Beginning Android 4 中 Demo Basic/Switch 的问题.

作者的版本:

layout (main.xml):

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="fill_parent"

    android:layout_height="fill_parent"

    android:orientation="vertical" >

    <Switch

        android:id="@+id/switchdemo"

        android:layout_width="fill_parent"

        android:layout_height="wrap_content"

        android:text="WTF?" />

</LinearLayout>

java代码:

public class SwitchActivity extends Activity

  implements CompoundButton.OnCheckedChangeListener {

  Switch sw;

  @Override

  public void onCreate(Bundle icicle) {

    super.onCreate(icicle);

    setContentView(R.layout.main);

    sw=(Switch)findViewById(R.id.switchdemo);

    sw.setOnCheckedChangeListener(this);

  }

//  @Override

  public void onCheckedChanged(CompoundButton buttonView,

                                 boolean isChecked) {

    if (isChecked) {

      sw.setTextOn("This switch is: on");

    }

    else {

      sw.setTextOff("This switch is: off");

    }

  }

}

作者提供的 java 代码有问题. 原因参考(http://stackoverflow.com/questions/29811646/android-settexton-not-working-in-oncheckchanged-method)

I don't think your calls to setTextOn and setTextOff need to be in an if - they just define how the toggle appears when on or off, so they don't need to be set conditionally. Ref: API – Simon MᶜKenzie Apr 23 '15 at 1:01

The setTextOn and setTextOff functions are to used to set the labels depending on the state of the Switch.

The text "The switch is: On" is just the label of your Switch and does not convey the state of your Switch.

To achieve the result that you want, you need to call setShowText(true):
sw = (Switch)findViewById(R.id.swish);

sw.setShowText(true);
or you can add it in your XML.
<Switch

        android:layout_width="453dp"

        android:layout_height="100dp"

        android:id="@+id/swish"

        android:layout_gravity="center_vertical"

        android:layout_alignParentTop="true"

        android:showText="true"/>
As observed by @Simon M, this xml and java snippet produce consistent output as shown by the screen below.
<Switch

    android:layout_width="453dp"

    android:layout_height="100dp"

    android:id="@+id/swish"

    android:layout_gravity="center_vertical"

    android:textOn="ON!!"

    android:textOff="OFF!"

    android:layout_alignParentTop="true"

    android:layout_centerHorizontal="true"/>

    sw = (Switch)findViewById(R.id.swish);

    sw.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {

        @Override

        public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {

          // absolutely nothing

        });
 

答案说的很清楚了. 只需要在 onCreate 里面调用 setTextOn/Off 即可. onCheckedChanged 什么都不用做. 或者根本步调用 setTextOn/Off, 直接在 main.xml 中用 `android::textOn/Off`即可.

下面是修改后的 java 实现, 没有修改 main.xml, 也展示了 setText 与 setTextOn/Off 的区别.

public class SwitchActivity extends ActionBarActivity implements CompoundButton.OnCheckedChangeListener {

    Switch sw;

    @Override

    public void onCreate(Bundle icicle) {

        super.onCreate(icicle);

        setContentView(R.layout.main);

        sw=(Switch)findViewById(R.id.switchdemo);

        sw.setOnCheckedChangeListener(this);

        sw.setTextOff("#OFF#");

        sw.setTextOn("#ON#");

    }

    public void onCheckedChanged(CompoundButton buttonView,

                                 boolean isChecked) {

        if (isChecked) {

            sw.setText("I'm On.");

        } else {

            sw.setText("I'm Off.");

        }

    }

}

巴特西

Beginning Android 4 中 Demo Basic/Switch 的问题.

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