我试图通过添加值txtA + txtB来计算名为lblAnswer的字段。我是Android开发世界的新手，想知道最好的方法是什么。我已经将必要的编辑字段添加到GUI。我现在正在java文件中尝试创建该方法。此方法已命名为doCalc。这是我到目前为止所拥有的。
public void doCalc()
{
lblAnswer = txtA + txtB;
}
有人建议我在这里添加更多代码是完整代码。谢谢你的建议。
这是Java文件。
package com.example.wattsprofessional;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
public class MainActivity extends Activity {
@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.activity_main, menu);
return true;
}
public void doCalc()
{
lblAnswer = txtA + txtB;
Double.parseDouble(txtA.getText().toString());
lblAnswer.setText"t
}
这是xml文件。
<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"
tools:context=".MainActivity" >
<EditText
android:id="@+id/txtA"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="40dp"
android:ems="10"
android:hint="Write Here"
android:inputType="numberDecimal" >
<requestFocus />
</EditText>
<EditText
android:id="@+id/txtB"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/txtA"
android:layout_below="@+id/txtA"
android:layout_marginTop="32dp"
android:ems="10"
android:hint="Second Here"
android:inputType="numberDecimal" />
<Button
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:text="@string/calculate"
android:onClick="doCalc"/>
<TextView
android:id="@+id/lblAnswer"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/button1"
android:layout_centerHorizontal="true"
android:layout_marginTop="50dp"
android:text="TextView" />
</RelativeLayout>
答案 0 :(得分：1)
要从EditText获取Double值，您需要使用Double.parseDouble(txtA.getText().toString())。要设置文字，您可以使用lblAnswer.setText("text")。
此外，从按钮调用此方法的最简单方法是在XML中设置其android:onClick属性，例如android:onClick="doCalc"。
编辑：您还需要创建对象的引用。在你的onCreate（）之前，把：
EditText txtA;
EditText txtB;
TextView lblAnswer;
然后在你的onCreate（）中你需要初始化对象：
txtA = new (EditText)findViewById(R.Id.txtA);
txtB = new (EditText)findViewById(R.Id.txtB);
lblAnswer = new (TextView)findViewById(R.Id.lblAnswer);
答案 1 :(得分：1)
您的代码缺少一些关键组件。检查您的代码，并查看我在下面准备的代码。
package com.example.wattsprofessional;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class MainActivity extends Activity {
private EditText txtA, txtB;
private Button button1;
// ^ we have declared these as fields up here so that we can access them throughout the page, past all the curly brackets
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
txtA = (EditText) findViewById(R.id.txtA);
txtB = (EditText) findViewById(R.id.txtB);
button1 = (Button) findViewById(R.id.button1);
// ^ this is where we initialize these. You did the xml correctly, but you still need to hook the java to it.
// it allows us to use any names and locations we like not just same ones.
// basically you say what it is (Button) and then use the following method to look for the id that you wrote in the xml
initButton();
// i made this listener so we'd have time. this is the oncreate method and is called instantly.
// if we called doCalc here, we'd have no time to put numbers in.
}
private void initButton() {
button1.setOnClickListener(new OnClickListener() {
// this one performs an action when our button is clicked. it performs whatever is below
@Override
public void onClick(View v) {
String strA = txtA.getText().toString();
String strB = txtB.getText().toString();
// we get our strings from our editexts. i think you know how to do this well.
Double dblAnswer = doCalc(strA, strB);
// ^we pass them to our method, it does all the heavy lifting for us. and spits an answer for us.
TextView lblAnswer = (TextView) findViewById(R.id.lblAnswer);
// this is a local variable, as opposed to a field. i made so you know that you can do it like this - with the whole line here
// the disadvantage is that we can't do anything to it outside of this curly bracket. but there are performs gains.
// in general it's wasteful to use fields when you can suffice with local variable
String answer = String.valueOf(dblAnswer);
// we get our answer and turn it to a string.
lblAnswer.setText(answer);
// finally we set our result to the textView.
}
});
}
public double doCalc(String a, String b) {
// a and b are both variables. they refer to the stuff we put in
double dblA = Double.parseDouble(a);
double dblB = Double.parseDouble(b);
// we're gonna make both of these numbers so we can add them. right now they're just text.
return dblA + dblB;
// ^ this statement means that this method will spit a number out when it's done which we can use however.
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
}