothing
dialog.cancel();
}
});
AlertDialog alert = builder.create();
alert.show();
}
}
activity_main.xml中
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/LinearLayout1"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_alignParentBottom="true"
android:layout_alignParentEnd="true"
android:background="@color/bgColor"
android:orientation="vertical">
<!--TITLE-->
<TextView
android:id="@+id/titleMain"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginTop="22dp"
android:gravity="center"
android:text="@string/titleMain"
android:textColor="@color/textColor"
android:textColorHint="@color/textColor"
android:textColorLink="#ffffff"
android:textSize="30sp" />
<!--USER-INPUT-->
<EditText
android:id="@+id/userInput"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginLeft="20dp"
android:layout_marginRight="20dp"
android:ems="10"
android:hint="@+string/userInput"
android:inputType="numberDecimal"
android:paddingEnd="40dp"
android:paddingStart="20dp"
android:paddingTop="30dp" >
<requestFocus />
</EditText>
<!--TWO RADIO BUTTONS-->
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingLeft="10dp"
android:paddingRight="10dp">
<!--toKNOTS-->
<RadioButton
android:id="@+id/toKnots"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginStart="10dp"
android:layout_marginTop="10dp"
android:layout_weight="0.04"
android:checked="true"
android:text="@string/toKnots" />
<!--toKM-->
<RadioButton
android:id="@+id/toKilometers"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginEnd="20dp"
android:layout_marginTop="10dp"
android:text="@string/toKilometers" />
</LinearLayout>
<!--CALCULATE-->
<Button
android:id="@+id/valueCalc"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginEnd="10dp"
android:layout_marginStart="10dp"
android:layout_marginTop="30dp"
android:onClick="calc"
android:text="@string/valueCalc" />
</LinearLayout>
activity_second.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/LinearLayout1"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_alignParentBottom="true"
android:layout_alignParentEnd="true"
android:background="@color/bgColor"
android:orientation="vertical"
tools:context="${relativePackage}.${activityClass}" >
<!-- TITLE -->
<TextView
android:id="@+id/titleResults"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginTop="24dp"
android:gravity="center"
android:text="@string/titleResults"
android:textColor="@color/textColor"
android:textColorHint="@color/textColor"
android:textColorLink="#ffffff"
android:textSize="25sp" />
<EditText
android:id="@+id/results"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_margin="20dp"
android:layout_marginTop="30dp"
android:ems="10"
android:hint="@string/results"
android:inputType="numberDecimal"
android:textColorHint="@color/textColor" >
<requestFocus />
</EditText>
<Button
android:id="@+id/GoBack"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginTop="40dp"
android:text="@string/GoBack"
android:onClick="GoBack" />
</LinearLayout>
logcat的
03-09 12:27:35.692: E/AndroidRuntime(2911): java.lang.RuntimeException: Unable to start activity ComponentInfo{winfield.joe.wind.v1/winfield.joe.wind.v1.SecondActivity}: java.lang.NullPointerException
03-09 12:27:35.692: E/AndroidRuntime(2911): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
03-09 12:27:45.262: E/AndroidRuntime(2934): java.lang.RuntimeException: Unable to start activity ComponentInfo{winfield.joe.wind.v1/winfield.joe.wind.v1.SecondActivity}: java.lang.NullPointerException
03-09 12:27:45.262: E/AndroidRuntime(2934): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
03-09 12:29:52.172: E/AndroidRuntime(2989): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{winfield.joe.wind.v1/winfield.joe.wind.v1.SecondActivity}: java.lang.NullPointerException
03-09 12:29:52.172: E/AndroidRuntime(2989): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
03-09 12:32:29.322: E/AndroidRuntime(3056): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{winfield.joe.wind.v1/winfield.joe.wind.v1.SecondActivity}: java.lang.NullPointerException
03-09 12:32:29.322: E/AndroidRuntime(3056): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
03-09 12:36:29.872: E/AndroidRuntime(3112): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{winfield.joe.wind.v1/winfield.joe.wind.v1.SecondActivity}: java.lang.NullPointerException
03-09 12:36:29.872: E/AndroidRuntime(3112): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
03-09 12:44:25.022: E/AndroidRuntime(3172): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{winfield.joe.wind.v1/winfield.joe.wind.v1.SecondActivity}: java.lang.NullPointerException
03-09 12:44:25.022: E/AndroidRuntime(3172): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
03-09 12:53:38.802: E/AndroidRuntime(3242): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{winfield.joe.wind.v1/winfield.joe.wind.v1.SecondActivity}: java.lang.NullPointerException
03-09 12:53:38.802: E/AndroidRuntime(3242): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
03-09 13:19:58.122: E/AndroidRuntime(3299): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{winfield.joe.wind.v1/winfield.joe.wind.v1.SecondActivity}: java.lang.NullPointerException
03-09 13:19:58.122: E/AndroidRuntime(3299): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
答案 0 :(得分：1)
如果您想将任何内容从一个活动传递到另一个活动，您可以通过有意使用putExtra来执行此操作，它会将数据从一个活动发送到另一个活动，而在另一个活动中通过使用{来获取该数据{1}}。
发送数据，
getExtras要接收其他活动中的数据，
String str = "value";
Intent launchResult = new Intent(MainActivity.this, SecondActivity.class);
putExtra("key", str);
startActivity(launchResult);
修改
在我的回答Bundle extras = getIntent().getExtras();
String str = extras.getStr("key");
中，任何唯一值必须在key和Sender Activity中保持一致。
您收到错误是因为您传递了字符串值，您必须传递键，并且接收者活动中的键也不匹配。
请参阅下面的更改，它应该有效
Receiver Activity
MainActivity.class int result = R.string.userInput;
Intent i = new Intent(MainActivity.this, SecondActivity.class);
putExtra("userInput", result);
startActivity(i);
SecondActivity.class答案 1 :(得分：1)
使用以下代码将值从一个Activity传递到另一个
Intent launchResult = new Intent(MainActivity.this, SecondActivity.class);
launchResult.putExtra("output",result);