Android：创建“自定义3状态”切换按钮时出现问题

我试图通过覆盖Button类来创建3状态切换按钮.

尽管代码中没有错误,但是Eclipse在布局xml中显示了以下问题.

以下类无法实例化：

- com.example.threewaytoggle.TriToggleButton (Open Class, Show Error Log)
See the Error Log (Window > Show View) for more details.
Tip: Use View.isInEditMode() in your custom views to skip code when shown in Eclipse

在错误日志中,这即将到来：

com.example.threewaytoggle.TriToggleButton failed to instantiate.

java.lang.NullPointerException
at android.view.View.mergeDrawableStates(View.java:7506)
at com.example.threewaytoggle.TriToggleButton.onCreateDrawableState(TriToggleButton.java:42)
at android.view.View.getDrawableState(View.java:7410)
at android.view.View.setBackgroundDrawable(View.java:7583)....

以下是代码：
布局xml：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <com.example.threewaytoggle.TriToggleButton
        android:id="@+id/triToggleButton1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="TriToggleButton" />
</LinearLayout>

自定义按钮类别：

package com.example.threewaytoggle;

import android.content.Context;
import android.util.AttributeSet;
import android.widget.Button;

public class TriToggleButton extends Button {

    int _state = 0;
    public TriToggleButton(Context context) {
        super(context);
        _state = 0;
        this.setText("1");
    }

    public TriToggleButton(Context context, AttributeSet attrs) {
        super(context, attrs);
        _state = 0;
        this.setText("1");
    }

    public TriToggleButton(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        _state = 0;
        this.setText("1");
    }

    private final int[] STATE_ONE_SET = { R.attr.state_one };
    private final int[] STATE_TWO_SET = { R.attr.state_two };
    private final int[] STATE_THREE_SET = { R.attr.state_three };

    @Override
    protected int[] onCreateDrawableState(int extraSpace) {
        final int[] drawableState = super.onCreateDrawableState(extraSpace + 3);

        if (_state == 0) {
            mergeDrawableStates(drawableState, STATE_ONE_SET);
        } else if (_state == 1) {
            mergeDrawableStates(drawableState, STATE_TWO_SET);
        } else if (_state == 2) {
            mergeDrawableStates(drawableState, STATE_THREE_SET);
        }

        return drawableState;
    }

    @Override
    public boolean performClick() {
        nextState();
        return super.performClick();
    }

    private void nextState() {
        _state++;
        if (_state > 2) {
            _state = 0;
        }
        setButtonText();
    }

    private void setButtonText() {
        //TODO      
    }

    public int getState() {
        return _state;
    }
}

解决方法:

找到了…

private static final int[] STATE_ONE_SET = { R.attr.state_one };
private static final int[] STATE_TWO_SET = { R.attr.state_two };
private static final int[] STATE_THREE_SET = { R.attr.state_three };

但是,这怎么会引起问题呢？

标签：android-layout,android-custom-view,android
来源： https://codeday.me/bug/20191127/2076003.html