Toast的使用

Toast的基本原理其实就是将一个View添加到WindowManager中，让WindowManager来把View显示出来。（WindowManager可以将View显示在任何地方，任何Activity之上）


Toast的默认属性

// 对其方式为：水平居中，并在底部
mGravity = Gravtiy.CENTER_HORIZONTAL | Gravtiy.BOTTOM;

mX = 0;
mY =context.getResources().getDimensionPixelSize(com.android.internal.R.dimen.toast_y_offset);

mHorizontalMargin = 0;
mVerticalMargin = 0;

所以用Toast.makeText(getApplicationContext(), R.string.text, Toast.LENGTH_SHORT).show();生成的Toast总是处在底部水平居中的位置

在指定x, y处显示Toast

// 在(50, 100)处显示Toast
Toast toast = Toast.makeText(getApplicationContext(), "toast use", Toast.LENGTH_SHORT);
toast.setGravity(Gravity.TOP | Gravity.LEFT, 50, 100);
toast.show();

// 如果使用Gravity.NO_GRAVITY，后面的x, y就是相对于屏幕的中心点的（估计android是默认这么处理的）
Toast toast = Toast.makeText(getApplicationContext(), "toast use", Toast.LENGTH_SHORT);
toast.setGravity(Gravity.NO_GRAVITY, 50, 100);
toast.show();

// 用margin来控制toast的位置
Toast toast = Toast.makeText(getApplicationContext(), "toast use", Toast.LENGTH_SHORT);
toast.setGravity(Gravity.LEFT | Gravity.TOP, 0, 0);
// leftMargin, topMargin分别是容器width, height的%多少(这里是10%和20%)
toast.setMargin(0.1F, 0.2F);
toast.show();

指定View的Toast

// 布局xml：R.layout.toast
< Button
	xmlns:android="http://schemas.android.com/apk/res/android"
	android:id="@android:id/message"
	android:layout_width="fill_parent"
	android:layout_height="wrap_content" />


Toast toast = new Toast(getApplicationContext());
toast.setView(LayoutInflater.from(getApplicationContext()).inflate(R.layout.toast, null));
toast.setText("toast use");
// Button是否fill_parent是由gravity控制的, xml中的不起任何作用
toast.setGravity(toast.getGravity() | Gravity.FILL_HORIZONTAL, 
	toast.getXOffset(), toast.getYOffset());
toast.setDuration(Toast.LENGTH_SHORT);
toast.show();

Toast部分源码

// Toast的构造器只设置了mY这个属性。mNextView, mDuration都没有设置(用makeText的话，这两个属性会设置)
public Toast(Context context) {
	mContext = context;
	mTN = new TN();
	mY = context.getResources().getDimensionPixelSize(com.android.internal.R.dimen.toast_y_offset);
}

// setText方法，需要将显示text的view的id设为@android:id/message，否则会抛RuntimeException
public void setText(CharSequence s) {
	if (mNextView == null) {
		throw new RuntimeException("This Toast was not created with Toast.makeText()");
	}
	TextView tv = (TextView) mNextView.findViewById(com.android.internal.R.id.message);
	if (tv == null) {
		throw new RuntimeException("This Toast was not created with Toast.makeText()");
	}
	tv.setText(s);
}

一直显示的Toast
实现原理是：在Toast隐藏之前，再show一个相同的Toast，来实现长显示的假象

private class ToastWrapper {
	private Toast mToast;
	
	private Handler mHandler;
	
	private Runnable mShowToast = new Runnable() {
		@Override
		public void run() {
			continueShow();
		}
	};
	
	private boolean mCancelled = true;
	
	public ToastWrapper(Context ctxt) {
		this(ctxt, new Handler());
	}
	
	public ToastWrapper(Context ctxt, Handler handler) {
		mToast = Toast.makeText(ctxt, null, Toast.LENGTH_SHORT);
		mHandler = handler;
	}
	
	public Toast getToast() {
		return mToast;
	}
	
	public void showUntilCancel() {
		if (mCancelled) {
			mCancelled = false;
			mToast.setDuration(Toast.LENGTH_LONG);
			continueShow();
		}
	}
	
	public void cancel() {
		mCancelled = true;
		mToast.cancel();
	}
	
	private void continueShow() {
		if (mCancelled) {
			return;
		}
		mToast.show();
		mHandler.postDelayed(mShowToast, 3000);
	}
}

使用ToastWrapper

// 一直显示的toast
toastWrapper = new ToastWrapper(getApplicationContext());
Toast toast = toastWrapper.getToast();
toast.setText("toast wrapper");

// ...

Button button = new Button(getApplicationContext());
button.setText("一直显示toast");
button.setOnClickListener(new View.OnClickListener() {
	@Override
	public void onClick(View view) {
		toastWrapper.showUntilCancel();
	}
});

Button button = new Button(getApplicationContext());
button.setText("隐藏toast");
button.setOnClickListener(new View.OnClickListener() {
	@Override
	public void onClick(View view) {
		toastWrapper.cancel();
	}
});



// 一搬的toast
Button button = new Button(getApplicationContext());
button.setText("一般的toast");
button.setOnClickListener(new View.OnClickListener() {
	@Override
	public void onClick(View view) {
		Toast toast = toastWrapper.getToast();
		toast.setDuration(Toast.LENGTH_SHORT);
		toast.show();
	}
});