An Android Toast is a small message displayed on the screen, similar to a tool tip or other similar popup notification. A Toast is displayed on top of the main content of an activity, and only remains visible for a short time period. This screenshot shows how a Toast looks like on the screen:
The Toast is shown at the bottom of the screen in the above screenshot (but you can change that).
Creating a Toast
Here is an Android Toast example:
Toast toast = Toast.makeText(getApplicationContext(),
"This is a message displayed in a Toast",
Toast.LENGTH_SHORT);
toast.show();
The Toast.makeText() method is a factory method which creates a Toast object. The method takes 3 parameters. First the methods needs a Context object which is obtained by calling getApplicationContext(). Note: The getApplicationContext() method is a method that exists inside activities, so the above code has to be located in an Activity subclass to work.
The second parameter is the text to be displayed in the Toast. The third parameter is the time duration the Toast is to be displayed. The Toast class contains two predefined constants you can use: Toast.LENGTH_SHORT and Toast.LENGTH_LONG. You will have to experiment with these two values to see which fits your situation better.
Toast Positioning
You can change the positioning on the screen of a Toast message using the setGravity() method. Here is a Toast setGravity() example:
toast.setGravity(Gravity.CENTER, 0, 0);
The first parameter of the setGravity() method specifies the overall position of the Toast. You can use the following constants in the Gravity class to specify the overall position:
TOPBOTTOMLEFTRIGHTCENTERCENTER_HORIZONTALCENTER_VERTICAL
Each of these constants defines the position in either the X or Y direction, except for the CENTER constant which implies centered both horizontally and vertically. You can combine these constants using the | (or) operator, like this:
toast.setGravity(Gravity.TOP | Gravity.CENTER_HORIZONTALLY, 0, 0);
The two other parameters of the setGravity() method are an X and Y offset to the position defined by the Gravity constant. If, for instance, you need the Toast to be displayed at the top, centered horizontally, but 20 pixels down from the top position, you would use this setGravity() call:
toast.setGravity(Gravity.TOP | Gravity.CENTER_HORIZONTALLY, 0, 20);
Toast Custom Views
It is possible to define a custom View for your Toast. To do so, first you must create a layout XML file for the custom View. Here is an example Toast layout XML file:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/toast_root_view"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@android:color/background_dark"
android:padding="16dp"
>
<TextView
android:id="@+id/toast_header"
android:textSize="20dp"
android:textColor="@android:color/primary_text_dark"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<TextView
android:id="@+id/toast_body"
android:textColor="@android:color/primary_text_dark"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</LinearLayout>
Put this layout XML file into your Android project’s /app/src/main/res/layout directory and name the file my_toast.xml .
To use this layout XML file with a Toast you write this code:
LayoutInflater inflater = getLayoutInflater();
View toastLayout = inflater.inflate(R.layout.my_toast,
(ViewGroup) findViewById(R.id.toast_root_view));
TextView header = (TextView) toastLayout.findViewById(R.id.toast_header);
header.setText("Message for you:");
TextView body = (TextView) toastLayout.findViewById(R.id.toast_body);
body.setText("You have got mail!");
Toast toast = new Toast(getApplicationContext());
toast.setGravity(Gravity.CENTER, 0, 0);
toast.setDuration(Toast.LENGTH_LONG);
toast.setView(toastLayout);
toast.show();
First you obtain the LayoutInflater. You use that to inflate (create) the View defined by your the layout XML file named my_toast.xml (referred to by R.layout.my_toast).
Notice the findViewById(R.id.toast_root_view) call as the second parameter to the inflate() method call. This finds the root ViewGroup in the my_toast.xml layout XML file (the root ViewGroup has the id toast_view_group). This call is necessary for the inflated View to know what the root ViewGroup inside the inflated View is.
Once the View is created, you obtain the two TextView components from the View and set their texts.
Finally, you create a Toast object, set its gravity (position / alignment), its duration, its View and then show it.
Here is how the Toast above looks when displayed:
谢嘉琪 