Android中具有MultipleItemSelection的警报对话框

在上一篇文章Android中带有SingleItemSelection的Alert对话框中，我们看到了如何为单个项目选择构建警报对话框。在本文中，已经讨论了如何构建具有多个项目选择的警报对话框。当用户想要一次选择多个项目时，将使用“多个项目选择”对话框。查看下图，以区分“单项选择”和“多项选择”警告对话框。

实现具有多个项目选择的警报对话框的步骤

步骤1：创建一个空的活动项目

• 创建一个空的活动Android Studio项目。并选择Java作为编程语言。
• 要创建一个空的活动Android Studio项目，请参考Android |如何在Android Studio中创建/启动新项目?

步骤2：使用activity_main.xml

• 主要布局包括一个简单的Button和一个TextView小部件。实现TextView可以预览列表中的选定项目。
• 调用以下代码以构建UI：

输出界面：

步骤3：使用MainActivity。 Java文件

• 有必要了解多项目选择警报对话框的各个部分。查看下图以了解各部分：

• 下面讨论需要为警报对话框选择多个项目的函数。

Syntax:

setMultiChoiceItems(listItems, checkedItems, new DialogInterface.OnMultiChoiceClickListener()

Parameters:

listItems: are the items to be deisplayed on the alert dialog.

checkedItems: it is the boolean array which maintains the selected valus as true, and unselected values as false.

DialogInterface.OnMultiChoiceClickListener(): which is callback when change in the selection of items takes place.

• 调用以下代码实现事物。添加了注释以便更好地理解。

Java

import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;
import android.annotation.SuppressLint;
import android.content.DialogInterface;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import java.util.Arrays;
import java.util.List;
  
public class MainActivity extends AppCompatActivity {
  
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
  
        // UI widgets button and
        Button bOpenAlertDialog = findViewById(R.id.openAlertDialogButton);
        final TextView tvSelectedItemsPreview = findViewById(R.id.selectedItemPreview);
  
        // initialise the list items for the alert dialog
        final String[] listItems = new String[]{"C", "C++", "JAVA", "PYTHON"};
        final boolean[] checkedItems = new boolean[listItems.length];
  
        // copy the items from the main list to the selected item list
        // for the preview if the item is checked then only the item 
          // should be displayed for the user
        final List selectedItems = Arrays.asList(listItems);
  
        // handle the Open Alert Dialog button
        bOpenAlertDialog.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
  
                // initially set the null for the text preview
                tvSelectedItemsPreview.setText(null);
  
                // initialise the alert dialog builder
                AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
                
                // set the title for the alert dialog
                builder.setTitle("Choose Items");
                
                // set the icon for the alert dialog
                builder.setIcon(R.drawable.image_logo);
  
                // now this is the function which sets the alert dialog for multiple item selection ready
                builder.setMultiChoiceItems(listItems, checkedItems, new DialogInterface.OnMultiChoiceClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which, boolean isChecked) {
                        checkedItems[which] = isChecked;
                        String currentItem = selectedItems.get(which);
                    }
                });
  
                // alert dialog shouldn't be cancellable
                builder.setCancelable(false);
  
                // handle the positive button of the dialog
                builder.setPositiveButton("Done", new DialogInterface.OnClickListener() {
                    @SuppressLint("SetTextI18n")
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        for (int i = 0; i < checkedItems.length; i++) {
                            if (checkedItems[i]) {
                                tvSelectedItemsPreview.setText(tvSelectedItemsPreview.getText() + selectedItems.get(i) + ", ");
                            }
                        }
                    }
                });
  
                // handle the negative button of the alert dialog
                builder.setNegativeButton("CANCEL", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
  
                    }
                });
  
                // handle the neutral button of the dialog to clear
                  // the selected items boolean checkedItem
                builder.setNeutralButton("CLEAR ALL", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        for (int i = 0; i < checkedItems.length; i++) {
                            checkedItems[i] = false;
                        }
                    }
                });
  
                // create the builder
                builder.create();
  
                // create the alert dialog with the 
                  // alert dialog builder instance
                AlertDialog alertDialog = builder.create();
                alertDialog.show();
            }
        });
    }
}

输出：在模拟器上运行

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