Android Drawables
This tutorial describes the usage of Drawables in Android.
Table of Contents
A Drawable resource is a general concept for a graphic which can be drawn. The simplest case is a graphical file (bitmap), which would be represented in Android via a
BitmapDrawable class.Every Drawable is stored as individual files in one of the
res/drawable folders. Typically you would store bitmaps for different resolutions in the -mdpi, -hdpi, -xhdpi, -xxhdpi subfolders of res/drawable. The ADT project creation wizard creates these folders by default. If these bitmaps are provided in different folder, the Android system selects the correct one automatically based on the device configuration.If you do not provide bitmaps for all supported resolutions, the the Android system scales the closest fit up or down. This is typically undesired as the bitmap might get blury.
In addition to graphical files, Android supports XML drawables and 9-patch graphics. XML drawables are used to describe shapes (color, border, gradient), state, transitions and more.
9-patch graphics are used to define which part of a graphic should be stretched if the view which uses this graphic is larger than the graphic.
Drawables can also be written in Java code. Every object which implements
Drawable can be used as a Drawable in code.Drawables are referred to in XML via
@drawable/filename whereby filename filename is the filename without the file extension. For example to access the res/drawable/hello.png Drawable, you would use @drawable/hello as demonstrated in the following snippet.<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="@drawable/hello"
android:text="@string/hello_world" />
In code you can also assign drawables to views. Most views accept an resource ID as input parameter. For example the following code shows how to set a drawables as background to an
ImageView.ImageView imageView = (ImageView) findViewById(R.id.image);
imageView.setImageResource(R.drawable.hello);
Android allows you to use the
Bitmap class for working with bitmaps. This section explain how to create Bitmap objects via Java code and how to convert Bitmap into Drawable objects and vice versa.If required you can load any accessible bitmap file in your code and convert them into
Drawablesobjects.The following example code shows how to create an
Bitmap object for the assets folder and assign it to an ImageView.// Get the AssetManager
AssetManager manager = getAssets();
// read a Bitmap from Assets
InputStream open = null;
try {
open = manager.open("logo.png");
Bitmap bitmap = BitmapFactory.decodeStream(open);
// Assign the bitmap to an ImageView in this layout
ImageView view = (ImageView) findViewById(R.id.imageView1);
view.setImageBitmap(bitmap);
} catch (IOException e) {
e.printStackTrace();
} finally {
if (open != null) {
try {
open.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
You can also access the Drawables from your
res/drawable folder as Bitmap objects in your source code. The following code demonstrates that.Bitmap b = BitmapFactory.decodeResource(getResources(), R.drawable.ic_action_search);
You can create a scale bitmap based on a new weight and height definition in pixel.
Bitmap originalBitmap = <initial setup>;
Bitmap resizedBitmap =
Bitmap.createScaledBitmap(originalBitmap, newWidth, newHeight, false);
To convert a
Bitmap object into a Drawable you can use the following code.# Convert Bitmap to Drawable
Drawable d = new BitmapDrawable(getResources(),bitmap);
Shape Drawables are XML files which allow to define a geometric object with colors, borders and gradients which can get assigned to
Views. The advantage of using XML Shape Drawables is that they automatically adjust to the correct size.The following listing shows an example of a Shape Drawable.
<?xml version="1.0" encoding="UTF-8"?>
<shape
xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="rectangle">
<stroke
android:width="2dp"
android:color="#FFFFFFFF" />
<gradient
android:endColor="#DDBBBBBB"
android:startColor="#DD777777"
android:angle="90" />
<corners
android:bottomRightRadius="7dp"
android:bottomLeftRadius="7dp"
android:topLeftRadius="7dp"
android:topRightRadius="7dp" />
</shape>
You could for example assign that drawable to the background property of your layout.
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@drawable/myshape"
android:orientation="vertical" >
<EditText
android:id="@+id/editText1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
>
</EditText>
<RadioGroup
android:id="@+id/radioGroup1"
android:layout_width="match_parent"
android:layout_height="wrap_content" >
<RadioButton
android:id="@+id/radio0"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:checked="true"
android:text="@string/celsius" >
</RadioButton>
<RadioButton
android:id="@+id/radio1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/fahrenheit" >
</RadioButton>
</RadioGroup>
<Button
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/calc"
android:onClick="myClickHandler">
</Button>
</LinearLayout>
State drawables allow to define states. For each state a different drawable can get assigned to the
View. For example the following defines different drawables for a button depending on its state.<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<item android:drawable="@drawable/button_pressed"
android:state_pressed="true" />
<item android:drawable="@drawable/button_checked"
android:state_checked="true" />
<item android:drawable="@drawable/button_default" />
</selector>
Transition Drawables allow to define transitions which can be triggered in the coding.
<?xml version="1.0" encoding="utf-8"?>
<transition xmlns:android="http://schemas.android.com/apk/res/android">
<item android:drawable="@drawable/first_image" />
<item android:drawable="@drawable/second_image" />
</transition>
final ImageView image = (ImageView) findViewById(R.id.image);
final ToggleButton button = (ToggleButton) findViewById(R.id.button);
button.setOnClickListener(new OnClickListener() {
@Override
public void onClick(final View v) {
TransitionDrawable drawable = (TransitionDrawable) image.getDrawable();
if (button.isChecked()) {
drawable.startTransition(500);
} else {
drawable.reverseTransition(500);
}
}
});
You can also define an animation drawables and assign it to a
View via thesetBackgroundResource() method.<!-- Animation frames are phase*.png files inside the
res/drawable/ folder -->
<animation-list android:id="@+id/selected" android:oneshot="false">
<item android:drawable="@drawable/phase1" android:duration="400" />
<item android:drawable="@drawable/phase2" android:duration="400" />
<item android:drawable="@drawable/phase3" android:duration="400" />
</animation-list>
ImageView img = (ImageView)findViewById(R.id.yourid);
img.setBackgroundResource(R.drawable.your_animation_file);
// Get the AnimationDrawable object.
AnimationDrawable frameAnimation = (AnimationDrawable) img.getBackground();
// Start the animation (looped playback by default).
frameAnimation.start();
Alternative you can implement a class which extends
Drawable and implements Animatable.9 Patch drawables are Drawables which have a one pixel additional border. On the top and left you define the area which should be scaled if the Drawable is to small for the view. This is the stretch area.
On the right and bottom side you define the area where a text should be placed if this
Drawable is used on a view which can write text on it, e.g. a Button.The ADT supplies the
draw9patch program in the android-sdk/tools installation folder, which makes it easy to create 9 Patch drawables.A nice online generator for 9 patch drawables can be found under the following URL: Simple Nine-patch generator .
You can also create custom Drawable, which can use the Canvas API for their display. For these drawables you can use the full Canvas API to design them to your need.
Create the following Android project called com.vogella.android.drawables.custom based on theBlankActivity template.
Create the following custom Drawable class.
package com.vogella.android.drawables.custom;
import android.graphics.Bitmap;
import android.graphics.BitmapShader;
import android.graphics.Canvas;
import android.graphics.ColorFilter;
import android.graphics.Paint;
import android.graphics.RectF;
import android.graphics.Shader;
import android.graphics.drawable.Drawable;
public class MyRoundCornerDrawable extends Drawable {
private Paint paint;
public MyRoundCornerDrawable(Bitmap bitmap) {
BitmapShader shader;
shader = new BitmapShader(bitmap, Shader.TileMode.CLAMP,
Shader.TileMode.CLAMP);
paint = new Paint();
paint.setAntiAlias(true);
paint.setShader(shader);
}
@Override
public void draw(Canvas canvas) {
int height = getBounds().height();
int width = getBounds().width();
RectF rect = new RectF(0.0f, 0.0f, width, height);
canvas.drawRoundRect(rect, 30, 30, paint);
}
@Override
public void setAlpha(int alpha) {
}
@Override
public void setColorFilter(ColorFilter cf) {
}
@Override
public int getOpacity() {
return 255;
}
}
To use it change your layout file to the following.
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity" >
<ImageView
android:id="@+id/image"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:contentDescription="TODO" />
</RelativeLayout>
Change your
MainActivity class to the following. The code assumes that you have a bitmap in yourdrawable folder called dog.png.package com.vogella.android.drawables.custom;
import java.io.InputStream;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.view.Menu;
import android.widget.ImageView;
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ImageView button = (ImageView) findViewById(R.id.image);
InputStream resource = getResources().openRawResource(R.drawable.dog);
Bitmap bitmap = BitmapFactory.decodeStream(resource);
button.setBackground(new MyRoundCornerDrawable(bitmap));
}
}
No comments:
Post a Comment