android:visibility="visible/invisible/gone"

public class MainActivity extends AppCompatActivity implements View.OnClickListener{
 
    	@Override
    	protected void onCreate(Bundle savedInstanceState) {
        	super.onCreate(savedInstanceState);
        	setContentView(R.layout.activity_main);
 
        	Button button = findViewById(R.id.button_useful);
        	button.setOnClickListener(this);
    	}
 
 
    	@Override
    	public void onClick(View view) {
 
       	 	switch (view.getId()){
            	case R.id.button_useful:
                	AlertDialog.Builder dialog = new AlertDialog.Builder(this);
                	dialog.setTitle("This is dialog");
                	dialog.setMessage("Something important.");
                	dialog.setCancelable(false);
                	dialog.setPositiveButton("OK", new DialogInterface.OnClickListener() {
                    	@Override
                    	public void onClick(DialogInterface dialogInterface, int i) {
 
                    	}
               		});
                	dialog.setNegativeButton("cancel", new DialogInterface.OnClickListener() {
                   		@Override
                    	public void onClick(DialogInterface dialogInterface, int i) {
 
                    	}
                	});
                	dialog.show();
                	break;
            	default:
               		break;
        	}
    	}
	}

case R.id.button_progress_dialog:
        ProgressDialog progressDialog = new ProgressDialog(this);
        progressDialog.setTitle("This is ProgressDialog");
        progressDialog.setMessage("Loading...");
        progressDialog.setCancelable(true);
        progressDialog.show();
        break;

public void buttonToImage(View view) {
 
    Toast toast = new Toast(this);
    ImageView imageView = new ImageView(this);
 
    //設(shè)置圖片
    imageView.setImageResource(R.drawable.head);
 
    //顯示圖片
    toast.setView(imageView);
    toast.setDuration(Toast.LENGTH_LONG);
 
    //設(shè)置圖片位置
    toast.setGravity(Gravity.TOP,0,0);
    toast.show();
}

public void buttonToBoth(View view) {
 
    Toast toast = new Toast(this);
 
    TextView textView = new TextView(this);
    textView.setText("這是頭像");
    textView.setGravity(Gravity.CENTER);
    textView.setTextSize(20);
 
    ImageView imageView = new ImageView(this);
    imageView.setImageResource(R.drawable.head);
 
    //組合
    LinearLayout layout = new LinearLayout(this);
    //設(shè)置垂直
    layout.setOrientation(LinearLayout.VERTICAL);
    //設(shè)置居中
    layout.setGravity(Gravity.CENTER);
    layout.addView(imageView);
    layout.addView(textView);
 
    toast.setView(layout);
    toast.setGravity(Gravity.TOP,0,0);
    toast.setDuration(Toast.LENGTH_LONG);
    toast.show();
}

<item android:id="@+id/item_add"
      android:title="Add" />

@Override
public boolean onCreateOptionsMenu(Menu menu) {
  	getMenuInflater().inflate(R.menu.main,menu);
  	return true;
}

@Override
public boolean onOptionsItemSelected(@NonNull MenuItem item) {
        
    switch(item.getItemId()){
        case R.id.item_add:
            Toast.makeText(this,"You click Add",Toast.LENGTH_SHORT).show();
            break;
        case R.id.item_remove:
            Toast.makeText(this,"You click Remove",Toast.LENGTH_SHORT).show();
            break;
        default:
            break;
    }
 
    return true;
}