Question

当我在img1中声明img2和onCreate()变量时，我的问题已解决。但是，我确实需要全局声明这些变量。有什么想法吗？

package com.example.ui;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageView;
import android.widget.Toast;




public class MainActivity extends AppCompatActivity implements View.OnClickListener  {
    /*img1 and img2 veriables below*/
    ImageView img1 = findViewById(R.id.img1);
    ImageView img2 = findViewById(R.id.img2);
    @Override

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        /*my problem is fixed when I declare those variables here, but I need them to be global*/
        img1.setOnClickListener(this);
        img2.setOnClickListener(this);

          }

    @Override
    public void onClick(View view) {
        int id = view.getId();

        switch(id){
            case R.id.img1:
                Toast.makeText(this, "img1", Toast.LENGTH_SHORT).show();
                break;
            case R.id.img2:
                Toast.makeText(this, "img2", Toast.LENGTH_SHORT).show();

        }
    }
}

Answer 1

在将视图附加到班级之前就已经找到了视图

这是正确的方法：

public class MainActivity extends AppCompatActivity implements View.OnClickListener  {
    /*img1 and img2 veriables below*/
    ImageView img1;
    ImageView img2;
    @Override

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

     img1 = findViewById(R.id.img1);
     img2 = findViewById(R.id.img2);

        /*my problem is fixed when I declare those variables here, but I need them to be global*/
        img1.setOnClickListener(this);
        img2.setOnClickListener(this);

          }

    @Override
    public void onClick(View view) {
        int id = view.getId();

        switch(id){
            case R.id.img1:
                Toast.makeText(this, "img1", Toast.LENGTH_SHORT).show();
                break;
            case R.id.img2:
                Toast.makeText(this, "img2", Toast.LENGTH_SHORT).show();

        }
    }
}

Answer 2

修改您的

 ImageView img1;//only declaration
 ImageView img2;
  @Override

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
       ImageView img1 = findViewById(R.id.img1);
      ImageView img2 = findViewById(R.id.img2);
    /*my problem is fixed when I declare those variables here, but I need them to be global*/
    img1.setOnClickListener(this);
    img2.setOnClickListener(this);

      }

Answer 3

您不能在那里使用findViewById，请尝试以下操作：

public class MainActivity extends AppCompatActivity implements 
View.OnClickListener  {
private ImageView img1;
private ImageView img2;
@Override

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    img1 = findViewById(R.id.img1);
    img2 = findViewById(R.id.img2);
    
    img1.setOnClickListener(this);
    img2.setOnClickListener(this);

      }

@Override
public void onClick(View view) {
    int id = view.getId();

    switch(id){
        case R.id.img1:
            Toast.makeText(this, "img1", Toast.LENGTH_SHORT).show();
            break;
        case R.id.img2:
            Toast.makeText(this, "img2", Toast.LENGTH_SHORT).show();

    }
}

Here is the documentation

Answer 4

我真的无法理解您的意思。您是要让img1和img2在活动中还是在应用程序中变得全球化？

实际上，我想您会误解该程序的顺序。在onCreate（）方法之后，电话窗口将被初始化。然后，setContentView（）方法将视图绑定到电话窗口中。因此，应该在setContentView（）之后在onCreate（）方法中绑定imageView。

public class MainActivity extends AppCompatActivity implements View.OnClickListener  {
    /*img1 and img2 veriables below*/
    ImageView img1;
    ImageView img2;
    @Override

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        img1 = findViewById(R.id.img1);
        img2 = findViewById(R.id.img2);
        /*my problem is fixed when I declare those variables here, but I need them to be global*/
        img1.setOnClickListener(this);
        img2.setOnClickListener(this);

          }
}

Answer 5

您应该有以下几行：

ImageView img1 = findViewById（R.id.img1）;

ImageView img2 = findViewById（R.id.img2）;

在“ setContentView（R.layout.activity_main）;”之后的OnCreate方法内部

android studio：启动后我的应用立即崩溃

5 个答案: