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Android中的回调

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Android中的回调,android,callback,Android,Callback,我对Android和整个编程都是新手，我需要一些回调方面的帮助。我理解回调的要点，但我不确定如何着手实施 上下文：我正在编写一个简单的记事本应用程序，允许用户编写文本并将其保存到应用程序中。然后，用户可以通过按钮请求读取文件。然后，文本将显示在主活动的文本视图中。有一个选项可以擦除此文件，这是通过确认弹出窗口完成的，这是另一个活动。此弹出窗口包含两个按钮，一个用于取消，一个用于擦除。如果文件不为空，它将擦除，如果为空，则不执行任何操作。我不确定这是否是实现它的最佳方式，但我想使用wipe按钮回调

我对Android和整个编程都是新手，我需要一些回调方面的帮助。我理解回调的要点，但我不确定如何着手实施

上下文：我正在编写一个简单的记事本应用程序，允许用户编写文本并将其保存到应用程序中。然后，用户可以通过按钮请求读取文件。然后，文本将显示在主活动的文本视图中。有一个选项可以擦除此文件，这是通过确认弹出窗口完成的，这是另一个活动。此弹出窗口包含两个按钮，一个用于取消，一个用于擦除。如果文件不为空，它将擦除，如果为空，则不执行任何操作。我不确定这是否是实现它的最佳方式，但我想使用wipe按钮回调到主活动以清除textview。我想到的方法是使用回调函数返回一个布尔值。主活动将检查布尔值是否为真，如果为真，则清除textview。我不确定如何在弹出显示中实现回调以将此布尔值发送回主活动

主要活动的代码

public class MainActivity extends AppCompatActivity implements Popout.ClearTextView {

    Button bnRead,bnWrite,bnClear;
    TextView tvFileOP;
    EditText etInput;
    //    private static final String INPUT_CONTENT = "inputContent";
    public static final String  TV_CONTENT = "textViewContent";

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

        bnRead = (Button) findViewById(R.id.bnRead);
        bnWrite = (Button) findViewById(R.id.bnWrite);
        bnClear = (Button) findViewById(R.id.bnClear);

        tvFileOP = (TextView) findViewById(R.id.tvFileOP);
        etInput = (EditText) findViewById(R.id.etInput);
        tvFileOP.setMovementMethod(new ScrollingMovementMethod());

        final String fileName = "test_file";
        String data;

        bnRead.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                try {
                    FileInputStream fIn = openFileInput(fileName);
                    int c;
                    String temp = "";
                    while ( (c=fIn.read()) != -1){
                        temp = temp + Character.toString((char) c);
                    }
                    tvFileOP.setText(temp);
                    Toast.makeText(getBaseContext(),"file successfully read", Toast.LENGTH_LONG).show();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });

        bnWrite.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String data = etInput.getText().toString();
                try {
                    FileOutputStream fOut = openFileOutput(fileName,MODE_APPEND);
                    fOut.write(data.getBytes());
                    fOut.close();
                    etInput.setText("");
                    Toast.makeText(getBaseContext(),"file successfully written", Toast.LENGTH_LONG).show();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });

        bnClear.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(MainActivity.this,Popout.class));
            }
        });

    }

    @Override
    protected void onSaveInstanceState(@NonNull Bundle outState) {
        outState.putString(TV_CONTENT,tvFileOP.getText().toString());
        super.onSaveInstanceState(outState);
    }

    @Override
    protected void onRestoreInstanceState(@NonNull Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);
        tvFileOP.setText(savedInstanceState.getString(TV_CONTENT));
    }


    @Override
    public void clearTextView(Boolean clear) {
        if (clear){
            tvFileOP.setText("");
        }
    }
}
弹出确认菜单的代码

public class Popout extends AppCompatActivity {

    Button bnClosepopup,bnWipe;
    TextView tvConfirmation;
    String fileName = "test_file";
    TextView tvFileOP;

    public interface ClearTextView {
        public void clearTextView(Boolean clear);
    }

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

        bnClosepopup = (Button) findViewById(R.id.bnClosepopup);
        bnWipe = (Button) findViewById(R.id.bnWipe);
        tvConfirmation = (TextView) findViewById(R.id.tvConfirmation);


        //HIDING THE TOOL BAR AT THE TOP OF THE SCREEN
        this.getSupportActionBar().hide();

        //GETTING THE SIZE OF THE SCREEN
        DisplayMetrics displayMetrics = new DisplayMetrics();
        getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
        int height = displayMetrics.heightPixels;
        int width = displayMetrics.widthPixels;
        getWindow().setLayout((int) (width*0.8) , (int) (0.8*height));

        bnClosepopup.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                finish();
            }
        });

        bnWipe.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                try {
                    File dir = getFilesDir();
                    File file = new File(dir, fileName);
                    boolean deleted = file.delete();
                    Toast.makeText(getBaseContext(),"file has been deleted",Toast.LENGTH_SHORT).show();

                } catch (Exception e) {
                    Toast.makeText(getBaseContext(), e.getMessage(), Toast.LENGTH_LONG).show();
                }
                finish();

            }
        });
    }
}
我对android开发非常陌生，任何关于如何改进代码的提示都将不胜感激：）

在这种情况下，无法将界面传递给其他活动，因为这是一种活动对活动的交流

您必须使用其他方法，有多种方法可供选择，我能想到的最佳方法是使用
startActivityForResult（）
启动活动，然后等待响应返回，然后通过覆盖
onActivityResult（）
方法在
MainActivity
中查询此响应：

示例 在
main活动中
：

    //on click of this button
    bnClear.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            Intent intent = new Intent(MainActivity.this,Popout.class);
            int requestCode = 12; //it could be whatever you want
            startActivityForResult(intent , requestCode);

        }
    });


//override this method


@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);

//this is triggered when you finish the Popout Activity
if(requestCode == 12 && resultCode == Activity.RESULT_OK){

// get the boolean data returned from the Popout Activity
boolean deleted = data.getBooleanExtra("deleted_state" , false); //false is default if no value exists

}


}

    bnWipe.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            try {
                File dir = getFilesDir();
                File file = new File(dir, fileName);
                boolean deleted = file.delete();

                //send the result to onActivtyResult() in MainActivity
                Intent result = new Intent();
                result.putExtra("deleted_state", deleted ); 
                setResult(Activity.RESULT_OK, result);

                Toast.makeText(getBaseContext(),"file has been deleted",Toast.LENGTH_SHORT).show();

            } catch (Exception e) {
                Toast.makeText(getBaseContext(), e.getMessage(), Toast.LENGTH_LONG).show();
            }
            finish();

        }
    });
在
弹出窗口中
活动：

    //on click of this button
    bnClear.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            Intent intent = new Intent(MainActivity.this,Popout.class);
            int requestCode = 12; //it could be whatever you want
            startActivityForResult(intent , requestCode);

        }
    });


//override this method


@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);

//this is triggered when you finish the Popout Activity
if(requestCode == 12 && resultCode == Activity.RESULT_OK){

// get the boolean data returned from the Popout Activity
boolean deleted = data.getBooleanExtra("deleted_state" , false); //false is default if no value exists

}


}

    bnWipe.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            try {
                File dir = getFilesDir();
                File file = new File(dir, fileName);
                boolean deleted = file.delete();

                //send the result to onActivtyResult() in MainActivity
                Intent result = new Intent();
                result.putExtra("deleted_state", deleted ); 
                setResult(Activity.RESULT_OK, result);

                Toast.makeText(getBaseContext(),"file has been deleted",Toast.LENGTH_SHORT).show();

            } catch (Exception e) {
                Toast.makeText(getBaseContext(), e.getMessage(), Toast.LENGTH_LONG).show();
            }
            finish();

        }
    });
更新：

    //on click of this button
    bnClear.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            Intent intent = new Intent(MainActivity.this,Popout.class);
            int requestCode = 12; //it could be whatever you want
            startActivityForResult(intent , requestCode);

        }
    });


//override this method


@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);

//this is triggered when you finish the Popout Activity
if(requestCode == 12 && resultCode == Activity.RESULT_OK){

// get the boolean data returned from the Popout Activity
boolean deleted = data.getBooleanExtra("deleted_state" , false); //false is default if no value exists

}


}

    bnWipe.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            try {
                File dir = getFilesDir();
                File file = new File(dir, fileName);
                boolean deleted = file.delete();

                //send the result to onActivtyResult() in MainActivity
                Intent result = new Intent();
                result.putExtra("deleted_state", deleted ); 
                setResult(Activity.RESULT_OK, result);

                Toast.makeText(getBaseContext(),"file has been deleted",Toast.LENGTH_SHORT).show();

            } catch (Exception e) {
                Toast.makeText(getBaseContext(), e.getMessage(), Toast.LENGTH_LONG).show();
            }
            finish();

        }
    });
它将是这样的：

// get the boolean data returned from the Popout Activity
boolean deleted = data.getBooleanExtra("deleted_state" , false);
    if (deleted){
        tvFileOP.setText("");
    }
..........
就正确理解您的问题而言：您希望从活动中控制“擦除”按钮单击事件。以下是可能对您有所帮助的解决方案

1：为对话框类创建一个重写的构造函数

2：在dialog类中创建一个抽象方法。（说-onWipeButtonClick） 您还需要将对话框类抽象化

3：在“擦除”按钮的侦听器中单击，调用“擦除”按钮单击抽象方法

4：根据需要在主活动中创建dialog实例。编译器将给您一个错误，因为您尚未实现回调方法。 执行onWipeButtonClick方法，并对方法中的擦除数据执行必要的操作

public abstract class WipeDialog extends Dialog{

private Context context;

  public WipeDialog(Context context){
   this.context = context;
  }

 public abstract void onWipeButtonClick(boolean isTextEmpty); 

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

    <initialization>

    btnWipe.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            onWipeButtonClick(<YOUR_BOOLEAN_CHECK>);
        }
    });
 }
}
希望这会有所帮助。
谢谢

非常感谢您的回复，但我想知道是否有更简单的方法来解决我的问题。是否有一种我不知道的更简单的方法来实现此功能？对于您的情况，此解决方案是为此类事情构建此方法的最推荐方法，是的，通过的
deleted
是您用来检查的。在看到此评论之前，我只是设法弄明白了。非常感谢你的帮助！如果这有助于接受答案，那么其他有同样问题的人就知道该去哪里找了，那就太好了。祝你好运。我不知道对话是一种东西，谢谢你把这件事告诉我。我会研究使用它们的！很高兴帮助你！：）