我正在尝试获取a，b和c值作为来自编辑文本字符串的浮点数，但是在创建新类时它们似乎没有更新二次类。
Android代码。在第一部分中，“ savenum”是我期望a，b和c浮点数被更新的地方。稍后当我使用final Quadratic quad = new Quadratic（a，b，c）方法调用它们时，它们似乎没有更新。对话框中显示的值应显示在edittext框中输入的值是0.0。 ：
package com.bensherman.quadroid;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.AlertDialog.Builder;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
public class QuadraticdroidActivity extends Activity {
/** Called when the activity is first created. */
private EditText entA, entB, entC;
float a, b, c;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
SharedPreferences QuadPref = this.getSharedPreferences("QUADROID", MODE_PRIVATE);
final SharedPreferences.Editor QuadEdit = QuadPref.edit();
Button savenum = (Button) findViewById(R.id.btnSave);
savenum.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
entA = (EditText) findViewById(R.id.entA);
float a = Float.parseFloat(entA.getText().toString());
QuadEdit.putFloat("a", a).commit();
entB = (EditText) findViewById(R.id.entB);
float b = Float.parseFloat(entB.getText().toString());
QuadEdit.putFloat("b", b).commit();
entC = (EditText) findViewById(R.id.entC);
float c = Float.parseFloat(entC.getText().toString());
QuadEdit.putFloat("c", c).commit();
}
});
final Quadratic quad = new Quadratic(a, b, c);
final Builder showX = new AlertDialog.Builder(this);
Button getX = (Button) findViewById(R.id.getXb);
showX.setTitle("X Value");
getX.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
showX.setMessage("X: " + Math.round(quad.getXvalue()));
showX.show();
}
});
final Builder showY = new AlertDialog.Builder(this);
Button getY = (Button) findViewById(R.id.getYb);
showY.setTitle("Y Value");
getY.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
showY.setMessage("Y: " + Math.round(quad.getYvalue()));
showY.show();
}
});
final Builder showA = new AlertDialog.Builder(this);
Button getA = (Button) findViewById(R.id.getAb);
showA.setTitle("A Value");
getA.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
showA.setMessage("A: " + quad.getA());
showA.show();
}
});
final Builder showB = new AlertDialog.Builder(this);
Button getB = (Button) findViewById(R.id.getBb);
showB.setTitle("B Value");
getB.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
showB.setMessage("B: " + quad.getB());
showB.show();
}
});
final Builder showC = new AlertDialog.Builder(this);
Button getC = (Button) findViewById(R.id.getCb);
showC.setTitle("C Value");
getC.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
showC.setMessage("C: " + quad.getC());
showC.show();
}
});
final Builder showSF = new AlertDialog.Builder(this);
Button getSF = (Button) findViewById(R.id.getSFb);
showSF.setTitle("Standard Form");
getSF.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
showSF.setMessage("Stand. Form: " + quad.getStandardForm());
showSF.show();
}
});
}
}
XML有3个edittext字段，其编号为numberSigned以允许使用负数。然后有几个按钮，当单击它们时，将显示Quadratic类中的方法。 ：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/RelativeLayout1"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<EditText
android:id="@+id/entA"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:hint="@string/ahint"
android:inputType="numberSigned" >
<requestFocus />
</EditText>
<EditText
android:id="@+id/entB"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_below="@+id/entA"
android:hint="@string/bhint"
android:inputType="numberSigned" />
<EditText
android:id="@+id/entC"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_below="@+id/entB"
android:hint="@string/chint"
android:inputType="numberSigned" />
<Button
android:id="@+id/btnSave"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_below="@+id/entC"
android:text="@string/savebutton" />
<Button
android:id="@+id/getXb"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_below="@+id/btnSave"
android:text="@string/getX" />
<Button
android:id="@+id/getAb"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:layout_below="@+id/entC"
android:text="@string/getA" />
<Button
android:id="@+id/getCb"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:layout_below="@+id/getXb"
android:text="@string/getC" />
<Button
android:id="@+id/getBb"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:layout_below="@+id/getAb"
android:text="@string/getB" />
<Button
android:id="@+id/getYb"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="@+id/getCb"
android:layout_alignBottom="@+id/getCb"
android:layout_alignParentLeft="true"
android:text="@string/getY" />
<Button
android:id="@+id/getSFb"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_below="@+id/getYb"
android:text="@string/getSF" />
</RelativeLayout>
二次类。在此类中，二次方。有几种方法可以调用不同的方法来执行或讲述二次函数。在android活动中，每个函数都将调用该类。
package com.bensherman.quadroid;
public class Quadratic {
private double a, b, c, y, x, s;
public Quadratic()
{
a = 1;
b = 2;
c = -1;
}
public Quadratic (double myA, double myB, double myC)
{
a = myA;
b = myB;
c = myC;
}
public double getA()
{
return a;
}
public double getB()
{
return b;
}
public double getC()
{
return c;
}
public double getSolution1()
{
return (-(b) + Math.sqrt((Math.pow(b, 2))-4*a*c))/(2*a);
}
public double getSolution2()
{
return (-(b) - Math.sqrt((Math.pow(b, 2))-4*a*c))/(2*a);
}
public double getXvalue()
{
return (-b)/(2*a);
}
public double getYvalue()
{
return (a*(Math.pow(x,2))) + (b*x) + c;
}
public String getStandardForm()
{
if (c < 0){
return a + "x^2 + " + b + "x " + c;
}
else
{
return a + "x^2 + " + b + "x +" + c;
}
}
}
最佳答案
当您在onCreate中调用final Quadratic quad = new Quadratic(a, b, c);时，ab和c尚未初始化，因此它们始终为0。在按钮处理程序中的代码直到按下按钮后才会执行，即使它们出现在final Quadratic quad = new Quadratic(a, b, c);行之前源，尚未执行。
除此之外，即使您执行了a，b和c操作，它们仍然会被初始化，因为您声明的局部变量具有相同的名称并分配给它们，而不是使用已经定义的实例变量。
您可以做的是将quad从局部变量移动到实例变量。然后，当您从编辑文本更新a，b，c时，可以在按钮处理程序中将其重新初始化：
public class QuadraticdroidActivity extends Activity {
private Quadratic quad;
private EditText entA, entB, entC;
float a, b, c;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
SharedPreferences QuadPref = this.getSharedPreferences("QUADROID", MODE_PRIVATE);
final SharedPreferences.Editor QuadEdit = QuadPref.edit();
a = QuadEdit.getFloat("a",0f);
b = QuadEdit.getFloat("b",0f);
c = QuadEdit.getFloat("c",0f);
//initialize here since the initialization in the button handler won't happen until someone clicks the button
quad = new Quadtratic (a,b,c);
Button savenum = (Button) findViewById(R.id.btnSave);
savenum.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
entA = (EditText) findViewById(R.id.entA);
//got rid of the "float" here so now we're referring to the instance variable instead of a local
a = Float.parseFloat(entA.getText().toString());
QuadEdit.putFloat("a", a).commit();
entB = (EditText) findViewById(R.id.entB);
b = Float.parseFloat(entB.getText().toString());
QuadEdit.putFloat("b", b).commit();
entC = (EditText) findViewById(R.id.entC);
c = Float.parseFloat(entC.getText().toString());
QuadEdit.putFloat("c", c).commit();
quad = new Quadratic(a,b,c);
}
});
关于android - EditText float 不返回值，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/8358139/