java - 如何在另一种方法中使用 findViewById 变量。 Java 安卓

Question

我是编程新手，正在自学，如果我的代码难看，我深表歉意。

我正在尝试创建一个类似屏幕的菜单，它具有左右箭头按钮，可以更改显示的图片。我想做到这一点，当您在第一张图片上显示左箭头时，在显示最后一张图片时，右箭头消失。

我已经尝试过很多不同的方法来做到这一点，但最终总是需要一个无法解析的地方的变量。在发布的代码中，错误出现在 switch 语句中，我尝试用其他方式对其进行编码， Unresolved 变量错误将出现在 onClickListener 中。

您不必为我编写代码，只需让我知道我缺少什么概念，我会研究它。

谢谢

    package com.mystuff.mymenu;

    import android.app.Activity;
    import android.os.Bundle;
    import android.view.View;
    import android.view.View.OnClickListener;
    import android.widget.ImageButton;
    import android.widget.ImageView;



public class PictureMenu extends Activity implements OnClickListener{

int setView = 1;    

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.picture_menu);  

    menuSet(setView);

ImageButton right = (ImageButton) findViewById(R.id.rightButton);
ImageButton left = (ImageButton) findViewById(R.id.leftButton);
right.setOnClickListener(this);
left.setOnClickListener(this);

}       
@Override
public void onClick(View v) {
if(v.getId() == R.id.rightButton){
    setView ++;
    menuSet(setView);
if(v.getId() == R.id.rightButton){
    setView ++;
        menuSet(setView);
}
    }   
    }


private void menuSet(int setView) {

    ImageView picture1 = (ImageView) findViewById(R.id.picture1);
    ImageView picture2 = (ImageView) findViewById(R.id.picture2);
    ImageView picture3 = (ImageView) findViewById(R.id.picture3);
    ImageView picture4 = (ImageView) findViewById(R.id.picture4);

    switch(setView){
    case 1: 
        left.setVisibility(View.GONE);  //ERROR left cannot be resolved
        right.setVisibility(View.VISIBLE); //ERROR right cannot be resolved
        picture1.setVisibility(View.VISIBLE);
        picture2.setVisibility(View.GONE);
        picture3.setVisibility(View.GONE);
        picture4.setVisibility(View.GONE);
        break;
    case 2:
        left.setVisibility(View.VISIBLE);  //ERROR left cannot be resolved
        right.setVisibility(View.VISIBLE);  //ERROR right cannot be resolved
        picture1.setVisibility(View.GONE);
        picture2.setVisibility(View.VISIBLE);
        picture3.setVisibility(View.GONE);
        picture4.setVisibility(View.GONE);
        break;
    case 3: 
        left.setVisibility(View.VISIBLE);  //ERROR left cannot be resolved
        right.setVisibility(View.VISIBLE);  //ERROR right cannot be resolved
        picture1.setVisibility(View.GONE);
        picture2.setVisibility(View.GONE);
        picture3.setVisibility(View.VISIBLE);
        picture4.setVisibility(View.GONE);
        break;
    case 4: 
        left.setVisibility(View.VISIBLE); //ERROR left cannot be resolved
        right.setVisibility(View.GONE); //ERROR right cannot be resolved
        picture1.setVisibility(View.GONE);
        picture2.setVisibility(View.GONE);
        picture3.setVisibility(View.GONE);
        picture4.setVisibility(View.VISIBLE);
        break;
    default:
        left.setVisibility(View.GONE);  //ERROR left cannot be resolved
        right.setVisibility(View.VISIBLE);  //ERROR right cannot be resolved
        picture1.setVisibility(View.VISIBLE);
        picture2.setVisibility(View.GONE);
        picture3.setVisibility(View.GONE);
        picture4.setVisibility(View.GONE);
        break;
}       


}



}

Answer 1

您的问题在于 right 和 left 是 onCreate() 方法的局部值，无法从该方法外部看到。如果你想要它们在类范围内，使它们成为类属性，例如:

public class PictureMenu extends Activity implements OnClickListener {

    int setView = 1; 
    ImageButton right, left;
    ...

    protected void onCreate(Bundle savedInstanceState) {
        ...
        right = (ImageButton) findViewById(R.id.rightButton);
        left = (ImageButton) findViewById(R.id.leftButton);
        ...
    }

另一个解决方案是将它们作为参数传递给 menuSet()

恕我直言，你应该首先学习正确的编程，特别是什么 variable scope是。 此外，正确格式化您的代码有助于轻松发现范围。